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Effects of Prebreeding Body Weight or Progestin Exposure Before Breeding on Beef Heifer Performance Through the Second Breeding Season
Abstract
Two experiments evaluated prebreeding target BW or progestin exposure for heifers developed lighter than traditional recommendations. Experiment 1 evaluated the effects of the system on heifer performance through subsequent calving and rebreeding over 3 yr. Heifers (229 kg) were assigned randomly to be developed to 55% of mature BW (299 kg) before a 45-d breeding season (intensive, INT; n = 119) or 50% of mature BW (272 kg) before a 60-d breeding season (relaxed, RLX; n = 142). Prebreeding and pregnancy diagnosis BW were greater (P <or= 0.006) for INT than RLX heifers. Overall pregnancy rate did not differ (88.4%; P = 0.51), but RLX heifers had later calving dates (7 d; P < 0.001) and lighter calf weaning weights (194 +/- 4 vs. 199 +/- 4 kg; P < 0.07) compared with INT heifers. Calf birth weight, calving difficulty, second-calf conception rates, and 2-yr-old retention rate did not differ (P > 0.15) between systems. Cost per pregnant 2-yr-old cow was less for the RLX than the INT heifer development system. Of heifers that failed to become pregnant, a greater proportion (P = 0.07) of heifers in the RLX than in the INT system were prepubertal when the breeding season began. Therefore, a second 2-yr experiment evaluated melengestrol acetate (MGA, 0.5 mg/d) as a means of hastening puberty in heifers developed to 50% of mature BW. Heifers were assigned randomly to the control (n = 103) or MGA (n = 81) treatment for 14 d and were placed with bulls 13 d later for 45 d. Prebreeding and pregnancy diagnosis BW were similar (280 and 380 kg, respectively; P > 0.10) for heifers in the control and MGA treatments. The proportion of heifers pubertal before breeding (74%), pregnancy rate (90%), calving date, calf weaning weight, and second breeding season pregnancy rate (92%) were similar (P > 0.10) between treatments. Developing heifers to 50 or 55% of mature BW resulted in similar overall pregnancy rates, and supplementing the diets of heifers developed to 50% of mature BW with MGA before breeding did not improve reproductive performance.
... Once replacement heifers have been weaned and selected, management strategies are implemented to ensure their proper growth and development prior to breeding. Nutritional management should ensure that replacements reach a target weight of 55 to 65% of expected mature weight prior to the start of their first breeding season [9,10]. Previous studies have shown RTS, BCS, and frame score are useful in selecting for quality replacement heifers in large beef herds in the United States [9][10][11][12]. ...
... Nutritional management should ensure that replacements reach a target weight of 55 to 65% of expected mature weight prior to the start of their first breeding season [9,10]. Previous studies have shown RTS, BCS, and frame score are useful in selecting for quality replacement heifers in large beef herds in the United States [9][10][11][12]. ...
... There was no association between RTS and any of the pregnancy outcomes analyzed compared to previous research published [29,30]. A previous study noted RTS was significantly associated with pregnancy outcomes by itself, but was found insignificant when adding additional variables to the model [10]. In this group of heifers, the median days to pregnancy varied by only one day between all RTS. ...
Developing and raising replacement heifers requires a large capital investment for producers. Therefore, it is imperative to discover traits and management practices to eliminate subfertile heifers prior to breeding and pregnancy determination. In this study, four years of data was analyzed from a centralized beef heifer development yard in the Midwest of the United States. The objective of this study was to analyze various heifer physical characteristics and management practices in order to quantify their impact on pregnancy and date of conception. Logistic regression models were built to investigate risk factors associated with conception to artificial insemination (AI), pregnancy by natural service after AI exposure, and pregnancy in the first 21-days of the breeding season. Age at entry, average daily gain from entry to breeding, pelvic width, and year were associated with AI pregnancy (p < 0.05). On the second model, average daily gain from entry to yearling weight, weight at breeding, weight at pregnancy diagnosis, and age at AI were significantly associated with pregnancy. There were no associations with reproductive tract score with any of the response variables analyzed. These results indicate there are physical measurements that can be used to improve the ability to select and develop heifers for improved reproductive performance.
... Heifer reproductive success in the first calving season is highly linked with lifetime reproductive efficiency [9][10][11]. A compilation of data from multiple studies demonstrated that first breeding season pregnancy rates in beef heifers range from 64 to 95% under natural breeding (NB) alone or the combination of artificial insemination (AI) followed by NB ( [12][13][14][15][16][17][18][19][20][21][22][23] (Fig. 1)). Altogether, an average of 85% of heifers become pregnant by the completion of the breeding season. ...
... Pregnancy rate to artificial insemination tended to be reduced in heifers developed to 55% [13], but was not reduced in heifers developed to 56% of mature body weight [17]. The development of heifers to 50% versus 55% of mature bodyweight also yielded no difference in overall 45-d breeding season pregnancy rates, but significantly delayed the date of first calving [19]. ...
... Such protocols synchronize ovulation in heifers and allow all heifers to be inseminated on day one of the breeding season. Overall, progestin based synchronization programs have a positive influence on heifer calving date and breeding season pregnancy rates [18,19,32,59]. ...
The development of replacement heifers is at the core of cow-calf beef production systems. In 2020, the USDA, National Agricultural Statistics Service reported 5.771 million beef heifers, 500 pounds and over, are under development for cow replacement. A compilation of data from several studies indicate that between 85% and 95% of these heifers will become pregnant in their first breeding season. Several thousands of heifers being raised for replacement may not deliver a calf on their first breeding season and result in economic losses to cow-calf producers. Many management procedures have been developed to maximize the reproductive potential of beef heifers. Such approaches include, but are not limited to the following: nutritional management for controlled weight gain, identification of reproductive maturity by physiological and morphological indicators, and the implementation of an estrous synchronization program. The implementation of management strategies has important positive impact(s) on the reproductive efficiency of heifers. There are limitations, however, because some heifers deemed ready to enter their first breeding season do not become pregnant. In parallel, genetic selection for fertility-related traits in beef heifers have not promoted major genetic gains on this particular area, most likely due to low heritability of female fertility traits in cattle. Technologies such as antral follicle counting, DNA genotyping and RNA profiling are being investigated as a means to aid in the identification of heifers of low fertility potential. To date, many polymorphisms have been associated with heifer fertility, but no DNA markers have been identified across herds. Antral follicle count is an indication of the ovarian reserve and is an indicator of the reproductive health of a heifer. We have been working on the identification of transcriptome profiles in heifers associated with pregnancy outcome. Our current investigations integrating protein-coding transcript abundance and artificial intelligence have identified the potential for bloodborne transcript abundance to be used as indicators of fertility potential in beef heifers. In summary, there is an ongoing pressure for reducing costs and increasing efficiency in cow-calf production systems, and new technologies can help reduce the long-standing limitations in beef heifer fertility.
... Age at puberty depends on the diets applied from 4 to 6 mo [2] and after weaning [3]. To achieve this target, postweaning growth should guarantee that heifers reach 65% of mature BW at breeding [4], although other studies proposed to reduce this threshold to 50%-55% [5,6]. Moreover, the heifers should reach 80% of mature BW [7] at first calving, with adequate skeletal development. ...
... Two heifers failed to get pregnant and were removed from the experiment at the end of the breeding season, which resulted in the following composition of the experimental groups thereafter: PA-HIGH (6 heifers), PA-MOD (6), PI-HIGH (6), and PI-MOD (5). ...
... The similar weight gains observed in heifers of both breeds throughout the study agree with previous results described in works both with heifers and growing bulls [20], likely due to their similar intake capacity [26] and feed conversion efficiency [28]. Considering their similar mature BW (580 kg [17]), at the time of conception, all heifers exceeded the minimum recommended BW to avoid future detriment to dam performance, that is, either 65% of mature BW [4] or the more restrictive 50%-55% recommendation [5,6]. After gestation on a common diet, heifer BW and BCS at calving were similar in all treatments and in accordance with those described in PA heifers having their first calving at 2 yr [8], but lighter than those of 2.5 yr-old PA primiparous [17]. ...
The aim of this study was to examine the effects of 2 postweaning feeding management approaches (FEED: 0.8 [HIGH] vs 0.6 [MOD] kg/d target ADG) on the performance of heifers of 2 beef breeds (BREED: Parda de Montaña [PA] vs Pirenaica) calving at 2 yr. Twenty-five heifers previously creep fed before weaning (6 mo) were assigned to 2 planes of nutrition from 6 to 15 mo of age. At 15 mo, they were inseminated, and then received similar diets until weaning of their first calf (4 mo postcalving). Several parameters were measured to analyze growth and development (BW; ADG; size measures at 6 mo, 15 mo, calving, and weaning), performance at puberty and first breeding, and dam and calf performance in the first lactation (calving traits, ADG, milk yield). Metabolic (glucose, cholesterol, NEFA, β-hydroxybutyrate, and urea) and endocrine status (IGF-I and leptin) were assessed in plasma samples collected every 3 mo from 6 mo to calving and monthly during lactation. No interaction between BREED and FEED was observed. Heifers from the HIGH feeding treatment had higher postweaning ADG than those on the LOW diet. At 15 mo, they had greater BW, heart girth, and external pelvic area, but they did not differ thereafter. All heifers reached puberty at similar BW (55% mature BW) but different ages. Heifers from the HIGH treatment tended (P < 0.09) to be pubertal earlier, and PA heifers were 1.6 mo younger than Pirenaica heifers (P < 0.05) at puberty. At the time of conception (452 ± 59 kg) and calving (471 ± 51 kg), BW was above common recommendations in all groups. Calving traits and performance in lactation did not differ between feeding treatments. BREED only influenced birth weight; PA calves being heavier (P < 0.05), which resulted in a larger calf/cow BW ratio, but no effect on calving difficulty or subsequent performance. Metabolic substrates and hormones depended mostly on sampling date, which was related to current energy and protein intake. Glucose (P < 0.001), cholesterol (P < 0.001), and IGF-I (P < 0.05) were greater during the postweaning phase in heifers on the HIGH diet, and persistent physiological effects were observed during lactation. Age at puberty was negatively related with IGF-I (r = -0.43, P < 0.001), but not with leptin concentrations. In conclusion, regardless of breed, a moderate growth rate ensured adequate heifer development and performance until the first lactation, whereas no advantage was gained from enhanced postweaning gains.
... Female infertility remains a limiting factor in cattle production systems. In beef heifers, pregnancy rates vary from 53% to 95% [1][2][3][4][5][6][7][8][9][10] under natural breeding (NB), and are reduced to the range of 48-69% [1,4,7,9,11,12] if artificial insemination (AI) is the only breeding strategy utilized. Best management practices in heifer development have been used to increase the probability of reproductive success in a heifer's first breeding season [13]. ...
... Best management practices in heifer development have been used to increase the probability of reproductive success in a heifer's first breeding season [13]. For instance, heifers that reach 60% of their mature body weight [10], have a body conformation compatible with a healthy and well-nourished animal [3,14], present reproductive structures indicative of cyclic animals [9,15,16], and are bred on their third estrus versus earlier cycles [8] may have a greater chance of becoming pregnant early in the breeding season [13]. Yet, under appropriate management, many of the heifers that are deemed reproductively mature according to morphological assessment and age criteria do not become pregnant. ...
... Thus, we interrogated the entire dataset (23 samples) under the binary classification of AI-pregnant (N = 12) and AI-not-pregnant (N = 11). There were four genes forming two pairs (C11orf54, TAF1B; URB2, ENSTAG00000039129) that discriminated 10 The clustering of 10 out of 12 AI-pregnant heifers independently from NB-pregnant and non-pregnant heifers, showed non-trivial (P < 0.003, hypergeometric test) patterns of ratios that identified heifers by pregnancy outcome, and clearly contrasted with ratio patterns obtained from random gene pairs (Fig. 3f ). ...
Background:
Infertility is a longstanding limitation in livestock production with important economic impact for the cattle industry. Female reproductive traits are polygenic and lowly heritable in nature, thus selection for fertility is challenging. Beef cattle operations leverage estrous synchronization in combination with artificial insemination (AI) to breed heifers and benefit from an early and uniform calving season. A couple of weeks following AI, heifers are exposed to bulls for an opportunity to become pregnant by natural breeding (NB), but they may also not become pregnant during this time period. Focusing on beef heifers, in their first breeding season, we hypothesized that: a- at the time of AI, the transcriptome of peripheral white blood cells (PWBC) differs between heifers that become pregnant to AI and heifers that become pregnant late in the breeding season by NB or do not become pregnant during the breeding season; and b- the ratio of transcript abundance between genes in PWBC classifies heifers according to pregnancy by AI, NB, or failure to become pregnant.
Results:
We generated RNA-sequencing data from 23 heifers from two locations (A: six AI-pregnant and five NB-pregnant; and B: six AI-pregnant and six non-pregnant). After filtering out lowly expressed genes, we quantified transcript abundance for 12,538 genes. The comparison of gene expression levels between AI-pregnant and NB-pregnant heifers yielded 18 differentially expressed genes (DEGs) (ADAM20, ALDH5A1, ANG, BOLA-DQB, DMBT1, FCER1A, GSTM3, KIR3DL1, LOC107131247, LOC618633, LYZ, MNS1, P2RY12, PPP1R1B, SIGLEC14, TPPP, TTLL1, UGT8, eFDR≤0.02). The comparison of gene expression levels between AI-pregnant and non-pregnant heifers yielded six DEGs (ALAS2, CNKSR3, LOC522763, SAXO2, TAC3, TFF2, eFDR≤0.05). We calculated the ratio of expression levels between all gene pairs and assessed their potential to classify samples according to experimental groups. Considering all samples, relative expression from two gene pairs correctly classified 10 out of 12 AI-pregnant heifers (P = 0.0028) separately from the other 11 heifers (NB-pregnant, or non-pregnant).
Conclusion:
The transcriptome profile in PWBC, at the time of AI, is associated with the fertility potential of beef heifers. Transcript levels of specific genes may be further explored as potential classifiers, and thus selection tools, of heifer fertility.
... This work is a genuine collaborative effort, where the animal scientists and economist have worked closely in the construction and development of the complete project. The animal data for this project are from research conducted by reproductive physiologists at University of Nebraska-Lincoln's West Central Research and Extension Center Deutscher 2004 andMartin et al. 2008). The application of economic and the construction of the physical portions of that model were done by the economist with input from the biological scientist. ...
... For this reason, scientists and producers generally use an average mature weight to approximate the pre-breeding weight percentage. The percent of herd average weight (PHAW) was used as a proxy by Funston and Deutscher (2004) and Martin et al. (2008) in the original heifer development study. ...
... While this methodology enables scientists to control the experiment and test for effects of single variables, it eliminates the effects of some factors that might have significant bearing on the question being asked. In the experiments by Funston and Deutscher (2004) and Martin et al. (2008), differences in heifer size because of feeding programs were analyzed, but differences in size because of genetic potential or other factors were eliminated in the randomization process. The effect that genetic potential has on heifer size at the first breeding period, or how this potential responds to nutritional requirements for reproductive success, were not included in their experimental design. ...
Maturity Index (MI) was used in a Probit regression as an explanatory variable of dystocia, where dystocia was used in a Probit regression as an explanatory variable of rebreeding rates of primiparous cows from data collected on replacement heifers from the Gudmundsen Sandhills Laboratory. Dystocia was found to decrease from about 40% to 13% for heifers when the MI increased from 53 to 70, supporting the notion that maturity reduces the incidence of dystocia, resulting in an increase in the second pregnancy rate.
... This work is a genuine collaborative effort, where the animal scientists and economist have worked closely in the construction and development of the complete project. The animal data for this project are from research conducted by reproductive physiologists at University of Nebraska-Lincoln's West Central Research and Extension Center Deutscher 2004 andMartin et al. 2008). The application of economic and the construction of the physical portions of that model were done by the economist with input from the biological scientist. ...
... For this reason, scientists and producers generally use an average mature weight to approximate the pre-breeding weight percentage. The percent of herd average weight (PHAW) was used as a proxy by Funston and Deutscher (2004) and Martin et al. (2008) in the original heifer development study. ...
... While this methodology enables scientists to control the experiment and test for effects of single variables, it eliminates the effects of some factors that might have significant bearing on the question being asked. In the experiments by Funston and Deutscher (2004) and Martin et al. (2008), differences in heifer size because of feeding programs were analyzed, but differences in size because of genetic potential or other factors were eliminated in the randomization process. The effect that genetic potential has on heifer size at the first breeding period, or how this potential responds to nutritional requirements for reproductive success, were not included in their experimental design. ...
The determination of the ideal breeding size of beef replacement females is traditionally centered on maximizing pregnancy rate. Relevant physical and economic relationships were combined into a bioeconomic systems model that identified key profit factors. This system-wide approach encapsulated the physical relationships with relevant costs and revenues, including annual and seasonal variations and measures relative to profitability through the application of an incomplete or modified profit function. Optimaloutcomes were relative to heifer size and management regime.
... This work is a genuine collaborative effort, where the animal scientists and economist have worked closely in the construction and development of the complete project. The animal data for this project are from research conducted by reproductive physiologists at University of Nebraska-Lincoln's West Central Research and Extension Center Deutscher 2004 andMartin et al. 2008). The application of economic and the construction of the physical portions of that model were done by the economist with input from the biological scientist. ...
... For this reason, scientists and producers generally use an average mature weight to approximate the pre-breeding weight percentage. The percent of herd average weight (PHAW) was used as a proxy by Funston and Deutscher (2004) and Martin et al. (2008) in the original heifer development study. ...
... While this methodology enables scientists to control the experiment and test for effects of single variables, it eliminates the effects of some factors that might have significant bearing on the question being asked. In the experiments by Funston and Deutscher (2004) and Martin et al. (2008), differences in heifer size because of feeding programs were analyzed, but differences in size because of genetic potential or other factors were eliminated in the randomization process. The effect that genetic potential has on heifer size at the first breeding period, or how this potential responds to nutritional requirements for reproductive success, were not included in their experimental design. ...
Recent research on the economics of optimal beef replacement heifer size development reinforced the established economic principle that revenue or cost optimization are not equal to profit optimization. A modified profit function was used to analyze simulated results which demonstrated the differences among the three measures. In the case of optimizing pregnancy rates, a heifer must be heavier to optimize productivity as measured by revenue verses profit. Similarly in the case of cost minimization, the reduction in developmental expenses results in less profit except in the case where the economically optimal sized heifer equals that of the size chosen to cost minimize.
... There is increasing interest in lower cost, low-gain heifer development systems. Recent data (Funston and Deutscher, 2004;Martin et al., 2008) indicate beef heifers reaching less than recommended guidelines of 60 to 66% of mature BW (Patterson et al., 1992) do not have decreased overall pregnancy rates in a 45-d breeding season. ...
... However, Martin et al. (2008) did observe a later calving date for heifers developed to 51 versus 57% of mature BW, indicating a delayed breeding date. Supplementation offered to nutritionally restricted multiparous females before breeding improves embryo survival (Khireddine et al., 1998), but how this type of supplementation may interact with low-gain heifer development is unknown. ...
... Previous data suggest heifers should reach 65% of mature BW by the first insemination for a successful breeding season (Patterson et al., 1992). More recent research indicates heifers reaching less than 60% of their mature BW before breeding have similar pregnancy rates in a 45-d breeding season (Funston and Deutscher, 2004;Martin et al., 2008). Further, final heifer pregnancy rate does appear to be greatly dependent on age at puberty, which is inversely correlated with postweaning growth rate (Lynch et al., 1997;Freetly et al., 2001). ...
Experiments evaluated estrus synchronization and periconceptual supplementation on pregnancy rate and calf production. Approximately one-half of heifers in 2 pastures (yr 1) or 4 pastures (yr 2) were injected with prostaglandin F2α (PGF; n = 1,182) or not (NPGF; n = 1,208) 5 d after fertile bulls were introduced for 25 d. In yr 2, a total of 1,230 heifers were randomly assigned to 1 of 4 pastures; 2 received a supplement providing 100 g/d of Ca propionate (1.4 kg/d, 20% CP) 2 d before through 19 d after bull exposure and 2 did not in a 25-d breeding season.
Pregnancy rate was reduced (P < 0.01) in the PGF-synchronized heifers relative to the NPGF heifers (73.7 vs. 78.3% for PGF and NPGF, respectively. Approximately 10% more (P < 0.01) PGF-synchronized heifers that became pregnant calved in the first 21 d. Subsequently, weaning weight and the value of steer calves from PGF dams tended to be greater (P < 0.10) than those of steer calves from NPGF dams. Supplemented heifers were heavier (P < 0.05) at pregnancy diagnosis; however, pregnancy rate was unaffected (P > 0.10). Calf birth weight was greater (P < 0.05) for calves from dams receiving the Ca propionate supplement, but weaning weight and calf value were similar (P > 0.10). In this study, injection of PGF in a 25-d breeding season improved synchrony of calving and increased steer calf weaning weight and value; however, supplemental nutrition during the periconceptual period was of limited value.
... A study of low input heifer systems by Martin et al. (2008) found that, despite above-target weights at breeding, heifers that were reared through either a relaxed or intensive rearing system, both weighed less than 90% of predicted mature weight at calving. ...
... There was no significant difference in predicted calving success when heifers were below, on or above target weight at any age in the current study. This is supported by two studies which state that developing a heifer to 53% of her mature body weight at service had no adverse effect on calf production (Funston and Deutscher, 2004;Martin et al., 2008). It was noted that, for each age band, the numbers recorded as below target were lower than those either on target or above target. ...
... They also found that heifers with a higher growth rate had larger pelvic areas at 24 months and should have less calving difficulty. Martin et al. (2008) found no significant difference between the amount of assistance required for heifers reared to 50.9% of mature body weight at mating, compared with that required for those reared to 56.5% of mature body weight at mating. In the current study, heifers that were on-target at 20-21 months were significantly (P < 0.05) more likely to have calving difficulties than those that were underweight. ...
A decision-support tool that automatically selects an age-specific target weight for beef heifers and specifies the daily liveweight gain (DLWG) required to achieve this target weight within 3 months was developed as an aid for farmers to use to promote calving at 24 months of age in the Northern Ireland suckler herd. The ability of Northern Ireland beef producers to follow this target-driven growth management plan and calve heifers at 24 months of age was appraised in a study involving a total of 459 heifers of 10 breeds on six suckler farms. A unique growth curve was generated for each farm, with the aim of achieving 60% and 90% of the estimated mature weight of their cows at 14 months and 24 months respectively. Mature weight was estimated using the 6.7% truncated mean weight of mature cows on each farm. At intervals of 3 months, heifer weight, body condition score (BCS) and diet quality and quantity were assessed on each farm and a target weight for the next visit was specified, along with the DLWG required to achieve that target weight. Typically, heifers were significantly above their target weight prior to 9 months of age (P < 0.05), but farmers were able to manage heifers so as to keep them within ±5% of their individual growth targets after the age of 9 months. Heifer breed and season of birth did not influence adherence to target weight, while individual animal and farm of origin accounted for 51.3% and 24.7%, respectively, of the variation. Adherence to the target growth curve was not influenced by whether or not a heifer produced a live calf, nor by that calf's vitality, but it was associated with the heifer's calving temperament, calving difficulty and mothering ability. Heifers that met target weight between 22 and 24 months of age had significantly heavier calves than those that were below their target weight at this age (P < 0.05). The mean age at first calving was reduced by an average of 3.74 months across the six farms (P < 0.001) as a result of applying the growth management plan. Experiences of the producers have helped to shape the development of an on-line decision support tool and to promote its use. It is anticipated that this support tool will assist producers adopt target-driven growth monitoring for replacement beef heifers, resulting in a higher prevalence of optimal 24-month first calving in Northern Ireland.
... Traditionally, the recommendation has been that heifers be developed to reach 60 to 65% of mature BW by the onset of the breeding season (Patterson et al., 1992). However, recent research has demonstrated heifers reaching less than 58% of mature BW by breeding do not display impaired reproductive performance (Funston and Deutscher, 2004;Martin et al., 2008;Funston et al., 2012). In today's beef industry, meeting heifer maintenance and gestation nutrient requirements can increase overall development costs for beef producers. ...
... Earlier studies have indicated heifers should exhibit 2 or 3 estrous cycles before the start of the breeding season; as Byerley et al. (1987) reported, the first estrus pregnancy rate was 21% lower compared with heifers bred on the third estrus. The 63-d breeding season may have allowed more heifers to achieve puberty and become pregnant; however, the percentage of heifers pregnant after 45 d (98 and 95% for MG and HG, respectively; data not shown) of the breeding season in the current study is similar to other studies where heifers were exposed to bulls for a 45-d breeding season (Martin et al., 2008). The BW differences between the winter development systems were maintained over the second winter, breeding, and summer grazing periods; thus, precalving BW was greater (P = 0.02) for HG than for MG heifers (Table 4). ...
... However, when compared over a 202 d development period, developing heifers in the HG system increased total costs $58/head (21% higher), mainly due to an increase in feed and labor costs (Table 6). Developing heifers to attain a target BW of 55% of Roberts et al., 2007, Roberts et al., 2009Martin et al., 2008;Larson et al., 2011) that demonstrated that developing replacement heifers to lighter target BW ranging from 50 to 57% of mature BW before breeding reduced development costs, but had no negative effect on reproductive performance or subsequent calf performance. Funston and Larson (2011) reported that developing heifers on corn residue or winter range reduced development costs by $45/ pregnant heifer. ...
Reproductive performance was evaluated in beef heifers born over a 2-yr period to determine the effects of target breeding weight (TBW) and development system (SYS) on growth and subsequent reproductive efficiency. Spring-born Angus heifers (253 ± 0.7 kg) were randomly allocated over 2 consecutive yr (yr 1, n = 80; yr 2, n = 96) to be developed to either 55% (350 kg) of mature BW (moderate gain, MG) or 62% (395 kg) of mature BW (high gain, HG). Each MG and HG group was further assigned to 1 of 2 replicated systems (1) bale graze bromegrass-alfalfa round bales in field paddocks (BG); or (2) fed bromegrass-alfalfa round bales in drylot pens (DL). Heifers were fed a diet of bromegrass-alfalfa hay (56.9% TDN; 9.8% CP) and barley grain supplement (85.1% TDN; 12.3% CP). After the 202-d development period, heifers were exposed to bulls for a 63 d breeding season. Target BW × SYS interactions were not detected for any measured parameters. During the winter development period, MG heifers had lower (P = 0.01) ADG than HG heifers and MG heifers had lighter (P = 0.01) BW at breeding. Proportion of heifers attaining puberty by 14.5 mo of age was less (P = 0.05) in MG (20 ± 4%) than HG heifers (52 ± 3%). From the end of the 202-d development period to pregnancy diagnosis, ADG was greater (P = 0.04) in MG heifers than HG heifers (0.83 vs. 0.71 kg/d). First calf pregnancy rates were 86 and 88% for MG and HG heifers, respectively (P = 0.41). Second and third calf pregnancy rates of cows developed in either a MG or HG system as heifers, were not different (P = 0.74) (94.7 vs. 95.9%; 93.8 vs. 93.9%, respectively). Economic analysis revealed a $58 reduced development cost for heifers developed to 55% compared with 62% of mature BW without a loss in reproductive performance.
... Measurements are an average by group rather than an individual measure and used to estimate the mature BW of that group. Patterson et al. (1992) reported 65% mature BW was the recommended target BW at breeding; however, more recent research has demonstrated 55% of mature BW is an adequate target BW for reproductive performance (Funston and Deutscher, 2004;Martin et al., 2008). Greer et al. (1983) theorized the existence of an "index of maturity" and attempted to estimate maturity with age and weaning BW, but concluded neither affected age or BW at first estrus. ...
... Data for this study were collected at the University of Nebraska Gudmundsen Sandhills Laboratory for 2 consecutive research projects (Funston and Deutscher, 2004;Martin et al., 2008), which were continuous and originated from the same cattle herd, making it possible to combine them into a single data set (n = 500). The earlier study included 240 heifers retained as replacements in 1997, 1998, and 1999 whereas 260 heifers in the latter study were retained in 2000, 2001, and 2002. ...
... Similar to Stockton et al. (2012), birth weight was found to be a significant predictor of mature size. Nutrition level was also found to affect maturity, with a 4.8 point difference in MI between the high nutrition level applied by Funston and Deutscher (2004) and the low nutrition level used by Martin et al. (2008), indicating the heifers on the greater planes of nutrition had a greater MI than those on lower planes of nutrition. ...
A target BW is often used to estimate sexual maturity in beef heifers. The target BW, a percentage of mature BW, is generally an average for the breed, herd, or both. Heifer development is done in groups, or herds, and not all heifers respond similarly to the same development regimen. Generally, heifers fed at a higher plain of nutrition gain more and tend to have increased pregnancy rates, but this usually increases feed costs. Thus, determining when increased feed costs exceed the economic gains resulting from higher conception rates is critical and requires the inclusion of economic information and relationships. This research focused on the individual heifer as the decision point, and identification of the individual heifer target BW was based on clearly defined biological relationships observed prior to breeding. These relationships were captured in a maturity index (MI) identified through a series of steps, and guided by current, accepted knowledge of heifer growth and development. Using an in-sample mean absolute percent error comparison, it was determined the MI was more accurate than the current group or herd methods in forecasting actual maturity and target BW. Maturity index demonstrated the flexibility in achieving similar maturities with beef heifers of varying characteristics using alternative nutritional programs. The MI was also the only significant predictor of first pregnancy. These results allow for more precision in determining sexual maturity and probability of first pregnancy in beef heifers, and serve as the basis for future studies in determining profit differences among heifers.
... Feeding replacement heifers to a traditional target weight increases development costs relative to more extensive heifer development (Funston and Deutscher, 2004;Clark et al., 2005;Martin et al., 2007). Funston and Deutscher (2004) reported similar pregnancy rates from the initial through fourth breeding season for heifers developed to reach either 53 or 58% of mature weight prior to breeding as yearlings. ...
... This demonstrated heifers developed to only 53% of mature weight could achieve similar initial pregnancy rates and retention compared to heifers developed to 58% of mature weight. Further research using the same herd found pre-breeding weights as low as 51% of mature weight (RLX) was more cost effective than development to 57% of mature weight (INT) when lighter heifers were allowed 60 d to become pregnant (Martin et al., 2007). Extending the breeding season by 15 d for lighter heifers resulted in first-calf conception rates being similar between systems (45 vs. 60 d breeding season for INT and RLX systems, respectively). ...
... However, feeding heifers to meet traditional recommendations may be unnecessary for successful heifer development. In fact, feeding heifers to traditional target weights increases development costs per pregnant 2-yr-old cow (Clark et al, 2005;Martin et al., 2007). ...
Studies in numerous species provide evidence that diet during development can partially control physiological changes necessary for puberty (Frisch, 1984). Energy balance or plane of nutrition influences reproductive performance in heifers and cows (Short and Adams, 1988; Butler and Smith, 1989; Swanson, 1989; Randel, 1990; Robinson, 1990). Numerous studies have reported inverse correlations between post-weaning growth rate and age at puberty (Wiltbank et al., 1966, 1969, 1985; Short and Bellows, 1971; Arije and Wiltbank, 1971; Ferrell, 1982), and pregnancy rates in heifers were shown to be dependent upon the number displaying estrus prior to or early in the breeding season (Short and Bellows, 1971; Byerley et al., 1987). Thus, rate of postweaning growth was determined to be an important factor affecting age of puberty, which in turn influenced pregnancy rates. This and other research conducted during the late 1960s through the early 1980s indicated puberty occurs at a genetically predetermined size, and only when heifers reach their target weight can high pregnancy rates be obtained (reviewed by Patterson et al., 1992). Guidelines were established stating replacement heifers should be fed to achieve 60 to 65% of their expected mature body weight by the time breeding starts in order to reach puberty. Therefore, traditional approaches for postweaning development of replacement heifers used during the last several decades have primarily focused on feeding heifers to achieve or exceed an appropriate target weight, and thereby maximize heifer pregnancy rates. However, substantial changes in cattle genetics and the economy have occurred over this time, indicating traditional approaches should be re-evaluated. Intensive heifer development systems may maximize pregnancy rates, but not necessarily optimize profit or sustainability. Developing heifers in this manner requires significant use of fossil fuels and cereal grains, and high capital investment in equipment and facilities. The fuel requirement to harvest feed and deliver it to cattle creates high energy demands in this development system. Cereal grains, often used as a major energy source in heifer diets, detract from the system’s sustainability due to growing demand for human food and ethanol production. Since the inception of the target weight guidelines, subsequent research demonstrated the pattern of growth heifers experience prior to achieving a critical target weight could be varied. This provides an opportunity to decrease feed costs by altering rate and timing of gain, creating periods of compensatory growth and/or allowing producers to limit supplementation to critical periods of heifer development (Clanton et al., 1983; Lynch et al., 1997; Freetly et al., 2001). For example, delaying heifer gain until 47 or 56 d prior to the breeding season did not negatively influence reproductive performance, but reduced the amount of feed needed (Lynch et al., 1997). In one year of this study, puberty was delayed in heifers fed to achieve lower early gains, but first-service conception rate tended to be improved in these same heifers. Similarly, Freetly et al. (2001) found delaying gain until the later part of the post-weaning period reduced total energy intake, but calving rate, age at calving, postpartum interval, and second year pregnancy rate were not impacted. This suggests total energy intake, and possibly heifer development costs, may be reduced by limiting heifer gain early in the post-weaning period followed by accelerated gains before the breeding season.
... Recommended guidelines have been to achieve 60 to 65% of mature BW in beef heifers at breeding to optimize reproduction (Patterson et al., 1992). In contrast, Martin et al. (2008) reported that heifers achieving 50% of their mature size before a 45-d breeding season had pregnancy rates of 88.4%. Heifers BW at breeding were 51, 51, and 58% (P < 0.01; Table 5) of mature BW for 36RUP, 50RUP, and DRYLOT heifers, respectively. ...
... In addition, calving date as a 2 yr old was not different (P = 0.89) between heifer development treatments. Previous research developing heifers at similar prebreeding target BW has reported pregnancy rates from 88 to 90% after a 60- (Funston and Deutscher, 2004) or 45-d breeding season (Martin et al., 2008), respectively. In addition, Funston and Larson (2011) reported no difference in fi nal pregnancy rates between heifers developed in a drylot and those grazing corn residue or winter range. ...
... The increase in net return for pasture-developed heifers was due to increased pregnancy rates and decreased development costs. Likewise, restricting BW gain during development by limiting DMI (Roberts et al., 2009a) or developing to a lighter target breeding BW (Martin et al., 2008) also reported economic advantages in low-cost heifer development methods compared with developing heifers at greater rate of BW gain to achieve a certain BW. However, the additional benefi t of increased retention rate was not considered in the enterprise budget, which would have further increased the revenue of developing heifers on pasture. ...
Two studies were conducted to evaluate the effects of post-weaning management of British crossbred heifers on growth and reproduction. In Exp. 1, 239 spring-born, crossbred heifers were stratified by weaning BW (234 ± 1 kg) and allotted randomly to 1 of 2 treatments. Treatments were fed at a rate equivalent to 1.14 kg/d while grazing dormant forage (6.5% CP and 80% NDF; DM basis) and were: (1) 36% CP containing 36% RUP (36RUP), or (2) 36% CP containing 50% RUP (50RUP). Supplementation was initiated in February (1995 and 1996) or November (1997 and 1998) and terminated at the onset of breeding season (mid-May). Heifers were weighed monthly up to breeding and again at time of palpation. After timed AI, heifers were exposed to breeding bulls for 42 ± 8 d. In Exp. 2, 191 spring-born, crossbred heifers were stratified by weaning BW to treatments. Heifer development treatments were: (1) pasture developed and fed 0.9 kg/d of a 36% CP supplement containing 36% RUP (36RUP); (2) pasture developed and fed 0.9 kg/d of a 36% CP supplement containing 50% RUP (50RUP); (3) corn silage based growing diet in a drylot (DRYLOT). Heifers receiving 36RUP and 50RUP treatments were developed on dormant forage. Treatments started in February and ended at the onset of a 45-d breeding season in May. Heifer BW and hip height were taken monthly from initiation of supplementation until breeding and at pregnancy diagnosis. In Exp. 1, BW was not different (P ≥ 0.27) for among treatments at all measurement times. However, 50RUP heifers had greater (P = 0.02; 80 and 67%) pregnancy rates than 36RUP heifers. In Exp. 2, DRYLOT heifers had greater (P < 0.01) BW at breeding than 36RUP or 50RUP developed heifers. However, BW at pregnancy diagnosis was not different (P = 0.24) for between treatments. Pregnancy rates tended to be greater (P = 0.10) for 50RUP heifers than 36RUP and DRYLOT. Net return per heifer was $99.71 and $87.18 greater for 50RUP and 36RUP heifers, respectively compared to DRYLOT heifers due to differences in pregnancy and development costs. Retention rate after breeding yr 3 and 4 was greatest (P ≤ 0.01) for 50RUP heifers. Thus, increasing the supply of metabolizable protein by increasing the proportion of RUP in supplements fed to heifers on dormant forage before breeding increased pregnancy rates, cow herd retention and net return compared to heifers fed in drylot.
... The differences observed in the current study was similar to 8% (fed to appetite, 100% vs. restricted feeding, 80%) [23] and 11% (50 vs. 60% MBW) [8] differences in pubertal status, as a consequence of feeding different quality diets to attain different target BW at breeding. Martin et al. (2008) reported that 17% fewer heifers were pubertal when fed to attain a target bodyweight of 51% MBW compared with 57% MBW at the time of breeding, indicating that greater restriction may have a greater effect on puberty [29]. Most importantly, 11.2% fewer F1 heifers born to dams in the 55% MBW group were pubertal compared to F1 heifers born to dams in the 65% MBW group. ...
... The differences observed in the current study was similar to 8% (fed to appetite, 100% vs. restricted feeding, 80%) [23] and 11% (50 vs. 60% MBW) [8] differences in pubertal status, as a consequence of feeding different quality diets to attain different target BW at breeding. Martin et al. (2008) reported that 17% fewer heifers were pubertal when fed to attain a target bodyweight of 51% MBW compared with 57% MBW at the time of breeding, indicating that greater restriction may have a greater effect on puberty [29]. Most importantly, 11.2% fewer F1 heifers born to dams in the 55% MBW group were pubertal compared to F1 heifers born to dams in the 65% MBW group. ...
Nutrition imprinting carries consequences across generations. The effect of 55% vs. 65% of mature cow body weight (MBW; 545 kg) at breeding on the reproductive performance of heifers and their offspring was investigated. Angus-cross dam heifers were randomly fed to attain 55% (n = 1622) vs. 65% (n = 1578) of MBW, and offspring (F1) heifers born to dam heifers [55% (n = 1285) vs. 65% (n = 1324)] were fed to attain 65% of MBW. Bodyweight and reproductive indices were recorded throughout the study. In dam heifers, puberty (44% vs. 53%), breeding season pregnancy (86.4% vs. 90.6%) and 21-day calving rates (55.2% vs. 65.4%) did vary, but dystocia rate (8.7% vs. 9.0%) did not differ between 55% and 65% MBW groups. Puberty (49.2% vs. 58.2%), breeding season pregnancy (87.2% vs. 92.8%) and 21-day calving rates (53.8% vs. 64.1%) did differ (p < 0.05), but dystocia rate (8.4 vs. 9.2%) did not differ between F1 heifer groups. In conclusion, 55% of MBW at breeding negatively affected the reproductive performance of heifers and its offspring heifers. The recommendation is to feed heifers a balanced diet to reach 65% of MBW at breeding with consideration of production traits.
... Similarly, there was no difference in pregnancy rate after 47 days of breeding in heifers that gained 0.79 kg/day bodyweight from 8 to 15 months of age compared with their contemporaries that gained 0.47 kg/day bodyweight (Eborn et al., 2013). Results of previous research also indicated there were similar final pregnancy rates between heifers developed at different growth rates (Funston and Deutscher, 2004;Martin et al., 2008;Roberts et al., 2009). Providing a diet to heifers with greater energy content or improved pasture for 4-to 6-weeks before breeding which had an earlier growth retardation expedited onset of puberty (Funston and Deutscher, 2004;Roberts et al., 2009). ...
... Notwithstanding all of the previous research results that have been evaluated regarding the positive aspects of enhanced postweaning bodyweight gain, results of several studies indicate there is some flexibility in how target bodyweight is attained (Day and Nogueira, 2013;Cardoso et al., 2014) which, in turn, could be exploited to decrease the overall cost of rearing replacement heifers (Funston et al., 2012). In the present study, heifers that had a greater post-weaning ADG were pubertal at an earlier age and consequently a greater percentage of these heifers were pubertal at the beginning of the breeding season and had a greater 6-week AI rate, which is consistent with results in previous reports (Funston and Deutscher, 2004;Martin et al., 2008;Roberts et al., 2009;Funston and Larson, 2011;Lardner et al., 2014). ...
The aim of this study was to examine the effect of plane of nutrition between 8 and 13 months of age on reproductive performance of heifers of early (EM; n = 154) or late (LM; n = 155) maturing beef breeds and with dairy (dairy-bred, n = 154) or beef (beef-bred, n = 155) dams. Heifers were fed to have an average daily gain (ADG) of 0.50 kg (MOD) or >1.00 kg (HI) for a 141- and 150-day indoor winter period. Subsequently, heifers grazed pasture, and a 12 week breeding programme was implemented. Compared to heifers fed the MOD intake diet, heifers fed the HI intake diet were younger (P < 0.001) and had greater bodyweights (P < 0.001) at puberty but did not have a greater 6- (P = 0.41) or 12- (P = 0.32) week pregnancy rate. Dairy-bred heifers were of a similar age (P = 0.55) but had a lesser bodyweight (P < 0.001) at puberty and had a greater 6- (P < 0.05) and 12- (P < 0.01) week pregnancy rate compared to beef-bred heifers. Compared to LM heifers, EM heifers were younger (P < 0.001), had a lesser bodyweight (P < 0.01) at puberty and had a greater 6-week (P < 0.01) but not 12-week (P = 0.96) pregnancy rate. Enhanced nutrition resulted in a younger age at puberty but had no effect on 12-week pregnancy rate. Dam but not sire breed affected 12-week pregnancy rate.
... Data from Location 2 were collected on a springcalving herd of composite Red Angus × Simmental females. Overwinter treatments evaluated over time included developing heifers to 50 and 55% of mature BW by breeding (Martin et al., 2008) and developing heifers on upland winter range and corn residue Summers et al., 2014). Heifers were exposed to bulls for 45 d at a bull-to-heifer ratio of 1:25. ...
... Pubertal status at the start of breeding was determined by evaluating progesterone concentration in 2 blood samples (8 to 10 mL/sample) collected via coccygeal venipuncture 9 to 11 d apart before initiation of estrus synchronization or the start of the breeding season based on procedures previously reported for Locations 1 , 2 (Martin et al., 2008), and 3 (Roberts et al., 2009). A progesterone concentration ≥ 1 ng/mL in either sample collected for each heifer was interpreted to indicate ovarian luteal activity. ...
Heifer records were retrospectively evaluated to see if Julian birthdate, cycling status prior to breeding, and body weight collected from weaning through final pregnancy diagnosis differed when heifers were categorized by 5 different approaches: 1) pubertal status prior to estrous synchronization, 2) whether or not detected in estrus at AI, 3) heifers impregnated by AI vs all other heifers, 4) final pregnancy status, and 5) a 5-way classification accounting for AI and pregnancy status (AI pregnant, heifers subjected to AI that subsequently conceived to bull, heifers not AI that were impregnated by bull, heifers subjected to AI that were not pregnant, heifers not AI and not pregnant). Collectively, results support the concept that earlier birth in the calving season and greater preweaning growth are associated with desirable reproductive response in replacement beef heifers.
... Data from Location 2 were collected on a springcalving herd of composite Red Angus × Simmental females. Overwinter treatments evaluated over time included developing heifers to 50 and 55% of mature BW by breeding (Martin et al., 2008) and developing heifers on upland winter range and corn residue Summers et al., 2014). Heifers were exposed to bulls for 45 d at a bull-to-heifer ratio of 1:25. ...
... Pubertal status at the start of breeding was determined by evaluating progesterone concentration in 2 blood samples (8 to 10 mL/sample) collected via coccygeal venipuncture 9 to 11 d apart before initiation of estrus synchronization or the start of the breeding season based on procedures previously reported for Locations 1 , 2 (Martin et al., 2008), and 3 (Roberts et al., 2009). A progesterone concentration ≥ 1 ng/mL in either sample collected for each heifer was interpreted to indicate ovarian luteal activity. ...
Data collected for 10 or more years at the West Central Research and Extension Center, North Platte, NE (n = 1,104); the Gudmundsen Sandhills Laboratory, Whitman, NE (n = 1,333); and the USDA, ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT (n = 1,176) were retrospectively analyzed to evaluate growth and reproductive performance of beef heifers classified by pubertal status before first breeding. Concentrations of progesterone in serum from 2 blood samples collected 9 to 11 d apart before the breeding season classified heifers as pubertal (progesterone ≥ 1.0 ng/mL in 1 or both samples) or nonpubertal (progesterone < 1.0 ng/mL in both samples). Average date of birth was earlier (P < 0.06) and proportion born in the first 21 d of the calving season was 10 to 20 percentage points greater for heifers that were pubertal at the start of breeding compared with heifers not pubertal by the start of breeding. Heifers that were pubertal by the start of breeding were 7 to 10 kg heavier (P < 0.01) and 1 cm taller (P < 0.01) at weaning than heifers not pubertal by the start of breeding. Differences in BW persisted through the start of breeding to pregnancy diagnosis. Heifers that achieved puberty by the start of breeding had greater (P < 0.05) feed intake and G:F during postweaning development and had greater (P < 0.01) LM area and fat thickness over the LM at approximately 1 yr of age compared with heifers not pubertal by the start of breeding. Heifers that achieved puberty before the start of breeding had greater (P < 0.01) ADG from birth to weaning but slower (P < 0.10) rates of gain from the start of breeding through pregnancy diagnosis. Pregnancy rate was greater (P < 0.01) for heifers that were pubertal at the start of breeding. In heifers that became pregnant, those that were pubertal before the start of breeding calved earlier (P < 0.01), with a greater (P < 0.01) percentage calving in the first 21 d of calving than heifers not pubertal at the start of breeding. Calves from heifers that achieved puberty before the start of breeding were heavier at weaning (P < 0.01) than calves from heifers that had not achieved puberty by the start of breeding. In summary, heifers that failed to achieve puberty by the start of breeding were less desirable for several traits evaluated. Based on these results, implementing feeding strategies to increase the proportion of heifers that achieve puberty before first breeding could result in propagation of undesirable characteristics. © 2017 American Society of Animal Science. All rights reserved.
... The pattern of growth of beef and dairy cattle can be related to the efficiency of the production system and the longevity of the cow (Engelken 2008). The degree of maturity of a heifer [bodyweight (BW) related to mature weight] is used to estimate its sexual maturity and different thresholds are currently being discussed as optimal for first matings in beef heifers (Martin et al. 2008;Stockton et al. 2014;Titterington et al. 2015). Therefore, accurate knowledge concerning the growth of females of a breed in a given production system could be used to manage them to achieve a desired degree of maturity at key management events, such as first mating. ...
... This animal variation in mature BW could be explained by genetic and environmental causes. The assumption that all cows have the same (breed average) mature weight leads to deviations from the actual maturity index of heifers and may explain in part the diverse results Growth curves in beef cattle Animal Production Science found in evaluation of effects of the reduction of BW at first conception (Patterson et al. 1992;Martin et al. 2008). Recently, Stockton et al. (2013) proposed the use of measurable physical characteristics to forecast beef heifer mature BW and maturity. ...
The objective of this study was to compare the ability of Basis spline (B-spline) models and five non-linear functions (Richards, Brody, Von Bertalanffy, Gompertz and Logistic) to describe the growth of females of a beef cattle breed and predict cow mature weight (A). Random regression models that included animal variation within function parameters were fitted using mixed model procedures. Comparisons were made among these functions for goodness of fit, standardised residuals and biological interpretability of the growth curve parameters. The B-spline function showed the best goodness of fit and within non-linear functions, the Richards and Von Bertalanffy functions estimated bodyweight at different periods accurately. The method of fitting the residual variance that provided the best goodness of fit in the model was the constant plus power variance function. The Richards function was found to be the best non-linear function and was compared with the B-spline function to predict mature weight. When the A parameter was estimated using fixed effects, it had a low correlation with the actual mature weight of the cow and the use of this estimate yielded no more gain in predictive accuracy of mature weight than the use of average breed mature weight. When A was estimated using fixed and random effects, it had a moderate correlation with actual mature weight for the B-spline and Richards functions. The use of both types of effects to estimate the maturity index reduced the error compared with the use of average mature weight, especially for the B-spline function, which is recommended as the best function to describe animal growth and predict mature weight.
... Previous data recommends that heifers reach 65% of their mature BW by the time of breeding (Lamond, 1970;Patterson et al., 1992); however, more recent studies have shown that heifers at 50 to 55% mature BW can successfully conceive and retain the pregnancies (Funston and Deutscher, 2004;Martin et al., 2008;Larson et al., 2009). Percent of mature BW be- fore synchronization in this study differed between years (P < 0.0001) and were 53, 59, and 51% of an expected 544-kg mature weight before synchronization in yr 1, 2, and 3, respectively. ...
... The increase in AI pregnancy rates observed in yr 2 could be due to the increase in heifer BW before the onset of the breeding season. However, several recent studies have demonstrated no reduction in reproductive performance in heifers developed to 50 to 58% of mature BW by breeding (Funston and Deutscher, 2004;Martin et al., 2008;Funston et al., 2012;Lardner et al., 2014). In agreement with those reports, this study provides evidence that postweaning development of heifers to achieve approximately 55% of mature BW before breeding did not negatively affect reproductive performance. ...
Stockpiled tall fescue can provide adequate winter forage for beef cattle, although unsupplemented replacement heifers may display marginal performance before breeding. The objective of this study was to determine if protein supplementation and/or additional forage improves growth and reproductive performance of replacement heifers grazing stockpiled fescue. Cattle averaging 272 ± 1.59 kg were stratified by BW and then randomly assigned to 1 of 4 plots within a pasture replication. Treatment combinations were assigned in a 2 × 2 factorial arrangement and included 1) a conservative forage allocation (“normal,” targeting 85% forage use) and mineral supplement (normal forage allocation with mineral supplement [FM]), 2) normal forage allocation with protein tub (FT), 3) more liberal forage allocation (“extra,” targeting 70% forage use) and mineral supplement (extra forage allocation with mineral supplement [EM]), and 4) “extra forage allocation with protein tub (ET). Treatments were administered for 8 wk from early November to early January. Heifers were fed fescue hay for 1 wk before breeding in late January. Heifers were synchronized with the 7-d CO-Synch + controlled internal drug release device protocol and inseminated in late January. Heifers were checked for pregnancy by ultrasonography at 35 and 90 d after AI. Main and interaction effects between the 2 treatments were determined. Total supplement intake was greater for protein tub than mineral supplement (0.36 vs. 0.11 kg•heifer–1•d–1, respectively; P < 0.0001), and the additional dietary protein in the tub groups resulted in greater serum urea N concentrations (P < 0.0001; 8.15 vs. 10.4 mg/dL for mineral and protein tub, respectively). Forage utilization efficiency was greater for normal than extra forage allocation (74.7 vs. 65.8%, respectively; P < 0.0001). Main effects of both treatments on ADG were significant (P < 0.0001; 0.28, 0.43, 0.43, and 0.51 kg•heifer–1•d–1for FM, FT, EM, and ET, respectively). There was an interaction effect of the 2 treatments on change in BCS (P < 0.05; 0.12, 0.10, 0.18, and 0.31 for FM, FT, EM, and ET, respectively). Reproductive tract scores, pelvic area, and AI pregnancy rates were not different between treatments (P > 0.05). Overall, feeding a protein supplement or providing extra forage increased gain and interacted to increase BCS but did not have an effect on reproductive performance. Supplementing with protein and providing extra forage are strategies that can increase gain in heifers, which could aid heifers in reaching puberty before estrous synchronization. © 2016 American Society of Animal Science. All rights reserved.
... Previous data recommends that heifers reach 65% of their mature BW by the time of breeding (Lamond, 1970;Patterson et al., 1992); however, more recent studies have shown that heifers at 50 to 55% mature BW can successfully conceive and retain the pregnancies (Funston and Deutscher, 2004;Martin et al., 2008;Larson et al., 2009). Percent of mature BW be- fore synchronization in this study differed between years (P < 0.0001) and were 53, 59, and 51% of an expected 544-kg mature weight before synchronization in yr 1, 2, and 3, respectively. ...
... The increase in AI pregnancy rates observed in yr 2 could be due to the increase in heifer BW before the onset of the breeding season. However, several recent studies have demonstrated no reduction in reproductive performance in heifers developed to 50 to 58% of mature BW by breeding (Funston and Deutscher, 2004;Martin et al., 2008;Funston et al., 2012;Lardner et al., 2014). In agreement with those reports, this study provides evidence that postweaning development of heifers to achieve approximately 55% of mature BW before breeding did not negatively affect reproductive performance. ...
Stockpiled tall fescue can provide adequate winter forage for beef cattle, although unsupplemented replacement heifers may display marginal performance before breeding. The objective of this study was to determine if protein supplementation and/or additional forage improves growth and reproductive performance of replacement heifers grazing stockpiled fescue. Cattle averaging 272 ± 1.59 kg were stratified by BW and then randomly assigned to 1 of 4 plots within a pasture replication. Treatment combinations were assigned in a 2 × 2 factorial arrangement and included 1) a conservative forage allocation ("normal," targeting 85% forage use) and mineral supplement (normal forage allocation with mineral supplement [FM]), 2) normal forage allocation with protein tub (FT), 3) more liberal forage allocation ("extra," targeting 70% forage use) and mineral supplement (extra forage allocation with mineral supplement [EM]), and 4) "extra forage allocation with protein tub (ET). Treatments were administered for 8 wk from early November to early January. Heifers were fed fescue hay for 1 wk before breeding in late January. Heifers were synchronized with the 7-d CO-Synch + controlled internal drug release device protocol and inseminated in late January. Heifers were checked for pregnancy by ultrasonography at 35 and 90 d after AI. Main and interaction effects between the 2 treatments were determined. Total supplement intake was greater for protein tub than mineral supplement (0.36 vs. 0.11 kg·heifer·d, respectively; < 0.0001), and the additional dietary protein in the tub groups resulted in greater serum urea N concentrations ( < 0.0001; 8.15 vs. 10.4 mg/dL for mineral and protein tub, respectively). Forage utilization efficiency was greater for normal than extra forage allocation (74.7 vs. 65.8%, respectively; < 0.0001). Main effects of both treatments on ADG were significant ( < 0.0001; 0.28, 0.43, 0.43, and 0.51 kg·heifer·d for FM, FT, EM, and ET, respectively). There was an interaction effect of the 2 treatments on change in BCS ( < 0.05; 0.12, 0.10, 0.18, and 0.31 for FM, FT, EM, and ET, respectively). Reproductive tract scores, pelvic area, and AI pregnancy rates were not different between treatments ( > 0.05). Overall, feeding a protein supplement or providing extra forage increased gain and interacted to increase BCS but did not have an effect on reproductive performance. Supplementing with protein and providing extra forage are strategies that can increase gain in heifers, which could aid heifers in reaching puberty before estrous synchronization.
... The pattern of growth of beef and dairy cattle can be related to the efficiency of the production system and the longevity of the cow (Engelken 2008). The degree of maturity of a heifer [bodyweight (BW) related to mature weight] is used to estimate its sexual maturity and different thresholds are currently being discussed as optimal for first matings in beef heifers (Martin et al. 2008;Stockton et al. 2014;Titterington et al. 2015). Therefore, accurate knowledge concerning the growth of females of a breed in a given production system could be used to manage them to achieve a desired degree of maturity at key management events, such as first mating. ...
... This animal variation in mature BW could be explained by genetic and environmental causes. The assumption that all cows have the same (breed average) mature weight leads to deviations from the actual maturity index of heifers and may explain in part the diverse results Growth curves in beef cattle Animal Production Science found in evaluation of effects of the reduction of BW at first conception (Patterson et al. 1992;Martin et al. 2008). Recently, Stockton et al. (2013) proposed the use of measurable physical characteristics to forecast beef heifer mature BW and maturity. ...
The objective of this study was to compare the ability of Basis spline (B-spline) models and five non-linear functions (Richards, Brody, Von Bertalanffy, Gompertz and Logistic) to describe the growth of females of a beef cattle breed and predict cow mature weight (A). Random regression models that included animal variation within function parameters were fitted using mixed model procedures. Comparisons were made among these functions for goodness of fit, standardised residuals and biological interpretability of the growth curve parameters. The B-spline function showed the best goodness of fit and within non-linear functions, the Richards and Von Bertalanffy functions estimated bodyweight at different periods accurately. The method of fitting the residual variance that provided the best goodness of fit in the model was the constant plus power variance function. The Richards function was found to be the best non-linear function and was compared with the B-spline function to predict mature weight. When the A parameter was estimated using fixed effects, it had a low correlation with the actual mature weight of the cow and the use of this estimate yielded no more gain in predictive accuracy of mature weight than the use of average breed mature weight. When A was estimated using fixed and random effects, it had a moderate correlation with actual mature weight for the B-spline and Richards functions. The use of both types of effects to estimate the maturity index reduced the error compared with the use of average mature weight, especially for the B-spline function, which is recommended as the best function to describe animal growth and predict mature weight.
... Furthermore, it has been reported heifers fed to 51 vs. 57% mature BW showed no difference in attaining puberty. However, heifers developed on corn residue had a reduced percentage that reached puberty compared with winter range or drylot (Martin et al., 2008). Post-weaning management systems can significantly affect progeny development as various rates of gain post-weaning have been shown to affect age at puberty and fertility in heifers (Patterson et al., 1992). ...
ABSTRACT: A study was conducted with the objective to determine the rumen microbiome and fermentation parameters of three ruminally cannulated Angus-crossbred heifers (232 + 12 kg BW) on dormant native rangelands over one year. We hypothesize that as seasons of the year change so will diet quality, rumen fermentation end products and bacterial populations present in the rumen. Heifers were maintained on native range and supplemented 20% CP range cube. Ruminal fluid was collected from April, 2016 to February, 2017 approximately every two to three months for ruminal ammonia, VFA, and bacterial population composition. Amplification and sequencing of the V4 hypervariable region of the 16S rRNA gene using the Illumina MiSeq. Bacteroidetes (43.4%) and Firmicutes (40.5%) were the major phyla throughout the sampling period. Firmicutes differed by day with the greatest population occurring February (45.8 + 2.2%), while Bacteroidetes did not differ by sampling day. The predominant genera throughout study remained Prevotella (17.4%) and Bacteroides (9.3%) and did not differ by sampling day (P > 0.15). Total VFA concentrations (P < 0.01) and acetate:propionate (P < 0.01) increased for the duration of the study. Ammonia levels differed by sampling day with the greatest level occurring during February (17.0 + 1.4%). These data shows the rumen fermentation parameters and microbiome are influenced by the varying diet quality that occurs on native rangelands.
Key words: Ruminal ammonia, Microbiome, Rangeland
... This approach has been used over several decades, primarily feeding heifers in intensive drylot systems to achieve or exceed a target BW, in order to alternative extensive systems that use less feed and 004; Roberts et al. 2009). Other studies have demonstrated that heifers reaching less than 58% of mature BW by breeding do not display impaired reproductive performance (Martin et al. 2008;Funston et al. try, exceeding heifer maintenance and gestation nutrient requirements will increase overall development costs and reduce net returns for beef producers. In western Canada, beef producers are moving from conventional drylot, where cattle during winter months, to the adoption of extensive wintering grazing systems (Van De Kerckhove et al. 2011;Kelln et al. 2011: Krause et al. 2013. ...
Proper development of replacement beef heifers is critical and needs to be accomplished at lower costs without sacrificing reproductive performance. The current recommendations indicate heifers should reach approximately 60-65% of mature body weight (MBW) at breeding for successful reproduction. Meeting heifer maintenance and gestation nutrient requirements are getting more economically challenged for beef producers in western Canada. Therefore, producers are moving from drylot development systems where cattle are housed and fed in pens to the adoption of extensive grazing systems in field paddocks. The most commonly used extensive dormant season grazing system in western Canada is grazing forage bales in field paddocks. This report suggested that through breeding heifers at the 55% of mature BW, about $80 per heifer can be saved without impaired reproductive performance. The document further suggested that bale grazing systems are viable alternatives to decrease ($12/head) heifer development cost.
... However, heifers bred on their third oestrus in that study were 375 days of age, whereas heifers bred on their first oestrus were only 322 days of age, thus confounding the interpretation of the results (Endecott et al. 2013). Heifers developed to a lighter weight at breeding (51% v 57% of estimated mature bodyweight) resulted in a lower pubertal rate at the start of breeding and more open heifers at the end of the breeding season and an extended calving pattern (Martin et al. 2008). In a recent study conducted by our own group (Heslin et al. 2017), heifers (,8 months old at start) gained either 0.5 or 1 kg day À1 over a 145-day differential winter feeding period, which resulted in 9% and 31% of heifers pubertal at the onset of the breeding season respectively. ...
Advancing the age at which puberty and subsequent sexual maturation is attained in cattle is central to the reproductive and economic efficiency of both beef and dairy production systems worldwide. Onset of puberty in both male and female cattle is regulated by a complex network of biochemical processes and involves interaction among many key metabolic, neuroendocrine and reproductive tissues. Although our understanding of the biochemical interplay that conditions and eventually triggers the pubertal process has improved in recent years, much of the intricate mechanistic detail still eludes us. Environmental factors, such as nutritional management, as well as the genetic makeup of the animal undoubtedly affect the timing of puberty in cattle. In particular, there is now overwhelming evidence to support the importance of early life nutrition in regulating the timing of puberty in both bulls and heifers. For both genders, there is significant evidence that an improved metabolic status, early in calfhood, advances maturation of the hypothalamic- pituitary-gonadal axis, therefore facilitating earlier sexual development. Although advancing sexual maturation is a desirable goal, it is important that any strategy used does not impinge upon normal gametogenesis or postpubertal fertility potential. To this end, the aim of this review is to discuss the underlying biology of puberty in cattle with particular emphasis on the role of nutritional management during early calfhood in: (1) advancing the maturity of the hypothalamic- pituitary-gonadal axis; and (2) implications for the quality of gametes and subsequent fertility.
... To achieve a statistical difference in AI pregnancy rate between RANGE and DLLO heifers, an additional 3 yr with 25 heifers/treatment each yr would be necessary. Previous research has reported similar final pregnancy rates in heifers restricted in ADG postweaning (Funston and Deutscher, 2004;Martin et al., 2008). Although DLHI heifers had the lowest ADG following AI, BW at first pregnancy diagnosis was greatest (P = 0.03) for DLHI heifers compared with RANGE and CR. ...
A 3-yr study utilized 300 Angus-based, spring-born heifers to evaluate postweaning heifer development systems on gain, reproductive performance, and feed efficiency as a pregnant heifer. Heifers were blocked by BW and randomly assigned to graze corn residue (CR), upland range (RANGE), or were fed 1 of 2 diets in a drylot differing in energy levels: high (DLHI) or low (DLLO). Heifers developed on DLHI and DLLO were managed within the drylot for 166 d in yr 1, 150 d in yr 2, and 162 d in yr 3. Heifers developed on RANGE grazed winter range for an equivalent amount of days each yr as the DLHI and DLLO heifers. Heifers assigned to CR grazed for 103 d in yr 1, 84 d in yr 2, and 97 d in yr 3 before being transported to graze winter range for the remainder of the treatment period. All heifers were managed as a single group following the treatment period. Artificial insemination and natural mating were utilized during breeding. Percent of mature BW prior to the breeding season was greater (P = 0.02) for DLHI (67%) compared with RANGE (59%) and CR (58%). Pregnancy rates to AI were not different (P = 0.51) among treatments (59 ± 6%), and final pregnancy rates were also not different (87 ± 4%, P = 0.54). A subset of AI-pregnant heifers from each treatment were placed in a Calan gate feeding system. Heifers were allowed a 20-d acclimation period before beginning the 90 d trial at approximately 170 d in gestation. Heifers were offered ad libitum hay; amount offered was recorded daily and orts collected weekly. Initial BW was not different (P = 0.58) among treatments (459 ± 11 kg). Body weight at the end of the trial (497 ± 17 kg) was also not different (P = 0.41). Intake was not different (P = 0.33), either as DMI (10.00 ± 1.07 kg) or residual feed intake (0.018 ± 0.190). There was no difference in ADG (P = 0.36, 0.42 ± 0.23 kg/d) among treatments. Although the total development cost was not different among treatments (P = 0.99), there was a $41 difference (P < 0.01) between the mean of the most expensive diet (DLHI) and the mean of the two least expensive diets (CR and RANGE). Developing heifers to a greater prebreeding BW did not influence subsequent AI or overall pregnancy rates or feed efficiency as a pregnant heifer. © 2017 American Society of Animal Science. All rights reserved.
... Age and BW at first puberty (of those heifers cycling before breeding) were not affected by treatment (P ≥ 0.70); the percentage of heifers determined to be cyclic before breeding was 76% for MON, 64% for CNTRL, and 65% for BAMB. Across treatments, the heifers reached puberty at an average BW of 304 kg, which is approximately 60% of their average estimated mature BW and was greater than the 51% of mature BW at breeding observed by Martin et al. (2008) and the 56% of mature BW at breeding observed for extensively raised heifers by Funston and Larson (2011). Ionophores and ruminally active antibiotic growth promoters function by increasing the production of propionate and decreasing the acetate:propionate ratio, increasing DM and protein digestibility, and increasing gluconeogenesis and glucose turnover (Schelling, 1984), leading to the hypothesis that feeding MON and BAMB would increase prebreeding puberty rates. ...
Medicated feed additives have been shown to increase BW gain and decrease age at puberty; therefore, heifers were provided nonmedicated control (CNTRL), bambermycins (BAMB, Gainpro, Huvepharma Inc., Sofia, Bulgaria), or monensin (MON, Rumensin, Elanco Animal Health, Greenfield, IN) supplements to determine effects on growth performance and reproductive development. Spring-calving (block 1; n = 70 heifers; BW = 208 ± 21.7 kg; age = 231 ± 17.0 d) and fall-calving (block 2; n = 72 heifers; BW = 225 ± 31.7 kg; age = 276 ± 12.8 d) heifers were allotted to treatments [n = 4 groups in CNTRL and 5 groups in BAMB and MON (block 1), 4 groups per treatment (block 2)] by breed, BW, and source. Heifers in block 1 grazed tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] for 188 d; heifers in block 2 grazed bermudagrass (Cynodon dactylon) pasture and tall fescue for 161 d. The BW at breeding and ADG of CNTRL (323 ± 4.8 kg and 0.68 ± 0.0167 kg/d, respectively) was less (P ≤ 0.04) than medicated, yet MON (346 ± 4.6 kg and 0.73 ± 0.0163 kg/d) and BAMB (344 ± 4.6 kg and 0.74 ± 0.0163 kg/d) did not differ (P ≥ 0.69). Prebreeding reproductive tract scores (3.5 ± 0.60), cycling activity (61 ± 12.3%), and AI (30 ± 12.3%) and total pregnancy rates (82 ± 11.5%) did not differ (P ≥ 0.25) among treatments. This experiment indicates that BAMB and MON effectively increased growth performance of heifers but did not affect reproductive development or pregnancy rates.
... Additionally, early reports would suggest heifers fed a lower plane of nutrition during the development period should experience a greater incidence and severity of dystocia (Bellows and Short, 1978; Patterson et al., 1991). However, Martin et al., (2008) reported no differences in calf birth BW or the proportion of heifers requiring assistance between treatments. They concluded the development costs for a heifer developed to 50% mature BW prior to the breeding season resulted in $17 cost reduction as opposed to heifers developed to 55% mature BW. ...
The objective of an invited review and four experiments was to evaluate production implications and economic efficiencies of beef systems strategies involving calving date selection, utilization of reproductive technology, and post-weaning management of heifers and steers. The invited review in chapter II considers factors that influence a producer’s decision on when to calve beef females. The calving date decision impacts the entire beef production cycle and must take into account any environmental conditions, available resources, and cite specific advantages and/or disadvantages. Understanding the importance of varying physiological state and nutrient demands associated with lactation and gestation is critical to optimizing calving date. Calving systems vary across geographic regions. The associated differences in management strategies, along with economic drivers, contribute to the complexity of the calving date decision. Chapter III evaluates the effects of overwinter nutrition on subsequent May calving cow performance. Supplemented cows had increased (P < 0.01) BCS and BW change over winter treatment period compared to unsupplemented cows. Cows grazed either dormant upland range or meadow during the winter period. Pasture treatment had an effect on winter BW gain, pre-calving BW, lactation BW gain, pregnancy rate, as well as progeny birth and weaning BW. Pregnancy rate (P = 0.05) and calf birth BW (P = 0.03) were lower, and calf WW tended (P = 0.06) to be lower for cows that grazed dormant range without supplement. Chapter IV compares a modified fixed-time AI protocol to fixed-time AI. Heifer reproductive performance at both AI conception and overall conception rate was similar (P < 0.05) in both treatments. Chapter V evaluates the effects of a Revalor G implant on reproduction and growth performance of 12 mo old beef heifers. Implanting heifers reduced conception rate by 18 percentage points in implanted heifers, but resulted in a 6 kg growth advantage over non-implanted heifers. Chapter VI compares four supplement sources on growth performance of steers grazing irrigated corn residue. Supplementing with dried distiller grains and SoyPass/SBM blend provided sufficient CP in the form of RDP and RUP for steers to gain at rates above 0.45 kg/d, while supplementing with corn grain and corn grain + RDP resulted in gains far below (< 0.2 kg/d) other treatments. Growing steers will require protein supplementation in the form of both RUP and RDP in order to optimize growth performance while grazing corn residue.
Advisors: Richard N. Funston and Jim C. MacDonald
... weeks of age, respectively) with rapid testicular growth rates between 22 and 44 weeks of age and better characteristics of ejaculate compared with control bulls. Treatment with melengestrol acetate (MGA) in prepubertal bovine heifers for 14 days did not reduce age at puberty, nor did it improve proportion of heifers pubertal before breeding, pregnancy rate, calving date, calf weaning weight and second breeding season pregnancy rate [34]. ...
... These results are consistent with previous research indicating pre-weaning growth exerts a greater influence on puberty than post-weaning growth (Patterson et al., 1992;Roberts et al., 2009). This also agrees with previous research reporting ADG prior to breeding has minimal impact on pubertal status and pregnancy rates (Funston and Deutscher, 2004;Martin et al., 2007;Funston and Larson, 2011;Larson et al., 2011). ...
Three experiments were conducted to evaluate whether pubertal status and number of estrous cycles prior to breeding influences pregnancy rate in beef heifers. Pubertal heifers were heavier and older at the start of breeding and had greater AI and overall pregnancy rate than non-pubertal heifers. Second season pregnancy rate was greater for heifers reaching puberty prior to first breeding and for heifers having ≥ 2 estrouscycles prior to breeding compared with non-pubertal heifers. Pregnancy rate was greater for heifers achieving puberty prior to breeding; however, earlier onset of puberty did not significantly improve first pregnancy rates.
... Arthur et al. (2005) found no difference in pregnancy rate but found that low RFI cows calved 5 d later (P = 0.07) than high RFI cows. The lower pregnancy rate in low-RFI group in the current study should be interpreted with caution given the relatively small number of animals (n = 20/RFI group), however it may be speculated that any over conditioning in low-RFI group may result in reproductive failure (Martin et al., 2008). In the current study, the average pregnancy rate was 90.8% across all heifer groups. ...
The objective of this study was to compare two heifer groups with differing residual feed intake (RFI) ranking (feed efficient or low-RFI and feed inefficient or high-RFI) with a conventional industry selected (control group; CON) group of heifers for winter feeding performance, feeding behavior, and subsequent reproductive efficiency. The three heifer groups (n = 20/group; initial BW = 322 ± 2.9 kg) were fed a forage-based (90% processed grass-legume hay and 10% rolled barley) diet (14.7% CP; 53.7% TDN) for 78 d, and individual animal DMI and feeding activity were determined. The RFI was calculated for each animal using a model which included ADG, mid-metabolic BW (BW 0.75), and DMI. Heifer groups did not differ (P > 0.05) in final BW (391 ± 3.5 kg), DMI (9.7 ± 0.12 kg), final BCS (2.6 ± 0.20 kg), feeding event duration (FD; 174 ± 3.8 min/d), eating rate (ER; 0.056 ± 0.001 kg/min), and feeding frequency (FF; 144 ± 3.8 events/d). As well, RFI was-0.09 ± 0.15,-0.33 ± 0.12, and 0.42 ± 0.13 kg/d for CON, low-RFI, and high-RFI groups, respectively. The low-RFI group (108.5 ± 6.2 min/d) did not differ (P > 0.05) from CON (115.5 ± 6.2 min/d), but was lower (P < 0.05) than high-RFI heifers (142.3 ± 7.9 min/d) in feeding event head-down time. While low-RFI heifers tended to have lower FD (161.7 ± 4.4 min/d; P < 0.1) than high-RFI group (190.3 ± 7.3 min/d), FD for low-RFI was similar (P > 0.05; 171 ± 6.2 min/d) to CON heifers. Low-RFI group (10.4 ± 0.32) tended to have lower (P < 0.1) feed conversion ratio (FCR) than either CON or high-FRI heifers, 11.4 ± 0.34 and 11.25 ± 0.31, respectively. The CON heifers (1746 ± 14.6 kg/200 d) were numerically (P > 0.05) greater than low-RFI heifers (1689 ± 38.8 kg/200 d), but were numerically lower (P > 0.05) than high-RFI heifers (1856 ± 37.4 kg/200 d) in consumed feed (DM basis) for entire development period (200 d). Based on first-calf pregnancy rate, the heifer groups can be ranked as follows: low-RFI (80%) < CON (93%) < high-RFI heifers (100%). In summary, feed efficient heifers with increased feed efficiency may not result in improved reproductive performance, and further research is warranted.
... Previous research reports late gestation protein supplementation influences multiparous cow progeny performance, carcass quality, and health (Stalker et al., 2006(Stalker et al., , 2007Martin et al., 2008;Mulliniks et al., 2008;Larson et al., 2009). These results support the fetal programming hypothesis, which suggests that maternal environment during gestation can influence progeny postnatal growth and health (Barker et al., 1993). ...
A 3-yr study using primiparous crossbred beef heifers ( = 114) was conducted to determine the effects of protein supplement during late gestation on progeny performance and carcass characteristics. Pregnant heifers were stratified by heifer development system, initial BW, and AI service sire and placed in an individual feeding system. Heifers were offered meadow hay (8 to 11% CP) from early November to mid-February and provided no supplement (CON; = 37), 0.83 kg/d (DM basis) of a dried distillers grains with solubles-based supplement (HI; = 39), or 0.83 kg/d (DM basis) of a dried corn gluten feed-based supplement (LO; = 38). Supplements were designed to be isonitrogenous (28% CP) and isocaloric but to differ in RUP with HI (59% RUP) having greater levels of RUP than LO (34% RUP). After the individual feeding period, heifers were placed in a drylot for calving. All heifers were bred using a fixed-timed AI protocol and pairs were moved to a commercial ranch in the Nebraska Sandhills for summer grazing. Calf weaning BW did not differ ( = 0.14) based on maternal diet. However, feedlot entry BW was greater ( = 0.03) for HI compared with CON calves. Average daily gain during the initial feedlot phase tended ( = 0.10) to be greatest for calves born to CON dams and lowest for calves born to LO dams. However, overall ADG was similar ( = 0.50) for the entire feedlot period. Residual feed intake during the reimplant and total feeding period was improved in calves born to supplemented dams in yr 2 and 3 compared with calves born to CON dams. There was no difference in final BW among treatments ( = 0.71). Hot carcass weight was similar ( = 0.72) among treatments; however, steers had greater ( < 0.01) HCW than heifers. Furthermore, percent empty body fat and 12th rib fat thickness were lowest ( = 0.05 and = 0.04) for calves born to LO dams. Tenderness measured by Warner-Bratzler shear force was increased ( = 0.03) in longissimus samples from calves from CON dams compared to calves from LO dams. Similarly, crude fat levels tended to be greater ( = 0.07) for calves from CON dams compared with calves from LO dams. Based on these data, providing RUP supplements, similar to those used in this study, to primiparous heifers in late gestation consuming ad libitum grass hay resulted in increased initial feedlot BW for HI compared to CON calves, improved feed efficiency, and altered carcass characteristics in calves born to supplemented compared with CON dams.
... The use of underdeveloped heifers, heifers that are only ~52 % of mature BW, is a unique, unplanned factor in this experiment and represents a common scenario in the US beef industry. This level of heifer development is within a range of recent research reports that developed heifers to between 50 and 55% of mature BW and reduced development cost without reductions in total breeding pregnancy rates (Martin et al., 2008;Roberts et al., 2009). The lack of differences in final BW and BCS and overall BW gain during supplementation indicated the supplements were isocaloric as formulated. ...
Research involving fat supplementation to heifers has shown positive reproductive effects, but the effect of lipid composition has had little investigation. Heifers (n = 118) were blocked by age, breed, and BW and pen-fed alfalfa hay. Heifers were individually fed 1 of 3 isocaloric supplements: control (CON) or either half the CON diet with 0.2 kg of a rumenprotected unsaturated fatty acid source (USFA) or a rumen-protected saturated fatty acid source (SFA) fed 5 d/wk. Heifers received treatments for 3 wk before starting the 7-d controlled intravaginal drug release estrus synchronization protocol. Heifers remained on treatment for 28 d after AI. Pregnancy was determined at d 30 post-AI via transrectal ultrasonography and by rectal palpation at 150 d post-AI. Serum progesterone and leptin were measured by RIA and serum triglycerides; cholesterol was measured by colorimetric procedures. Heifers BW gain during supplementation was similar (P = 0.35) between treatment groups (32 ± 2 kg). Percentage of heifers cycling tended to be less (P = 0.08) for USFA heifers compared with CON and SFA treatments (36 vs. 55 and 56%, respectively). Pregnancy rates by AI of heifers detected in estrus were similar (P = 0.35) between treatments. Serum total and specific fatty acids, cholesterol, and triglycerides were greater (P < 0.05) at d 21 and 56 in fat-supplemented heifers compared with CON heifers. At d 56 of treatment, USFA had greater (P < 0.05) plasma leptin compared with SFA, with CON heifers having further reduced serum leptin concentration. Feeding rumen-protected fats to heifers increased circulating lipid and leptin, but did not influence reproduction rates.
... The increasing gain development method reported in this research investigation relies upon a divergent approach to attain high reproductive success using an increasing gain method and a 50 d breeding season. The data reported herein agrees with results reported by Funston and Deutscher (2004), Martin et al. (2008), andFreetly et al. (2011), indicating that heifers attaining 50% to 57% of mature BW by the start of the breeding season can have similar pregnancy rates as heifers grown to 60% to 65% of mature BW, and is an appropriate extensive, lower-input, less-intense, protocol for transitioning heifers from a March-April calving period to May-June calving period. This protocol is especially valuable, because North American cattlemen are faced with less available experienced labor for calving during the harsh March-April calving period; therefore, cow-calf producers are moving to May-June calving, which is more in synch with when wildlife in the northern Great Plains give birth to their young. ...
A non-traditional forage-based protocol was employed to evaluate replacement heifer growth, fertility, and economics between small frame (SF, 3.50; n = 50) and large frame (LF, 5.56; n = 50) heifers using three increasing gain growth phases. Preceding an 85 d growing-breeding period (Phase 3; P3) the heifers were managed as a common group for Phases 1 and 2 (P1 and P2). During P1, heifers grazed common fields of unharvested corn and corn residue (total digestible nutrients [TDN] 56%) with supplemental hay. For P2, heifers grazed early spring crested wheatgrass pasture (CWG; TDN 62%) that was followed by the final P3 drylot growing and breeding period (TDN 68%). Small frame heifers were lighter at the end of P1 in May and at the start of P3 breeding in August (p = 0.0002). Percent of mature body weight (BW) at the end of P1 (209 d) was 48.7% and 46.8%, respectively, for the SF and LF heifers and the percent pubertal was lower for SF than for LF heifers (18.0% vs 40.0%; p = 0.02). At breeding initiation (P3), the percentage of mature BW was 57.8 and 57.2 and the percentage pubertal was 90.0 and 96.0 (p = 0.07) for the SF and LF heifers, respectively; a 5-fold increase for SF heifers. Breeding cycle pregnancy on days 21, 42, and 63, and total percent pregnant did not differ (p>0.10). In drylot, SF heifer dry matter intake (DMI) was 20.1% less (p = 0.001) and feed cost/d was 20.3% lower (p = 0.001), but feed cost/kg of gain did not differ between SF and LF heifers (p = 0.41). Economically important live animal measurements for muscling were measured in May and at the end of the study in October. SF heifers had greater L. dorsi muscle area per unit of BW than LF heifers (p = 0.03). Small frame heifer value was lower at weaning (p = 0.005) and the non-pregnant ending heifer value was lower for SF heifers than for the LF heifers (p = 0.005). However, the total development cost was lower for SF heifers (p = 0.001) and the net cost per pregnant heifer, after accounting for the sale of non-pregnant heifers, was lower for SF heifers (p = 0.004). These data suggest that high breeding efficiency can be attained among March-April born SF and LF virgin heifers when transitioned to a more favorable May-June calving period through the strategic use of grazed and harvested forages resulting in a lower net cost per pregnant SF heifer.
... Moreover, Nunez-Dominguez et al. (1991) pointed out that the lifetime economic efficiency of beef cows bred for the first time at the age of 15 mo was higher than those bred as 27 mo olds by 6 to 8%, depending on the culling policy. Funston and Deutscher (2004) observed no difference between the pregnancy rates of heifers developed to reach either 53 or 58% of the mature BW, while Martin et al. (2008) found a prebreeding weight as low as 51% of the mature BW to be more effective in terms of costs than development to 57% of the mature BW. However, the latter author pointed out that developing heifers to only 50% of the anticipated mature BW resulted in a low percentage (only 35%) of heifers reaching puberty at the start of the breeding season. ...
The aim of this study was to provide farmers an efficient tool for supporting optimal decisions in the beef heifer rearing process. The complexity of beef heifer management prompted the development of a model including decisions on the feeding level during pre-puberty (age < 10 mo), the time of weaning (age, BW, calendar mo), the feeding level during the reproductive period (age ≥ 10 mo) and time of breeding (age, BW, calendar mo).The model was formulated as 3-level hierarchic Markov process. A founder level of the model has 12 states resembling all possible birth months of a heifer. Based on the birth month information from the founder level, for the indoor season (November to April) and outdoor season (May to October), feeding and breeding costs (natural service cost in the outdoor and artificial insemination cost in the indoor season) were applied. The optimal rearing strategy was found by maximizing the total discounted net revenues from the predicted future productivity of the Polish Limousine heifers defined as the cumulative BW of calves born from a cow calved until the age of five years, standardized on the 210th d of age.According to the modeled optimal policy, heifers fed during the whole rearing period at the ADG of 810 g/d and generally weaned after the maximum suckling period of 9 mo should already be bred at the age of 13.2 mo and BW constituting 55.6% of the average mature BW. Based on the optimal strategy, 52% of all heifers conceived from May to July, and calved from February to April. This optimal rearing pattern resulted in an average net return of EUR 311.6 per pregnant heifer.It was found that the economic efficiency of beef operations can be improved by applying different herd management practices to those currently used in Poland. Breeding at 55.6% of the average mature BW, after a shorter and less expensive rearing period, resulted in an increase in the average net return per heifer by almost 18% compared to the conventional system, in which heifers were bred after attaining 65% of the mature BW. Extension of the rearing period by 2.5 mo (breeding at the age 15.7 mo), due to a pre-pubertal growth rate lowered by 200 g, reduced the average net return per heifer by 6.2% compared to the results obtained under the basic model assumptions.In the future, the model may also be extended to investigate additional aspects of the beef heifer development, such as the environmental impacts of various heifer management decisions.
... However, subsequent research has demonstrated that harvested feed input can be reduced without major adverse effects on reproduction. Recent research indicates heifers reaching <55% of mature BW by breeding have similar reproductive ability to heavier counterparts (Funston and Deutscher, 2004;Martin et al., 2008). However, much of this research has been performed in a dry-lot setting and limited or no data exist comparing development systems using standing forage . ...
The objective of this study was to compare heifer growth and reproductive performance following 2 levels of stockpiled fall forage allowance of orchardgrass (30.5%) and tall fescue (14.1%). Spring born heifers (n = 203, BW = 246 ± 28.9 kg) of primarily Angus background were allocated to 2 grazing treatments during the fall period (Nov. 12 to Dec. 17, yr 1; Nov. 7 to Jan. 4, yr 2; Nov. 7 to Jan. 14, yr 3) each replicated 3 times per year for 3 years. Treatments consisted of daily herbage DM allocation of 3.5 (LO) or 7.0 (HI) % of BW under strip-grazing management. Throughout the winter feeding period mixed grass-legume haylage and soybean hulls were fed. Heifers were grazed as 1 group under continuous stocking after the winter period. Heifers in the LO group gained less than heifers in the HI group during the fall grazing period (0.12 vs. 0.40 kg/d; P < 0.0001). For each 1 percentage unit increase in NDF content of the fall pasture, fall ADG decreased 0.14 kg (P = 0.01). During winter feeding, ADG was 0.30 kg/d and 0.39 kg/d for LO vs. HI heifers, respectively (P = 0.0008). During the spring grazing period (April 16 to May 24, yr 1; April 22 to May 26, yr 2; April 5 to May 16, yr 3), LO heifers had numerically greater ADG than HI heifers (1.38 vs. 1.30 kg/d; P = 0.64). Hip height (122.7 vs. 121.4 cm; P = 0.0055), BCS (5.8 vs. 5.6; P = 0.0057), and BW (356 vs. 335 kg; P < 0.0001) at the end of spring grazing was greater for HI than LO heifers. Heifers in the LO group compensated with greater summer ADG than heifers in the HI group (0.74 vs. 0.66 kg/d; P = 0.03). Total ADG from treatment initiation (November) through pregnancy diagnosis (August) was greater for HI than LO heifers (0.61 vs. 0.55 kg/d; P < 0.001) as was BW at pregnancy diagnosis (415 vs. 402 kg; P = 0.0055). Percentage of heifers reaching puberty by the time of AI was 34% for both groups (P = 0.93). Percentage of heifers becoming pregnant to AI tended (P = 0.13) to be greater for HI (44%) than for LO heifers (32%). Fall ADG across treatment groups affected the probability of a heifer becoming pregnant by AI (P = 0.01). Percentage pregnant by natural service (61% for LO vs. 59% for HI; P = 0.80) and final pregnancy rate (74% for LO vs. 77% for HI; P = 0.61) was not different for the 2 groups. These results indicate that altering fall forage allowance may delay the majority of BW gain until late in heifer development without negatively affecting overall pregnancy rates.
The replacement heifer represents the next generation of genetic progress for the cow herd. Recent surveys indicate that approximately 85% of beef replacement heifers were raised on the operation where they calved. Developing replacement heifers to a genetic specific pubertal weight is crucial to the success of the first breeding season and subsequent productivity. Approximately 30–60 days prior to breeding, heifers should undergo a prebreeding evaluation. Planning for the breeding season should begin early enough to allow time for bull selection (AI or natural service), as well as acquisition and implementation of the estrus synchronization protocol. Heifers calving in moderate condition usually have less dystocia, a shorter postpartum interval, and higher pregnancy rates after their second breeding season. Nutrition prior to parturition can also affect postnatal development of the calf by influencing colostrum quality and quantity. Events crucial to heifer development center on proper selection, nutritional management, breeding season management, and program evaluation.
Infertility is a challenging phenomenon in cattle that reduces the sustainability of beef production worldwide. Here, we tested the hypothesis that gene expression profiles of protein-coding genes expressed in peripheral white blood cells (PWBCs), and circulating micro RNAs in plasma, are associated with female fertility, measured by pregnancy outcome. We drew blood samples from 17 heifers on the day of artificial insemination and analyzed transcript abundance for 10,496 genes in PWBCs and 290 circulating micro RNAs. The females were later classified as pregnant to artificial insemination, pregnant to natural breeding or not pregnant. We identified 1860 genes producing significant differential coexpression (eFDR < 0.002) based on pregnancy outcome. Additionally, 237 micro RNAs and 2274 genes in PWBCs presented differential coexpression based on pregnancy outcome. Furthermore, using a machine learning prediction algorithm we detected a subset of genes whose abundance could be used for blind categorization of pregnancy outcome. Our results provide strong evidence that transcript abundance in circulating white blood cells is associated with fertility in heifers.
Background
Artificial insemination is a preferred breeding method for beef heifers as it advances the genetic background, produces a predictive and profitable calving season, and extends the heifer’s reproductive life span. As reproductive efficiency in heifers is key for the success of beef cattle production systems, following artificial insemination, heifers are exposed to a bull for the remainder of the breeding season. Altogether, up to 95% of heifers might become pregnant in their first breeding season. Heifers that do not become pregnant at the end of the breeding season represent an irreparable economical loss. Additionally, heifers conceiving late in the breeding season to natural service, although acceptable, poses serious losses to producers. To minimize losses due to reproductive failure, different phenotypic parameters can be assessed and utilized as selection tools. Here, we tested the hypothesis that in a group of pre-selected heifers, records of weaning weight, age at weaning, age at artificial insemination, and age of dam differ among heifers of varied reproductive outcomes during the first breeding season.
Results
None of the parameters tested presented predictive ability to discriminate the heifers based on the response variable (‘pregnant to artificial insemination’, ‘pregnant to natural service’, ‘not pregnant’). Heifers categorized with body condition score = 6 and reproductive tract score ≥ 4 had the greatest proportion of pregnancy to artificial insemination (49% and 44%, respectively). Furthermore, it was notable that heifers presenting body condition score = 6 and reproductive tract score = 5 presented the greatest pregnancy rate at end of the breeding season (89%). Heifers younger than 368 d at the start of the breeding season did not become pregnant to artificial insemination. Those young heifers had 12.5% chance to become pregnant in their first breeding season, compared to 87.5% if the heifers were older than 368 days.
Conclusion
Our results suggest that beef heifers with body condition score = 6 and reproductive tract score ≥ 4 are more likely to become pregnant to artificial insemination. Careful assessment should be undertaken when developing replacement heifers that will not reach 12 months of age by the beginning of the breeding season.
Electronic supplementary material
The online version of this article (10.1186/s40104-019-0329-6) contains supplementary material, which is available to authorized users.
Profitability of beef cattle producers can be directly tied to the productive lifespan of a cow. Management decisions influencing heifer nutrition and reproduction play a key role in establishing heifer fertility and longevity. Altering feeding strategies to utilize compensatory growth has been reported to have a positive influence on fertility during the first breeding season; however, there are discrepancies in the literature as to the impact this strategy may have on the proportion of heifers attaining puberty prior to entering their first breeding season. Ultimately, this may affect lifetime productivity as heifers born early in the calving season produce more kilograms of weaned calf over their first 6 calves, as well as, remain in the herd longer than those animals born later in the calving season. Thus, incorporation of reproductive technologies to identify fertile animals or aid in improving conception earlier in the breeding season may improve heifer reproductive performance and longevity. Reproductive tract scores have been utilized to identify animals which are more reproductively mature, increasing the likelihood of successful artificial insemination. Antral follicle counts (AFC), which predict the number of follicles in the ovarian reserve, have not only been reported to have a moderate to high heritability, but have also been used to identify animals with greater reproductive potential. Beef heifers classified as high AFC have greater pregnancy rates and longevity than low AFC heifers. Additionally, maternal diet may play a role in influencing reproductive success and ultimately cow longevity. Improving maternal plane of nutrition has been reported to increase female offspring pregnancy rates. Overall, recent research has provided producers with a variety of methods to optimize animal performance while enhancing reproductive success and longevity to ensure profitability.
Four experiments were conducted to determine the impact of development systems, trace mineral source, and trace mineral supplementation on beef heifers. Experiment 1 utilized 300 Angus-based, spring-born heifers to evaluate postweaning heifer development systems on gain, reproductive performance, and feed efficiency as a pregnant heifer. Heifers were blocked by BW and randomly assigned to graze corn residue, upland range, or were fed 1 of 2 diets in a drylot differing in energy levels: high or low. Heifer development system did not impact AI or final pregnancy rates. Development cost per pregnant heifer was not different among treatments. Furthermore, pregnant heifer feed efficiency was not impacted by development system. In Experiment 2, March-born and May-born crossbred heifers were stratified by BW and randomly assigned to 1 of 2 postweaning treatments from mid-January to mid-April: (1) ad libitum meadow hay and 1.64 kg/d of a 32% CP supplement (HAY) or (2) grazed meadow and 0.41 kg/d of supplement (MDW). March and May-born HAY heifers experienced greater ADG during the treatment period. During the summer period, however, MDW heifers had greater ADG than HAY heifers, likely due to compensatory gain. Heifer development system did not impact pregnancy rate in the March or May replacement heifers; however, March-born heifer pregnancy rate was greater than May-born. The lower pregnancy rate in May heifers may be due to declining forage quality during the late-summer breeding season. In Experiment 3, heifers were synchronized with a 14-d CIDR-prostaglandin F2α protocol and either injected with a trace mineral or received no injection at CIDR insertion. Prior to synchronization, heifers were range developed and offered free-choice mineral. Mineral status prior to mineral treatment did not differ among heifers. The proportion of heifers pregnant within the first 21 d and 33 d of the breeding season was not different nor was overall pregnancy rates. In summary, injectable trace mineral at CIDR insertion 33 d before artificial insemination did not influence reproductive performance in heifers with adequate trace mineral status. In a final study, beef heifers previously managed on 3 separate development systems were stratified by previous development treatment and BW and allocated into 1 of 8 pens per yr. Pens were randomly assigned to 1 of 2 mineral sources, hydroxy (HD) or sulfate (CON). Mineral status was analyzed via two liver biopsies prior to and following the 68-d mineral treatment. Heifer BW, ADG, and reproductive performance was not different in heifers receiving either mineral source treatments. Mineral source treatment did not affect final Mn or Zn concentrations. Liver Cu concentrations were greater for CON than HD heifers at the end of the trace mineral trial; however, all heifers maintained adequate status throughout the study. The difference in Cu status may be due to ruminally insoluble hydroxy Cu allowing thiomolybdate absorption, thus reducing hepatic Cu stores and resulting in decreased Cu status. Advisors: Rick N. Funston and Andrea S. Cupp
The objective of the present study was to evaluate the effects of beef heifer development practices and the influence of season on uterine artery hemodynamics during mid to late gestation. Metrics of uterine artery blood flow (BF) of fall calving and spring calving crossbred beef heifers (n = 27) developed on either a low input (LOW|FALL n = 6; LOW|SPRING n = 6) or a conventional (CON|FALL n = 9; CON|SPRING n = 6) heifer development scheme were evaluated. Heifer body weight (BW) was measured every 30 days, and uterine BF, arterial diameter (AD), pulsatility index (PI), and resistance index (RI) were measured for uterine arteries ipsilateral and contralateral to the conceptus on days 180, 210, and 240 of gestation. Calf birth weight was assessed at parturition. Repeated measures ANOVA was performed. There were significant treatment × season (P = 0.0001) and season × day (P = 0.003) interactions on heifer BW. Main effects of season (P = 0.04) and gestational day (P = 0.0001) were observed on contralateral BF, and there was a season × day interaction (P = 0.03) on ipsilateral BF. As such, there was a season × day interaction on total BF (TBF; P = 0.05) whereby TBF increased as gestation progressed and spring calving heifers displayed increased TBF. However, when adjusted for BW, an additional main effect of treatment was observed (P = 0.0007) in which LOW heifers had increased TBF compared to CON heifers. Correspondingly, LOW heifers displayed increased AD compared to CON heifers, and spring calving heifers had greater AD than fall calving females. There was also a main effect of season on calf birth weight (P = 0.02). It was concluded that developing replacement heifers with low input management schemes does not yield compromised uteroplacental hemodynamics as compared to traditionally developed females when nutrition during gestation is adequate. Furthermore, spring calving two year old heifers have increased uteroplacental BF compared to their fall calving counterparts. Our results imply that producers who seek to decrease development costs by feeding replacements to lighter target breeding weights may do so without compromising mid to late gestation uterine BF when heifers are not nutrient restricted during pregnancy.
The focus of dystocia prevention is primarily directed at first-calf heifers, and the most common cause of dystocia in heifers is fetal–dam disparity. The incidence of calving difficulty is significantly less for mature cows compared with heifers. The use of expected progeny differences (EPDs) in the beef industry has allowed for a more scientifically based path to improvement in traits where EPDs are available. The advantage of using calving ease direct (CED) EPD to decrease dystocia is that it is a direct measurement of differences in percentage of unassisted births between bulls. Studies show that early intervention in cases of dystocia yield more live healthy calves and more live healthy heifers. If CED EPDs are not available, then selecting highly accurate bulls well below breed average for across-breed (AB) birthweight EPD is a reasonable approach.
The replacement heifer represents the next generation of genetic progress for the cow herd. The cost of heifer development must take into account the level of reproductive performance and cash value of the open heifer. Recent surveys indicate that approximately 85% of beef replacement heifers were raised on the operation where they calved. The process of heifer development normally begins at the time of weaning with the initial selection of potential replacements. The health program for the replacement heifer should be targeted against reproductive disease and helps to optimize growth rate. This program should complement the suckling calf vaccination protocol that was administered so that protective immunity is maximized. Once heifers are determined to be pregnant, they need to be managed to calve in moderate body condition. Weight gains need to focus on having the heifers reach approximately 85% of their expected mature weight by the time they calve.
Understanding the biology of heifer maturity and its relationship to calving difficulty and subsequent breeding success is a vital step in building a bio-economic model to identify optimal production and profitability. A limited dependent variable probit model is used to quantify the responses among heifer maturities, measured by a maturity index (MI), on dystocia and second pregnancy. The MI account for heifer age, birth BW, pre-breeding BW, nutrition level, and dam size and age, and is found to be inversely related to dystocia occurrence. On average there is a 2.2% increase in the probability of dystocia with every 1 point drop in the MI, between the MI scores of 50 and 70. Statistically, MI does not directly alter second pregnancy rate, however dystocia does. The presence of dystocia reduced second pregnancy rates by 10.67%. Using the probability of dystocia predicted from the MI's in the sample, it is found that on average, every 1 point increase in MI added 0.62% to the probability of the occurrence of second pregnancy, over the range represented by the data. Relationships among MI, dystocia and second pregnancy are nonlinear and exhibit diminishing marginal effects. These relationships indicate optimal production and profitability occur at varying maturities which are altered by animal type, economic environment, production system, and management regime. With these captured relationships any single group of heifers may be ranked by profitability given their physical characteristics, and the applicable production, management and economic conditions.
A three-year study evaluated postweaning winter grazing system management on primiparous heifers at two locations. Weaned heifers were assigned to a development system: (1) graze corn residue then winter range, (2) graze winter range, or (3) graze winter range then placed in drylot. A combination of artificial insemination (AI) and natural mating was used at time of breeding based on location. Pregnant heifers were assigned to one of three corn residue fields in late gestation based on previous heifer development. Weaned heifers developed on corn residue had similar BW and ADG during winter grazing and after breeding, compared to heifers developed on winter range. The effect of post-weaning management on reproductive performance was similar for all heifer treatments. Heifers developed on winter range or drylot had similar ADG compared to heifers developed on corn residue, during late gestation.
The challenge for sustainable organic dairy farming is identification of cows that are well adapted to forage-based production systems. Therefore, the aim of this study was to compare the grazing behaviour, physical activity and metabolic profile of two different Holstein strains kept in an organic grazing system without concentrate supplementation. Twelve Swiss (HCH ; 566 kg body weight (BW) and 12 New Zealand Holstein-Friesian (HNZ ; 530 kg BW) cows in mid-lactation were kept in a rotational grazing system. After an adaptation period, the milk yield, nutrient intake, physical activity and grazing behaviour were recorded for each cow for 7 days. On three consecutive days, blood was sampled at 07:00, 12:00 and 17:00 h from each cow by jugular vein puncture. Data were analysed using linear mixed models. No differences were found in milk yield, but milk fat (3.69 vs. 4.05%, P = 0.05) and milk protein percentage (2.92 vs. 3.20%, P < 0.01) were lower in HCH than in HNZ cows. Herbage intake did not differ between strains, but organic matter digestibility was greater (P = 0.01) in HCH compared to HNZ cows. The HCH cows spent less (P = 0.04) time ruminating (439 vs. 469 min/day) and had a lower (P = 0.02) number of ruminating boli when compared to the HNZ cows. The time spent eating and physical activity did not differ between strains. Concentrations of IGF-1 and T3 were lower (P ≤ 0.05) in HCH than HNZ cows. In conclusion, HCH cows were not able to increase dry matter intake in order to express their full genetic potential for milk production when kept in an organic grazing system without concentrate supplementation. On the other hand, HNZ cows seem to compensate for the reduced nutrient availability better than HCH cows but could not use that advantage for increased production efficiency.
Postnatal nutrition has immediate and long-lasting effects on beef heifer reproductive efficiency, longevity, and productivity. This article reviews the effects of nutrients and nutritional management on reproduction in developing heifers. In addition, the current debate on the preferred target weight for heifers at breeding is discussed.
Determining the optimal weight for breeding replacement heifers has been a goal of researchers for decades. It is an important question because replacing cows in the beef herd is expensive. Finding the answer is a complex problem because of the inter-related nature of the economic and physiological variables. Patterson et al. (1992) may have expressed the nature of the problem best when he said, “Although puberty in the female and the events that precede its onset may be fixed from a physiological standpoint, the animal and management environment in which it is placed are in constant transition.” This indicates that the optimum depends on economic, as well as the biological factors. Recent studies conducted by University of Nebraska researchers (Funston and Deutscher 2004, and Martin et al. 2007) at the West Central Research and Extension Center (WCREC) have shown the fertility rates between groups of heifers fed to different average sizes prior to breeding were not statistically different, while the feed costs for the heavier heifers was greater than that of the lighter ones. Thus, the economic analyses in these studies were based on the development cost of cattle groups. This study also suggested that optimal heifer size was less than the traditionally accepted 64 to 65 percent mature body weight (PMBW). The data collected in the above WCREC studies was used to conduct a rigorous economic analysis of optimal breeding weight using classical economic optimization theory. A profit equation was the central tool, as suggested by Fuez (1991). This profit equation consisted of five revenue equations and three cost equations, all of which were affected by the heifer’s pre-breeding size, PMBW. The complex nature of the profit equation required a numerical methodology to derive the optimal PMBW.
Programs for developing replacement heifers are designed for heifers to calve at 2 yr of age and to extend their stayability in the herd while minimizing feed cost. The experimental objective was to determine whether developing prepuberal heifers on less dietary energy and to a BW of 55% rather than 65% of mature BW at 14 mo of age would compromise ovarian development and reduce fertility. In a 3-yr study, 8-mo-old Angus (n = 60/yr) and composite MARC II (n = 60/yr) heifers were assigned equally by age, BW and breed to receive either a low (LG) or high (HG) weight-gain diet fed to achieve an ADG of either 0.45 or 0.8 kg/d from 8 to 15 mo of age, including the first 21 d of breeding, and then transferred to pasture. At 14 mo, heifers were housed with fertile bulls for 47 d. Estrus was monitored for 21 d. Within 12 h after detection of estrus, ovarian length and height, preovulatory follicle diameter, and antral follicle count (AFC) were measured by transrectal ultrasonography. Corpus luteum (CL) volume and plasma progesterone concentration were measured 5 to 15 d after estrus. Data were analyzed by ANOVA with treatment, breed, and year and their 2-way interactions as independent variables. At breeding, HG heifers were heavier than LG heifers (419.9 vs. 361.8 ± 7.5 kg; P < 0.01); ADG for the treatment period was 0.79 vs. 0.47 ± 0.04 kg/d (P < 0.01), respectively. In 2010 and 2011, 97.2% of heifers were cyclic by 21 d of breeding. Size of the ovary, preovulatory follicle, CL, and AFC did not differ between HG and LG, but preovulatory follicle diameter and ovarian length were greater (P ≤ 0.05) for MARC II vs. Angus heifers. Progesterone concentrations were less for LG vs. HG heifers (P ≤ 0.02), whereas CL volume was not affected by treatment or breed but was correlated positively with preovulatory follicle size (P < 0.01). Total AFC ranged from 5 to 49 and was correlated positively with ovarian volume but was not associated with fertility. A greater proportion of HG vs. LG heifers conceived within the first 21 d of the breeding period (64.4 vs. 49.2 ± 3.8%, respectively; P < 0.01), but overall pregnancy rate was not affected by treatment (83.0 vs. 77.7 ± 3.1%, respectively; P > 0.10). Pregnancy rate was 10% less (P < 0.01) for Angus vs. MARC II heifers. Developing beef heifers at a lesser ADG to a lighter BW (55 vs. 64% of mature BW) at breeding did not influence postweaning ovarian development, AFC, or compromise pregnancy rate during the 47-d breeding period.
Longevity of cattle is correlated to reproductive success. Many studies in different species report the influence of maternal nutrition on progeny performance, health, and reproduction. Maternal nutrient status can cause epigenetic alterations to the genome of the developing fetus, which can potentially impact future generations. This review will discuss fetal programming mechanisms as well as maternal nutritions impact on placental development and progeny heifer performance and reproduction due to nutrient restriction, age, or production status. Furthermore, we will discuss how early neonatal nutrient intake and type can influence future productivity in the beef and dairy cow. Understanding how maternal nutrient regulation stimulates fetal programming will enable livestock producers to generate replacement females better adapted to their environment. Understanding how these factors influence progeny performance is vital to the future sustainability of cattle producers by producing replacement females be...
The results of UNL's 2003 Nebraska Farm Real Estate Market Survey indicate a slight decline in overall land values compared to 2002 (-.4 percent). However, variability within the state and among land types indicates more complexity and less uniformity in changes than in previous years. In the past 16 years overall land values declined only twice (1999 and 2003). Thus, the slight decline in 2003 values is not strong evidence of a leveling off in the generally increasing trend in land values, yet large declines of land values in some areas raise concern over what economic forces are at work.
Summary This paper deals with theory, methods and problems in the analysis of categorical data in animal breed/ng when a threshold model is postulated foi an underlying normal distribu- tion of phenotypes. Linear and nonlinear statistical models potentially useful for esti- mating parameters of the underlying and out- ward distributions are reviewed and extended. Methods for evaluating the genetic value of candidates for selection from single or multiple populations are discussed comparatively.
Seventy-two mature, nonpregnant, nonlactating Hereford cows (400 kg) were utilized in a comparative slaughter trial to investigate the effects of carcass composition on the metabolizable energy (ME) required for maintenance in winter. Body condition score (CS), live weight (LW) and weight:height ratio (WTHT) were evaluated and compared as estimators of carcass composition in cows. Cows ranged in LW, CS and WTHT from 275 to 595 kg, 2.0 to 8.0 units and 2.29 to 4.62 kg/cm, respectively. Live weight, CS and WTHT predicted total carcass energy (TMCAL, r2 = .81, .85 and .83), carcass fat (FAT, r2 = .78, .82 and .80), carcass protein (PRO, r2 = .71, .74 and .70) and carcass water (WAT, r2 = .78, .71 and .77) with similar accuracy. When composition was expressed on a per unit weight basis, CS was superior to LW and WTHT as predictors of TMCAL/hot carcass weight, TMCAL/LW and FAT/hot carcass weight (r2 = .82, .60 and .64; .83, .58 and .62; and .82, .64 and .68, respectively). Forty-seven cows were individually fed a complete diet (2.50 Mcal ME/dry matter) in drylot for 114 d in yr 1 and 115 d in yr 2. Daily feed intakes were adjusted each week to maintain constant LW throughout the winter. Data were analyzed by fitting the model: ME intake = k-1 (carcass energy change) + f(CS)LW.75, where k = efficiency of ME use for carcass energy change and f(CS) = function of CS. Year as a class variable and the expression .1028 + .0234(CS) - .0025(CS)2 accounted for 41% of the variation in Mcal ME for maintenance/LW.75. Condition score was more closely related to carcass composition in mature cows than was LW or WTHT and cows in either a thin (CS = 3) condition or a fat (CS = 7) condition required less (4.4% and 8.9%) Mcal ME/LW.75 for maintenance than cows in moderate (CS = 5) condition.
The objective of this study was to determine if pregnancy rates (PR) differed between beef heifers bred to fertile bulls on either their puberal (E1, n = 89) or third (E3, n = 67) estrus. Heifers were obtained from two lactations (Manhattan, L1; and Miles City, L2), and the experiment was conducted at Miles City. Heifers were assigned randomly within location to either E1 or E3. Heifers were fed to gain .56 kg.head-1 X d-1 and observed twice daily for estrus. After exhibiting first estrus (puberty) and breeding, each heifer in E1 was palpated rectally on d 6, 9 and 12 +/- 1 d (estrus = d 0) for the presence of a corpus luteum, and a venous blood sample was collected for assay of progesterone by radioimmunoassay. Heifers in E3 were palpated and bled on the same schedule as heifers in E1 after first estrus and after being bred to a fertile bull at third estrus. Pregnancy rates were determined by rectal palpation at approximately 38 d post-breeding. Location of origin did not affect (P greater than .10) weight at puberty or weight at breeding; however, heifers from L1 were younger (P less than .05) than heifers from L2 at puberty and breeding. Pregnancy rates were 57 and 78% for heifers in E1 and E3, respectively (P less than .05). Weight at breeding did not influence (P greater than .10) pregnancy rates. The probability of heifers in E1 becoming pregnant increased (P less than .05) with increasing age, while age was not a factor (P greater than .10) for heifers in E3. These results indicated that fertility of puberal estrus in beef heifers is lower than third estrus. Higher fertility of third estrus may be related to maturational changes associated with cycling activity.
Data for gestation length, birth weight, calving difficulty (percent assisted) and survival from birth to weaning were analyzed from 4,639 calves by 290 sires of 14 Bos taurus breeds (Hereford, Angus, Jersey, South Devon, Limousin, Simmental, Charolais, Red Poll, Brown Swiss, Gelbvieh, Maine Anjou, Chianina, Pinzgauer and Tarentaise) mated to Hereford and Angus cows. The calves were produced over a 7-yr period in a germ plasm evaluation program. Variance components were estimated for breed of sire (sigma 2b), sire within breed of sire (sigma 2s) and progeny within sire (sigma 2w) random effects. Estimates of sigma 2b and sigma 2s direct genetic variance were similar for gestation length and calf survival. Estimates of sigma 2b genetic variance were greater than for sigma 2s for birth weight and calving difficulty. Estimates of total heritability [h2t = 4(sigma 2b + sigma 2s)/(4 sigma 2b + sigma 2s + sigma 2w)] and within-breed heritability (h2w = 4 sigma 2s/sigma 2s + sigma 2w) indicated that gestation length (h2t = .77, h2w = 64) and birth weight (h2t = .79, h2w = .46) are under a high degree of direct genetic control, calving difficulty (h2t = .42, h2w = .21) is under a moderate degree of direct genetic control and calf survival (h2t = .11, h2w = .07) is under a low degree of direct genetic control. Estimates of genetic correlation for between (rb) - and within-breed (rg) sources of genetic variation were comparable in direction, but tended to be stronger between than within breeds.(ABSTRACT TRUNCATED AT 250 WORDS)
Three heifer development trials were conducted with 337 crossbred heifers (125, 105 and 107 heifers in trials 1, 2 and 3, respectively) over a 3-year period. Heifers were fed low quality fescue hay ad libitum plus 0, 1.22 or 2.45 kg of ground ear corn (GEC) daily during the winter feeding phase of all three trials. Winter gains and final winter and summer condition scores increased (P less than .05) in each trial as winter level of GEC increased. In each trial, summer gains followed the reverse order of winter gains (P less than .05). Conception rate, mean number of days pregnant (as determined by rectal palpation) and adjusted weaning weight of progeny increased linearly with winter level of GEC when pooled over trials. Differences between animals fed 0 and 2.45 kg of GEC were significant. Conception rate and adjusted weaning weight of progeny of the heifers retained in the breeding herd increased (P less than .05) as level of GEC increased when data were pooled over trials. Calving date and percentage live progeny were not significantly affected by winter treatment. Summer daily gains and condition scores were increased by additional summer energy (2.45 kg GEC/day) in trial 3. Conception rate and mean number of days pregnant (conception date) favored heifers given the summer supplementary feeding (2.45 kg GEC) treatment. Among heifers retained in the breeding herd, there were no significant differences between the 0- and 2.45-kg GEC summer treatment groups in conception rate, calving date, percentage live progeny or adjusted weaning weight of progeny.
Our objective was to determine whether beef heifers could be developed by delaying the majority of weight gain until the last third of the developmental period before the onset of the breeding season. Spring-born Angus x Hereford heifers were used in each of two consecutive years and were allotted at weaning to gain either .45 kg/d for the entire developmental period (yr 1 = 159 d, n = 40; yr 2 = 168 d, n = 40; EVENGAIN) or to gain .11 kg/d from d 0 to 112, followed by .91 kg/d from d 112 to 159 (yr 1, n = 40) or d 168 (yr 2, n = 40; LATEGAIN). Body weights and condition scores were determined at d 0, 112, and 159 (yr 1) or d 0, 112, and 168 (yr 2). Heifers were subjected to a 60-d breeding season. Frame scores and pelvic areas were determined at the conclusion of the breeding season. Actual daily gains for EVENGAIN heifers for yr 1 and yr 2 were .60 and .51 kg/d, respectively. LATEGAIN heifers gained .25 and .05 kg/d during the restricted phases from d 0 to 112, followed by 1.14 and 1.32 kg/d during the accelerated growth phases for yr 1 and 2, respectively. Body weight at the onset of the breeding season and weight at puberty were not different between treatments in either year. Age at puberty did not differ in yr 1, but, age at puberty in yr 2 was delayed (P < .01) in LATEGAIN (406.9 d) compared to EVENGAIN (386.3 d) heifers. The LATEGAIN and EVENGAIN heifers had similar pelvic areas, frame scores, and body condition scores in each year. First-service conception rates of both groups were similar in yr 1 (55.5 vs 55.3%). In yr 2, LATEGAIN heifers tended (P = .18) to have an increase in first-service conception rate compared to EVENGAIN heifers (71.1 vs 56.4%). No treatment differences occurred in either average age of conception or overall pregnancy rates at the conclusion of the breeding season for either year. The LATEGAIN heifers were developed to a similar BW on 12 (P < .01) and 2.5% (not statistically significant) less feed for yr 1 and 2, respectively, compared to EVENGAIN heifers. We interpret these data to indicate that delaying the majority of weight gain until late in heifer development may decrease costs without detrimental effects on reproductive performance.
Objectives were to characterize changes in concentrations of LH, FSH, and estradiol-17beta (estradiol) in blood and populations of ovarian follicles of prepubertal cattle during waves of follicular development and to evaluate interactions between day after follicular aspiration and month prepuberty for these variables. During each month (month prepuberty), ovarian follicles of prepubertal cattle were aspirated to induce synchronous emergence of a wave of follicular development (day after follicular aspiration). Characteristics of ovarian follicular development and concentrations of hormones in blood were evaluated during the synchronous wave of follicular growth. Multiple regression was used to estimate hormonal variables and evaluate interactions for variables between day after follicular aspiration and month prepuberty. There were no interactions between day after follicular aspiration and month prepuberty for numbers of follicles </= 4 or > 5 mm or concentrations of LH, FSH, and estradiol. The pattern of change in these variables after follicular aspiration was, therefore, similar each month prepuberty. There were interactions between day after follicular aspiration and month prepuberty for frequency and amplitude of LH pulses and size of largest follicle. There were also endocrine changes that were related to follicular development after follicular aspiration throughout the peripubertal period.
The objective of this study was to determine primiparous heifer performance following three different heifer development strategies that were the result of timed nutrient limitation. Two hundred eighty-two spring-born MARC III heifers were weaned at 203+/-1 d of age and 205+/-1 kg BW. The experiment was conducted on two calf crops with 120 heifers born in 1996 and 162 heifers born in 1997. Treatments consisted of different quantities of the same diet being offered for a 205-d period. Heifers in the HIGH treatment were offered 263 kcal ME/(BWkg)0.75 daily. Heifers in the MEDIUM treatment were offered 238 kcal ME/(BWkg)0.75 daily. Heifers in the LOW-HIGH treatment were offered 157 kcal ME/(BWkg)0.75 daily the first 83 d and 277 kcal ME/(BWkg)0.75 daily for the remainder of the 205 d. Treatments differed in total ME intake (P < 0.001); heifers on the HIGH treatment consumed 3,072+/-59 Mcal/heifer, those on the MEDIUM treatment consumed 2,854+/-21 Mcal/heifer, and those on the LOW-HIGH treatment consumed 2,652+/-19 Mcal/ heifer. At the beginning of breeding, heifers on the HIGH treatment were taller at the hips (P = 0.01) and weighed more (P < 0.001) than heifers in the other two treatments. The percentage of heifers that calved expressed as a fraction of the cows exposed did not differ among treatments (89.7%; P = 0.83). The age of heifer at parturition (P = 0.74) and the time from first bull exposure to calving (P = 0.38) did not differ among treatments. Birth weight of calves (P = 0.80) and the calves' weaning weight (P = 0.60) did not differ among the treatments. Calf survival rate on the LOW-HIGH treatment (73%) was lower than that on the moderate treatment (89%; P = 0.007) but did not differ from that on the HIGH treatment (81%; P = 0.26). The second-calf pregnancy rate (92.8%) for cows with a nursing calf at the start of breeding did not differ between treatments (P = 0.83). These findings suggest that as long as heifers are growing and meet a minimal BW before mating, patterns of growth may be altered in the post-weaning period without a decrease in the ability of the heifer to conceive or a decrease in calf growth potential. However, limit-feeding heifers may decrease first-calf survival. These alterations in postweaning gain through monitoring the amount of feed offered can be used to optimize feed resources.
Prices for different classes of feeder steers and heifers, slaughter steers and heifers, slaughter cows and bulls are reported in Tables 1-23. These prices are analyzed in the text of this publication. Discounts and premiums for various weights, grades and sex are identified. Each price series is analyzed to determine long-term price trends and seasonal patterns. Feeder and live cattle basis are calculated using USDA monthly average cash prices and the monthly average futures prices, Tables 14-15, 23. Carcass cut-out values are reported in Tables 24-26.
Four yr of yearling grow/finish systems were evaluated. In the first 2 yr, treatments were (1) animals grown at a ‘fast’ rate of winter gain (0.73 kg/d; FAST) using-wet corn gluten feed as an energy source and (2) animals grown at a ‘slow’ rate of winter gain (0.20 kg/d; SLOW). Treatments were designed to evaluate compensatory gain on summer grass. Summer forage intakes were measured in an attempt to explain any compensatory growth. Steers on the SLOW treatment gained faster during summer grazing compared to FAST; however, no differences were noted for kg forage intake/head. Steers on the SLOW treatment consumed more forage, as a percentage of body weight, compared to FAST. In yr 3 and 4, additional treatments were added: steers wintered at a ‘fast’ rate of gain using corn as an energy source (CORN), steers grown at a ‘fast’ rate of gain for half of the winter, followed by a ‘slow’ rate of gain (FAST/SLOW), and steers grown at a ‘slow’ rate of gain for half of the winter followed by a ‘fast’ rate of gain (SLOW/FAST). With this treatment structure, the effect of winter energy source and duration and severity of winter growth restriction were evaluated. Steers on the FAST/SLOW, SLOW/FAST, and SLOW treatments gained faster in the summer compared to FAST and CORN. Compensation ranged from 20–40%, and was not impacted by winter energy source or duration or severity of winter growth restriction. In addition, the 4 yr of yearling systems were evaluated in relation to calf-finishing (CALF). Only FAST and SLOW treatments were used. Steers on the CALF treatment consumed less feed and converted more efficiently, but gained less with more d on feed compared to yearlings. Steers on the FAST treatment were more profitable ($/head) compared to CALF and SLOW. Based on results from the above trials, steers must be fed to gain at increased rates over the winter to lower slaughter breakeven. Only 20–30% compensation on grass is realized following winter restriction.
Sustainable cowherds require replacement of cull cows either internally via raised heifers or externally with purchased females. Managing raised replacements begins with a weaned heifer calf and continues on through her second pregnancy and calving. Replacement costs were estimated from research conducted in Nebraska for spring-calving cowherds and included the opportunity cost of the heifer calf. The analysis, based on research data, showed that heifer development programs targeted to 50 to 55% of mature BW (MBW) at first breeding can be successful, challenging the traditional target of 65% of MBW at first breeding. The lower BW programs achieved first-calf pregnancy rates near 90% of heifers exposed and resulted in development costs that were $25 to $30 per head lower than the higher BW programs. Finishing or selling open first-calf heifers was shown to be an economically viable enterprise given development costs were not too large. Numbers of open first-calf heifers were shown not to greatly affect total development costs. The primiparous heifer can increase the overall heifer development costs if not managed properly. Research showed that strategic nutritional programs for primiparous heifers resulted in successful reproduction without large increases in costs (<$2 per head). Price cycles were shown to affect the overall heifer development costs through the opportunity cost of the heifer calf and the value of calves and culled heifers and cows. Income tax treatment of purchased vs raised replacement females differs; however, the overall magnitude of differences were shown to not likely be a major determinant of whether to raise or purchase replacements.
Summary A STUDY was made of the effect of relative first calving date in beef heifers on life- time production using production records records from two beef herds. The study in- volved 2036 spring calves from 481 cows weaned in October or November of each year. An initial calving group was determined for each heifer based on the relative birth date of her first calf. A subsequent calving group was similarly assigned to each addi- tional calf from the same cow. Heifers calving initially in the Early, first and second groups tended to calve earlier throughout the remainder of their productive lives than heifers calving initially in later groups. However, repeatability estimates for calving group in the two herds were 0.092 and 0.105 indicating that only moderate improve- ment might be made by culling cows that calve late during the normal calving season. Calves born in earlier groups grew signifi- cantly faster from birth to weaning and weighed more at weaning than calves born in later groups. Lifetime production was signifi- cantly affected by initial calving group. Early calving heifers had higher average annual life- time calf production than late calving heifers. This study indicates the importance of man- aging and breeding heifers so they will calve early in the season and thus tend to maintain early calving throughout their productive lives. Such management should contribute profit in the cow-calf operation.
SUMMARY Two studies were conducted to determine effects of precalving feed level on calf birth weight, calving difficulty and subsequent fertil- ity of the dam. Pregnant dams were held in drylots and fed a low (3.2 or 3.4 kg TDN) or high (6.3 or 6.4 kg TDN) daily feed level for 90 days before calving. Rations fed in drylot immediately postcalving ranged from 7.6 to 8.6 kg TDN content. Lactating dams grazed com- mon pastures after the drylot phase and were bred by artificial insemination during a 45-day breeding season. High gestation feed levels increased calf birth weights (P
Selection and management of replacement beef heifers involve decisions that affect future productivity of an entire cowherd. The decision to breed heifers as yearlings involves careful consideration of the economics of production and the reproductive status, breed type, or genetic make-up of the heifers involved. Reproductive competence is established as a consequence of a specific program of developmental events leading to organization of functionally competent reproductive tissues and organs. The timing of puberty is critical in determining whether a heifer remains in the herd and the extent to which lifetime productivity is achieved. Because most components of fertility that influence calving and subsequent reproductive performance are not highly heritable, it is logical to assume that the majority of factors related to reproductive performance in cattle are influenced almost entirely by management. Utilization of various prebreeding management technologies enables producers to improve breeding performance of heifers during the first breeding season and during the subsequent calving and rebreeding period as 2-yr-olds. These practices help to ensure that heifers entering the herd as raised or purchased replacements will contribute to the general performance and productivity of an entire cowherd immediately, and cumulatively long-term. This review examines the relative merits of these various practices and provides an assessment of the adoption rate of specific reproductive management proce-dures for replacement beef heifers.
Management of replacement beef heifers should focus on factors that enhance physiological processes that promote puberty. Age at puberty is important as a production trait when heifers are bred to calve as 2-yr-olds and in systems that impose restricted breeding periods. Calving by 24 mo of age is necessary to obtain maximum lifetime productivity. Because the reproductive system is the last major organ system to mature, factors that influence puberty are critical. The influence of environment on the sequence of events leading to puberty in the heifer is dictated largely by the nutritional status of the animal and related effects on growth rate and development. Management strategies have been designed to ensure that heifers reach a prebreeding target weight that supports optimum reproductive performance, and consequences of inadequate or excessive development have been evaluated. Those strategies are based on evidence linking postweaning nutritional development with key reproductive events that include age at puberty and first breeding, conception, pregnancy loss, incidence and severity of dystocia, and postpartum interval to estrus. Management alternatives that ultimately affect lifetime productivity and reproductive performance of heifers begin at birth and include decisions that involve growth-promoting implants, creep-feeding, breed type and(or) species, birth date and weaning weight, social interaction, sire selection, and exogenous hormonal treatments to synchronize or induce estrus. Basic and applied future research efforts should converge to match in a realistic manner the production potential of the animal with available resources. Strategies that incorporate consideration of nutrition, genetics, and emerging management techniques will need to be tested to enable producers to make decisions that result in profit. This review evaluates the current status of knowledge relating to management of the replacement beef heifer and serves to stimulate research needed to enhance management techniques to ensure puberty at an optimal age.
Reproductive traits were evaluated in Bos taurus and Bos indicus crossbred heifers that were fed different diets during the postweaning period. The study was designed in a 2 x 2 x 2 factorial arrangement of treatments. Angus x Hereford (AH; n = 148) and Brahman x Hereford (BH; n = 148) heifers were sorted after weaning by body weight into light (LW) and heavy (HW) weight blocks. Heifers in each weight block were assigned to diets calculated to reach a target weight of 55% (LE) or 65% (HE) of their projected mature weights by the start of the breeding season. Puberty was determined after a 160-d observation period and characterized by the following criteria: 1) behavioral estrus, 2) presence of a palpable corpus luteum (d 6 to 10; estrus = d 0), and 3) rise in serum progesterone above 1 ng/ml (d 6 to 10). A higher (P = .01) proportion of AH heifers than of BH heifers reached puberty by the breeding season (93% vs 67%). Interactions of breed x weight block and energy level x weight block also contributed to this difference. Weight at puberty was heavier (P = .001) among HE than among LE heifers and greater for heifers in HW than for those in LW blocks (P = .02). Differences in prebreeding weight, body condition, average daily gain, hip height, and pelvic area were influenced selectively by breed, energy level, or weight block. Pregnancy rates were higher (P = .01) among AH than among BH heifers. Incidence and severity of dystocia was influenced by the breed x energy level interaction (P = .01). Brahman x Hereford heifers had less (P = .01) dystocia than AH heifers, HE heifers had less (P less than .02) dystocia than LE heifers, and HE-AH heifers had less (P less than .01) dystocia than LE-AH contemporaries. Subsequent duration of the postpartum interval to estrus was shorter (P = .002) among AH than among BH females. Pregnancy rates at the end of the 2nd yr were higher (P = .02) among LW than among HW females and weights were heavier (P = .001) at weaning among calves weaned from BH dams.
This paper concerns continuation ratio models for multinomial responses. These are conditional probabilities used in logit models to define the dependence of the multinomial proportions on explanatory variables and unknown parameters. A distinctive feature of these models is that if one models the various continuation ratios separately, then resulting estimates and test statistics are asymptotically independent. This allows the partitioning of likelihood ratio statistics and the search for effects in specific categories of an ordinal response variable. Models that use the same parameters for different continuation ratios are suitable for estimating more global differences. The fitting of these models to actual data is illustrated, including an example from a pharmaceutical study. The results show that different models are suitable for modelling complementary sorts of differences between multinomial response distributions.
Reproductive performance and weaning weight of the first calf was determined in 221 Brahman crossbred heifers fed to weigh either 272 (TW1) or 318 kg (TW2) at the start of their first breeding season (target weight). Heifers were divided into light- (below average) and heavyweight (above average) groups on the basis of initial weight. Within each target weight, heifers were fed in three lots. One lot contained lightweight heifers, the second contained heavy heifers and the third was composed of one-half heavy- and one-half lightweight heifers. Heifers were fed for 200 d before the start of the first breeding season. More heifers in TW2 showed estrus and became pregnant in the first 20 d of the breeding season and more were pregnant at the end of the first breeding season. These same differences in reproductive performance were also noted the second year. Each heifer exposed in TW2 weaned 43.4 kg more calf than those in TW1. An average heifer in TW2 was fed 220 kg more corn and 100 kg less hay than a corresponding heifer in TW1. Estrus and pregnancy rate for lightweight heifers in TW1 and TW2 were not improved by sorting and feeding them separately.
Numerous studies have been reported that relate to the influence of cattle type on production efficiency; however, most reported studies have been concerned with output characteristics. This review concentrates on the influence of cattle type on the input requirements and more specifically, energy requirements. Data are presented that show that energy is required for maintenance, growth, gestation and lactation and requirements for each of these functions vary among cattle types. Data are presented that suggest 70 to 75% of total annual energy requirements are required for maintenance functions and variation in requirements for maintenance appear to be greater than variation in requirements for growth, gestation or lactation. In general, variation in maintenance requirements appears to be positively associated with genetic potential for measures of production, e.g., rate of growth or milk production. Reported results suggest that animals having genetic potential for high productivity may have less advantage or be at a disadvantage in a more restrictive environment, suggesting the need for synchronization of production environment and germ plasm resources. Some of the sources of variation in maintenance requirements have been discussed. Data are cited that suggest little of the variation in maintenance energy expenditures is attributable to variation in total body composition per se. However, considerable evidence has accumulated to show that a relatively large proportion of maintenance energy expenditures can be attributed to energy expenditures of visceral organs, especially the liver and gastrointestinal tract. High rates of energy expenditures of these tissues appear to be directly or indirectly associated with the high rates of protein synthesis in these tissues. Greater use of differing research approaches and assimilation of the results are needed to develop an understanding of the reasons for variation among animals in maintenance energy expenditures or energetic efficiency.
SUMMARY The bias of several logit estimators and their corresponding variance estimators is investigated in small samples. Their use in quantal bioassay is similarly explored. The logit transformation has been suggested in the analysis of higher dimensional contingency tables, by Woolf (1954) and many others more recently, and also in estimating the parameters of the logistic function in the quantal bioassay problem (Berkson, 1944, 1953). Various modifications of the logit have been suggested by Berkson (1953), Haldane (1955), Anscombe (1956), Tukey, mentioned by Anscombe (1956), and Hitchcock (1962). Modifications of its usual variance estimator have been proposed by Haldane, Goodman (1964) and Gart (1966). More recently Goodman, in an unpublished paper, has derived several further modifications of his estimator. In this paper we present a numerical comparison of the bias of these estimators and give conditions under which one or the other may be preferred. The use of logits in the quantal bioassay problem is briefly explored with particular reference to the asymptotic results of Hitchcock regarding the bias of the estimators.