Article

Reproductive Management of Dairy Cattle Based on Synchronization of Estrous Cycles

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Abstract

High-yielding dairy cows (199) were allotted to a control group or one of two groups for synchronization of estrus. Synchronization of estrus was accomplished by either insertion of a progesterone-releasing intravaginal device (progesterone coil) for 7 days with .5 mg of the prostaglandin analogue cloprostenol (Estrumate) administered 1 day before removal of the progesterone coil, or by administration of .5 mg of Estrumate followed 13 days later by a progesterone coil inserted for 9 days. Following each estrous synchronization regimen, cows were inseminated during a fixed 6-day period (insemination week). Into one-half of the cows of each treatment group, a second progesterone coil was inserted 12 days following the fixed-time insemination for 9 days. Cows that calved within 21 days were included in a cluster and were treated and inseminated simultaneously at regular 3-wk intervals. Thus, insemination of synchronized cows was during only 6 out of each 21 days. The estrous synchronization regimens were applied so that the first fixed-time insemination for any cow occurred between 59 and 79 days after calving. Control cows were inseminated following estrus, commencing 59 days after calving. Conception rates for cows of groups 1, 2, and 3 were 50, 56, and 51%. Pregnancy rates at 25 days following the fixed-time insemination were 53, 78, and 69%, and at 100 days after calving, 57, 75, and 65%. A system of reproductive management is proposed in which observations for estrous behavior and inseminations are only during 6 days out of each 3 wk.

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... Thus, it appears that systems for controlling time of insemination or limiting amount of time for detection of estrus have been developed to the point where they are available for broad application in dairy herds (7,21,22). The economic benefits of such systems are difficult to estimate because a key consideration in this evaluation is "convenience". ...
... However, part of this reduced labor cost would be offset by additional labor to administer treatments and by cost of drugs. Perhaps the convenience of being able systematically to manage both reproduction and labor 1Folman et al. (7). PRID 7/Estrumate 6 refers to insertion of a progesterone-releasing intravaginal device (PRID) for 7 days with Estrumate given on day 6. ...
... Estrumate 13/PRID 9 refers to administration of Estrumate 13 days before insertion of a PRID for 9 days. iFolman et al. (7). PRID 7/Estrumate 6 refers to insertion of a progesterone-releasing intravaginal device (PRID) for 7 days with Estrumate given on day 6. ...
Article
Reproductive performance affects profit of dairy herds because it directly affects milk produced per cow per day, number of replacements produced, and rates of voluntary and involuntary culling. High producing cows will reproduce at a satisfactory rate if they are managed properly. There appears to be direct relationship between herd management and reproductive performance. Thus, reproductive performance and profit respond positively to improvements of rates of detection of estrus, improvements of rates of conception, and improvements of management of the periparturient cow. Pharmacological procedures are now available for controlling time of estrus and insemination in groups of cattle. It is feasible to limit the breeding period in a herd to 1 wk of each 3-wk interval. Primary benefits of controlled breeding are convenience and efficient use of labor for detection of estrus and insemination. Biotechnical procedures such as embryo transfer and insertion of specific genes may enhance rates of genetic improvement for important economic traits.
... Conception rate found improved from 66.1 in untreated to 74.6 percent following CIDR insertion from 4 to 9 days after first insemination in normal cows [19] . PRID administration on day 12 to 21 after insemination improved the conception rate slightly from 49 to 54 percent [20] . The higher conception in repeat breeder cows supplemented with progesterone post AI, might be due to improved uterine environment for embryo survival and development [21] Endometrial secretions, essential for stimulating and mediating the changes in conceptus growth and differentiation throughout early pregnancy was directed by the steroid environment generated by the ovary [22] . ...
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The high incidence of Repeat breeding is one of the most common problems faced by the farmers and veterinarians in India and it causes huge economic loss to the farmers. A total of 90 repeat breeder cows that were either brought to the Teaching Veterinary Clinical Complex, Veterinary College and Research Institute, Tirunelveli, or to the infertility camps at nearby villages of Tirunelveli formed the experimental animals for the present study. The repeat breeder cows were randomly and equally assigned to one of the three groups. viz. control (Group I; n=30) CIDR (Group II; n=30) and CIDR + post AI CIDR (Group III; n=30). The pregnancy status was checked 60 to 90 days post insemination by rectal palpation. The conception rate following controlled breeding with CIDR (group II) was (P<0.05) higher at 43.33 percent than untreated cows (Group I), with CIDR and post insemination treatment with CIDR (group III) was the highest at 63.33 percent than group I & II. Hence, Controlled breeding using CIDR and PGF2α in combination with post insemination CIDR therapy or alone could be used to improve the conception rate in repeat breeder cows under field conditions.
... Breeding clusters. The breeding cluster is one method that can be used to organize groups of cows for programmed breeding (Folman et al., 1984). For example, if the EWP is 50 d before scheduled AI, then a breeding cluster of cows can be organized to fall within a certain range of DIM to fit the targeted first breeding date. ...
Article
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Challenges limiting reproductive efficiency of high milk- producing cows include interrelationships among body condi- tion, dry matter intake, transition from the dry period to lacta- tion, onset of normal estrous cycles, detection of estrus, and embryonic survival. Attention is required to details associated with diet formulation; feed bunk management; cow comfort in free stalls, holding pen, and milking parlor during extremes of temperature and humidity; proper hoof care; milking man- agement and mastitis prevention; control of ovulation and es- trus; and early nonpregnancy diagnosis. Intensive management of transition cows should involve monitoring key metabolic markers using hand-held devices. This should allow early de- tection of illnesses that can be followed by proven interven- tions to alleviate their residual effects. Body condition should be monitored more closely to reduce dry cow and transition problems and prevent prolonged anestrus by maximizing early postpartum dry matter intakes. Cow comfort should be moni- tored more closely to minimize standing time for milking, maximize standing time for estrus and feed intake, and maxi- mize resting time for rumination and more efficient milk syn- thesis. Estrus may be detected using automated techniques such as pedometry, rump-mounted pressure-sensitive radio- telemetric devices, and in-line parlor tests for milk progester- one or estrogen. More highly fertile heifers may be impreg- nated using sexed semen, sexed embryos, or clones to provide more replacement heifers because of declining fertility of lac- tating cows. Strategies to impregnate high-producing cows will require more ovulation control before first and subsequent services without detection of estrus. Because of high rates of embryonic death, more pregnancies may be achieved by using sexed or cloned embryos. Many reproductive technologies used today, including programmed breeding, will be refined and incorporated into the management of cows on fewer dairy farms with more cows per farm. Despite trends for longer lac- tations associated with bST and lesser pregnancy rates, re- newed lactations following parturition will continue to be es-
... These findings are in agreement with those reported by Moreira et al. (2001) and with the hypothesis that fertility is improved when cows are exposed to higher concentra- Journal of Dairy Science Vol. 87, No. 4, 2004 tions of P4 during the luteal phase before AI (Fonseca et al., 1983) or before PGF 2α injection (Folman et al., 1984 ). Increased P4 concentrations in cows whose estrous cycles were presynchronized (experiment 2) also may be the consequence of reduced variation in the stage of the estrous cycle at which the Ovsynch protocol was initiated (Table 5). ...
Article
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Two experiments examined pregnancy after synchronized ovulation (Ovsynch) with or without progesterone (P4) administered via controlled internal drug release (CIDR) intravaginal inserts. In experiment 1, 262 lactating cows in one herd were in 3 treatments: Ovsynch (n = 91), Ovsynch + CIDR (n = 91), and control (n = 80). The Ovsynch protocol included injections of GnRH 7 d before and 48 h after an injection of PGF20. Timed artificial insemination (TAI; 57 to 77 d postpartum) was 16 to 20 h after the second GnRH injection. Cows in the Ovsynch + CIDR group also received a CIDR (1.9 g of P4) insert for 7 d starting at first GnRH injection. Control cows received A-I when estrus was detected using an electronic estrus detection system. Based on serum P4, 44.1% of cows were cyclic before Ovsynch. Pregnancy rates at 29 d (59.3 vs. 36.3%) and 57 d (45.1 vs. 19.8%) after TAI and embryo survival (75.9 vs. 54.5%) from 29 to 57 d were greater for Ovsynch + CIDR than for Ovsynch alone. In experiment 2, 630 cows in 2 herds received TAI at 59 to 79 d postpartum after 6 treatments. Estrous cycles were either presynchronized (2 injections of PGF2alpha 14 d apart; n = 318) or not presynchronized (n = 312). Within those groups, Ovsynch was initiated 12 d after second presynchronization PGF2alpha, and used alone (n = 318) or with CIDR inserts for 7 d (1.38 g of P4/insert, n = 124 or 1.9 g of P4/insert, n = 188). Before Ovsynch, 80% of cows were cyclic. Presynchronization increased pregnancy (46.8 vs. 37.5%) at 29 d after TAI, but CIDR inserts had no effect on pregnancy in experiment 2. Overall embryonic survival between 29 and 57 d in experiment 2 was 57.7%. Use of CIDR inserts with Ovsynch improved conception and embryo survival in experiment 1 but not in experiment 2, in part due to differing proportions of cyclic cows at the outset. Presynchronization before Ovsynch enhanced pregnancy rate.
... Using progesterone-releasing intravaginal device (PRID) prostaglandin procedure, the conception rate was reported to be higher when PRID was inserted in the early (days 1-10) rather than late (days 11-20) stage of the oestrous cycle (Folman et al. 1984). In a more recent study , reproductive performance was evaluated according to whether cows showed high or low plasma progesterone concentration, at the onset of PRID prostaglandin treatment. ...
Article
This report reviews the most recent developments in prostaglandin-based oestrous synchronization programmes for postpartum dairy cows and addresses the efficiency of controlled breeding protocols based on such developments for cows with abnormal ovarian conditions. A double prostaglandin protocol applied 11-14 days apart seems to be capable of bringing most cows to oestrus. Because of varying oestrus onset times, improved conception rates are obtained following artificial insemination (AI) at detected oestrus rather than fixed-time AI in prostaglandin-treated cows. The administration of oestradiol or human chorionic gonadotrophin, or both these hormones, after prostaglandin treatment, improves the synchrony of oestrus yet does not enhance the conception rate. Progesterone-based treatments for oestrous synchronization are considered the most appropriate for non-cyclic or anoestrous postpartum dairy cows; prostaglandin alone being ineffective because of the absence of a mature corpus luteum in these cows. Improved oestrus synchrony and fertility rate have been reported using short-term progesterone treatment regimes (7-9 days) with or without oestradiol benzoate combined with the use of a luteolytic agent given 1 day before, or at the time of, progesterone withdrawal. The ovulation synchronization (Ovsynch) protocol, based on the use of gonadotrophin releasing hormone and prostaglandin, was developed to coordinate follicular recruitment, CL regression and the time of ovulation. This protocol allows fixed time insemination and has proved effective in improving reproductive management in postpartum dairy cows. However, timed AI following Ovsynch seems to have no beneficial effects in heifers, because of an inconsistent follicle wave pattern, and in anoestrous cows, given their lack of prostaglandin responsive CL. To date, there are several prostaglandin based, fixed-time insemination oestrous synchronization protocols for use in early postpartum dairy cows with ovarian disorders such as ovarian cysts and acyclicity.
... Subsequent to d -10, more diestrous cows (HLH and LLH) were exposed to elevated progesterone during 7 d before PGF 2α was injected, whereas fewer numbers of late diestrous (LHH and HHH) and follicular phase (HHL) cows were exposed to elevated progesterone during the remaining 7 d before PGF 2α was injected (Figure 3). These results are consistent with the hypothesis that fertility is greater when cows are exposed to higher concentrations of progesterone during the luteal phase before AI (Fonseca et al., 1983) or before injection of PGF 2α (Folman et al., 1984). These greater pregnancy rates may be related to the fact that the dominant follicle continues to grow until it matures and ovulates or, in the presence of progesterone produced by the CL, it turns over and is replaced by a fresh dominant follicle containing an oocyte of normal fertility (Adams et al., 1992; Smith and Stevenson, 1995). ...
Article
Full-text available
In experiment 1, 705 cows were assigned to three treatments: 1) the Ovsynch protocol (a GnRH injection given 7 d before and another 48 h after one PGF2alpha injection); 2) PGF2alpha + Ovsynch (one PGF2alpha injection given 12 d (d -22) before initiating Ovsynch (d -10); and 3) 2xPG12 (two PGF2alpha injections 12 d apart; d -15 and -3, followed 48 h later by a GnRH injection. All cows were inseminated (d 0) 16 to 20 h after the GnRH injection on d -1. Cyclic status was estimated by serum progesterone. More cows were in early diestrus at d -10 for PGF2alpha + Ovsynch (36%) and 2 x PG12 (29%) versus Ovsynch (19%). Multiparous cows receiving PGF2alpha + Ovsynch had greater pregnancy rates via ultrasonography at d 28 after AI (42%) than contemporaries after Ovsynch (28%) or 2xPG12 (27%) but did not differ significantly at palpation 10 to 30 d later (28, 19, and 17%, respectively). Pregnancy of first-parity cows was similar across treatments at 28 d (41%) or at palpation (33%). Pregnancy rates for 128 anestrous cows were lower, regardless of treatment. Overall embryo survival from d 28 until palpation was 72% but was only 44% in 2xPG12 cows that were anestrus through d -10. Experiment 2 included the three treatments above plus controls (one GnRH injection 7 d before PGF2alpha and AI after estrus). Preovulatory follicles were 6 to 11% larger near estrus in controls than on d -1 in cows receiving GnRH. More controls ovulated by 32 h after onset of estrus than were treated cows by 32 h after GnRH, but percentages (79 to 94%) were similar by 40 h. In multiparous cows, PGF2alpha before Ovsynch increased pregnancy rates, whereas the 2xPG12 protocol produced similar pregnancy rates as Ovsynch across parities. Ovulation was effectively induced by 40 h after GnRH.
... Over the past 25 yr, researchers (8,11) have developed reproductive management protocols that synchronize the time of estrus using PGF 2a. Synchronization with PGF 2a was successful when cows were bred to a detected estrus, because estrus detection rates increased and management of AI was more efficient than daily detection of estrus (24). ...
Article
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Lactating dairy cows have poor reproductive efficiency because of low fertility and low rates of estrus detection. To eliminate the dependence on detection of estrus, we have recently developed a timed artificial insemination (AI) protocol that synchronized the time of ovulation using GnRH and PGF2 alpha. The effectiveness of this protocol as a management tool was compared with standard reproductive management. Lactating dairy cows (n = 333) from three herds were randomly assigned at parturition to two groups. Control cows were managed according to the typical reproductive strategy of the farm that relied on detection of estrus, the a.m.-p.m. breeding rule, and periodic use of PGF2 alpha. Treated cows had timed AI after synchronization of ovulation with GnRH and PGF2 alpha. For both groups, the voluntary waiting period was 50 d postpartum. Pregnancy diagnosis was performed by ultrasound between 32 and 38 d post-AI. Nonpregnant cows were inseminated again using the original treatment until diagnosed as pregnant or until culled from the herd. Median days to first AI (54 vs. 83) and days open (99 vs. 118) were lower for treated cows than for control cows, respectively. Pregnancy rates for the first AI were similar (37% vs. 39%) for the two groups even though treated cows were bred at an earlier time postpartum. More treated cows than control cows were pregnant at 60 d (37% vs. 5%) and at 100 d (53% vs. 35%) after calving. Thus, this protocol allowed effective management of AI in lactating dairy cows without the need for estrus detection.
... They could become more common in pastoral-based seasonal systems if the first form of failure is inherited to some extent, even if in association with NEB. Systems of controlled breeding may need to be considered so that oestrous events can be predicted before first and subsequent inseminations, so that extended inter-service intervals are avoided and delays in breeding and re-breeding are minimised (Folman et at 1984;Macmillan 1985). ...
Article
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Lactation has been negatively associated with fertility because pregnancy rates in maiden heifers exceed those obtained after first or subsequent calvings. The extent of this difference is less in pasture-fed dairy cows (<10%) than in American Holsteins (>20%) fed grain and conserved forages. The latter cows have pregnancy rates to first insemination and oestrus detection rates of only 40 to 45%. This suggests that the subsequent fertility of inherently fertile Holstein heifers may be severely compromised by high levels of milk production. International comparisons show that pasture-fed dairy cows may experience extended periods of anovulatory anoestrum but have normal fertility (60% pregnancy rate to first insemination) once cycling. The high-producing American Holstein may ovulate within 4 weeks postpartum but is more likely to continue ovulating without being detected in oestrus.
... Commercial dairy farms are challenged with making the most profitable management decisions among many options and implementing them correctly. Methods for enhancing fertility and breeding efficiency include detection of estrus (ED) (Xu et al., 1998;Rorie et al., 2002), synchronization of estrus (Folman et al., 1984;Momcilovic et al., 1998), and synchronization of ovulation and timed AI (TAI) (Pursley et al., 1995;Moreira et al., 2001;Souza et al., 2008). The newest TAI programs for first AI (i.e., Double-Ovsynch and G6G) not only increase the AI service rate but also increase conception rate or pregnancy per AI (P/AI) to TAI (Carvalho et al., 2018). ...
Article
Although hormonal synchronization programs can improve reproductive efficiency of dairy herds, some farmers question the economics of these programs based on the upfront cost of hormonal treatments as opposed to the economic value of the resulting reproductive performance. Our aim was to compare the economic impact of reproductive management programs that incorporate varying degrees of detection of estrus and timed artificial insemination (AI) in dairy herds with year-round calving in confinement total mixed ration systems. A reproductive economic analysis simulation model was used to compare the economic impact of pairs of reproductive management programs. We simulated sets of scenarios for 2 analyses. In the first analysis, we calculated the economic impact of switching from a Presynch-Ovsynch program to a Double-Ovsynch program that included a second PGF2α treatment during the Breeding-Ovsynch portion of the program (Double-Ovsynch+PGF). In the second analysis, we conducted a break-even analysis in which the cost of hormonal treatments was incrementally increased within various reproductive management programs. Our analyses revealed that a Double-Ovsynch+PGF program, the most intensive program evaluated, was more profitable than other programs compared, including a Presynch-Ovsynch program with 100% timed AI or a Presynch-Ovsynch program that incorporated detection of estrus, despite the higher upfront cost incurred by using more hormonal treatments. This advantage remained until the cost of hormones was increased 5 to 14 times current US market prices and 2 to 6 times current European market prices. The cost of GnRH had a greater impact on net profit gain than the cost of PGF2α. In conclusion, more intensive reproductive programs that use more hormonal treatments but result in substantially increased reproductive performance are more profitable than less intensive programs and remain so even if hormone prices are unusually high.
... These findings are in agreement with those reported by Moreira et al. (2001) and with the hypothesis that fertility is improved when cows are exposed to higher concentra-Journal of Dairy Science Vol. 87, No. 4, 2004 tions of P4 during the luteal phase before AI (Fonseca et al., 1983) or before PGF 2α injection (Folman et al., 1984). Increased P4 concentrations in cows whose estrous cycles were presynchronized (experiment 2) also may be the consequence of reduced variation in the stage of the estrous cycle at which the Ovsynch protocol was initiated (Table 5). ...
Article
Postpartum anestrus is one of the major limitations to achieving acceptable pregnancy rates. The Ovsynch protocol is an excellent tool to improve reproductive efficiency of dairy cows because it can induce estrous cycles in anestrous cows. In the first experiment, administering two PGF2" injections to lactating dairy cows 14 days apart with the second injection given 12 days before the Ovsynch protocol increased (P<0.05) pregnancy rate by 10 percentage points in cycling and noncycling cows. Inserting a progesterone-releasing insert (CIDR) for 7 days during the Ovsynch protocol did not further increase pregnancy rates. In a second experiment, a resynchronization treatment consisting of a used CIDR inserted for 7 days from days 13 to 20 after insemination increased (P<0.05) embryo survival from day 30 to 58 by 11 percentage points but failed to increase overall rate of return to estrus and conception rate at the second AI (first eligible estrus after first AI).
... Recent advances in the understanding of reproductive physiology of lactating dairy cows has led to the development of numerous management strategies and technologies aimed to improve overall reproductive efficiency of dairy herds (Thatcher et al., 2006). Estrous detection aids (Xu et al., 1998;Rorie et al., 2002), hormonal synchronization of estrus (Folman et al., 1984;Momcilovic et al., 1998), timed artificial insemination (TAI; Pursley et al., 1995;Moreira et al., 2001;Souza et al., 2008), and computerized record systems (Losinger and Heinrichs, 1996) are among the technologies most commonly used by modern dairy farms to improve breeding efficiency and fertility (Caraviello et al., 2006). Unfortunately, under most circumstances, it is difficult to determine whether the on-farm application of these new reproductive management programs and technologies will translate into actual economic benefits to the farm. ...
Article
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Because the reproductive performance of lactating dairy cows influences the profitability of dairy operations, predicting the future reproductive and economic performance of dairy herds through decision support systems would be valuable to dairy producers and consultants. In this study, we present a highly adaptable tool created based on a mathematical model combining Markov chain simulation with partial budgeting to obtain the net present value (NPV; $/cow per year) of different reproductive management programs. The growing complexity of reproductive programs used by dairy farms demands that new decision support systems precisely reflect the events that occur on the farm. Therefore, the model requires productive, reproductive, and economic input data used for simulation of farm conditions to account for all factors related to reproductive management that increase costs and generate revenue. The economic performance of 3 different reproductive programs can be simultaneously compared with the current model. A program utilizing 100% visual estrous detection (ED) for artificial insemination (AI) is used as a baseline for comparison with 2 other programs that may include 100% timed AI (TAI) as well as any combination of TAI and ED. A case study is presented in which the model was used to compare 3 different reproductive management strategies (100% ED baseline compared with two 100% TAI options) using data from a commercial farm in Wisconsin. Sensitivity analysis was then used to assess the effect of varying specific reproductive parameters on the NPV. Under the simulated conditions of the case study, the model indicated that the two 100% TAI programs were superior to the 100% ED program and, of the 100% TAI programs, the one with the higher conception rate (CR) for resynchronized AI services was economically superior despite having higher costs and a longer interbreeding interval. A 4% increase in CR for resynchronized AI was sufficient for the inferior 100% TAI to outperform the superior program. Adding ED to the 100% TAI programs was only beneficial for the program with the lower CR. The improvement in service rate required for the 100% ED program to have the same NPV as the superior 100% TAI program was 12%. The decision support system developed in this study is a valuable tool that may be used to assist dairy producers and industry consultants in selecting the best farm-specific reproductive management strategy.
... Pregnancy rates were higher (P = 0.02) in the present study when synchronization protocols were started during diestrus (57.0%) versus all other stages of the estrous cycle (34.8%). Similarly, in a previous study (Moreira et al., 2000), pregnancy rates were highest (75%) when the initial GnRH treatment was given on d 10 of the estrous cycle, coinciding with the approximate time of emergence of the second follicular wave in cattle (Ginther et al., 1989), or perhaps due to exposure to higher concentrations of P4 before PGF 2α treatment (Folman et al., 1984). However, that study (Moreira et al., 2000) involved a small number (n = 24) of heifers, and the pregnancy rate (75%) was based on only 4 heifers. ...
Article
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The objective was to compare pregnancy rates in nulliparous Holstein heifers given PGF(2alpha) 24 h before, or concurrent with, removal of an intravaginal progesterone-releasing (CIDR) insert in 3 timed artificial insemination (TAI) protocols. Heifers (from 2 herds) were assigned randomly, over 11 mo, to 1 of 3 modified Ovsynch protocols. On d 0 (without reference to the stage of the estrous cycle), all heifers were given 100 microg of GnRH i.m. and a CIDR insert (containing 1.9 g of progesterone). In the PG-7/P4-8 protocol (n = 99), PGF(2alpha) was given on d 7, and CIDR inserts were removed on d 8. In the PG-7/P4-7 (n = 98) and PG-8/P4-8 (n = 102) protocols, PGF(2alpha) administration and CIDR removal occurred concurrently, on d 7 or 8, respectively. In all 3 protocols, a second GnRH treatment (100 microg) was given 48 h after PGF(2alpha) with TAI 16 to 20 h later. Blood samples were collected (subset of 124 heifers) on d 0, 7, 10 or 11 (i.e., at TAI), and 17. Pregnancy rates (32 d after TAI) for protocols PG-7/P4-8, PG-7/P4-7, and PG-8/P4-8 were 61.8, 55.6, and 54.1%, respectively. Pregnancy rate was higher when synchronization was initiated during diestrus than when initiated at other stages (57.0 versus 34.8%). Although pregnancy rates were not affected by season, there was an interaction between protocol and season; pregnancy rates were significantly lower in summer in heifers subjected to PG-7/P4-7 and PG-8/P4-8, but season did not affect pregnancy rates in heifers subjected to PG-7/P4-8. In summary, giving PGF(2alpha) 24 h before CIDR removal, followed by TAI (PG-7/P4-8 protocol), resulted in consistent pregnancy rates, regardless of season, relative to protocols involving PGF(2alpha) treatment concurrent with CIDR removal.
... Furthermore, studies have reported that high progesterone concentrations prior to insemination have a positive effect on the development of ovulatory follicles [14,18]. High levels of fertility have also been demonstrated in animals affected by high concentrations of progesterone prior to the PGF 2α injection [8]. Similarly, the present study demonstrated that the administration of a single dose of PGF 2α to animals with high plasma progesterone levels before the initiation of the Cosynch protocol increased pregnancy rates. ...
Article
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The objective of this study was to evaluate pregnancy rates to timed artificial insemination (TAI) following presynchronization with a single dose of PGF2α ten days before CoSynch-56 protocol in Brown Swiss crossbred cows and heifers. Group I (GI) cows (n=89) and heifers (n=39) received PGF2α ten days prior to Cosynch-56 protocol while Group II (GII) cows (n=82) and heifers (n=38) received CoSynch-56 protocol only. Pregnancy was evaluated using ultrasonography 30-35 days after TAI. Pregnancy rates did not differ significantly between GI and GII (34.4% and 28.3 %, respectively, P>0.05). However, pregnancy rates differed significantly (P<0.05) between cows and heifers in GII (34.1% and 15.7%, respectively). Furthermore, pregnancy rates of heifers in GI was significantly higher than that of heifer in GII (P<0.01, 41.0% and 15.7%, respectively). Notably, pregnancy was not achieved in GII heifers with plasma P4 values < 1ng/ml. In conclusion, presynchronization with PGF2α before Cosynch-56 protocol did not enhance pregnancy rates in Brown Swiss cows but did in heifers. Also, high P4 levels may enhance overall pregnancy rates of cows and heifers subjected to the Cosynch-56 protocol.
... Grouping Cows for Reproductive Management. Once progestin products for synchronizing estrus became available, the concept of grouping or clustering cows (i.e., weekly or biweekly) according to calving dates for group management was introduced (Britt et al., 1972;Folman et al., 1984). The scheme utilized in the former report for dairy cows ( Figure 3) used MGA to synchronize first inseminations and the next potential insemination, whereas in the latter report a progesterone-impregnated intravaginal insert and PGF 2α analog were used. ...
Article
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Basic knowledge of mechanisms controlling reproductive processes in mammals was limited in the early 20th century. Discoveries of physiologic processes and mechanisms made early in the last century laid the foundation to develop technologies and programs used today to manage and control reproduction in dairy cattle. Beyond advances made in understanding of gonadotropic support and control of ovarian and uterine functions in basic reproductive biology, advancements made in artificial insemination (AI) and genetics facilitated rapid genetic progress of economically important traits in dairy cattle. Technologies associated with management have each contributed to the evolution of reproductive management, including (1) hormones to induce estrus and ovulation to facilitate AI programs; (2) pregnancy diagnosis via ultrasonography or by measuring conceptus-derived pregnancy-associated glycoproteins; (3) estrus-detection aids first devised for monitoring only physical activity but that now also quantitate feeding, resting, and rumination times, and ear temperature; (4) sex-sorted semen; (5) computers and computerized record software packages; (6) handheld devices for tracking cow location and retrieving cow records; and (7) genomics for increasing genetic progress of reproductive and other economically important traits. Because of genetic progress in milk yield and component traits, the dairy population in the United States has been stable since the mid 1990s, with approximately 9 to 9.5 million cows. Therefore, many of these technologies and changes in management have been developed in the face of increasing herd size (4-fold since 1990), and changes from pastoral or dry-lot dairies to increased housing of cows in confinement buildings with freestalls and feed-line lockups. Management of groups of “like” cows has become equally important as management of the one. Management teams, including owner-managers, herdsmen, AI representatives, milkers, and numerous consultants dealing with health, feeding, and facilities, became essential to develop working protocols, monitor training and day-to-day chores, and evaluate current trends and revenues. Good management teams inspect and follow through with what is routinely expected of workers. As herd size will undoubtedly increase in the future, practical reproductive management must evolve to adapt to the new technologies that may find more herds being milked robotically and applying technologies not yet conceived or introduced.
... PRID / prostaglandina. Ha sido validado un régimen de tratamiento que limitaba periodos de observación e inseminación a 6 días cada 3 semanas(Folman et al., 1984). Las vacas recibieron ya sea (1) un PRID por 7 días (días 1-7) con una inyección de prostaglandina al día 6, o (2) prostaglandina y 13 días después un PRID por 9 días. ...
... The 3 variables accounting for more than 78% of variation in pregnancy risk were ovulation after GnRH-2, progesterone concentration 48 h after PGF 2α , and progesterone concentration before PGF 2α .The first 2 variables are consistent with findings of many studies that indicate that cows whose ovulation is synchronized (complete luteolysis and ovulation after GnRH-2) have the greatest pregnancy risk (see Bisinotto et al., 2014). Furthermore, greater progesterone concentrations before PGF 2α improved pregnancy risk in cows inseminated at estrus compared with other treatments that did not produce as great of progesterone concentrations before PGF 2α (Folman et al., 1984). ...
Article
The objective of this study was to determine the relative importance and contribution of several physiological factors as predictors of pregnancy risk in an Ovsynch (GnRH-1 – 7 d – PGF2α – 56 h – GnRH-2 – 16 h – artificial insemination) timed artificial insemination program: (1) age of the corpus luteum (CL; original CL, new CL, or both in response to GnRH-1) and resulting progesterone concentrations as they affected luteolysis, ovulation after GnRH-2, and pregnancy risk; (2) progesterone concentration before GnRH-1 and GnRH-2 on subsequent ovulatory response to GnRH-1 and GnRH-2 as well as pregnancy risk; and (3) a combination of these factors in a multivariable logistic regression model to predict pregnancy risk. Original data from 7 published studies were combined including ovulatory responses to both GnRH injections, blood progesterone concentrations before GnRH-1, before PGF2α, and at 48 h after PGF2α, pregnancy per artificial insemination at d 32 and 60 after artificial insemination, and intervening pregnancy loss. Ovulation outcomes were greater at lesser progesterone concentrations after both GnRH injections despite the fact that pregnancy outcomes were greatest when progesterone exceeded 3 ng/mL before GnRH-1 and PGF2α, suggesting that greater progesterone concentration before GnRH-1 and incidence of ovulation act via different mechanisms to improve subsequent fertility. Ovulation after GnRH-2 and subsequent pregnancy outcome were positively related to lesser concentrations of progesterone at 48 h after PGF2α; however, for maximal pregnancy outcome, progesterone should be <0.5 ng/mL. Cows with a CL that also formed a new CL after GnRH-1 had the greatest pregnancy outcome, whereas cows with only a new CL (i.e., anovulatory cows and those at or near estrus without a CL at GnRH-1) had the poorest pregnancy outcome. Pregnancy loss was not affected by CL status during the timed artificial insemination program. Receiver operator curves produced cut points of progesterone concentration that predicted ovulation and pregnancy risk. Selected cut points of progesterone concentration 48 h after PGF2α produced true positive risks greater than 90% and false positive risks less than 25%, thus demonstrating the high predictability of ovulation after GnRH-2 and subsequent pregnancy outcome based on progesterone concentration. We conclude that progesterone concentration is highly predictive of ovulation and pregnancy risk in addition to body condition, size of ovulatory follicle, and parity.
... The breeding cluster is one method that can be used to organize groups of cows for programmed breeding (Folman et al., 1984). For example, if the EWP is 50 d before scheduled AI, then a breeding cluster of cows can be organized to fall within a certain range of days in milk to fit the targeted first breeding date. ...
... Folman et al. (19) employed treatments of progesterone and a luteolytic agent to arrange cows into 21-d postpartum inseminating groups. Such a synchronization program allowed estrous detection and AI during a 6-d period out of each 3-wk interval. ...
Article
The effect of a GnRH agonist (10 ug Buserelin) on conception rate was determined when injected into dairy cows 12 to 14 days after Artificial Insemination (AI). The following factors were taken into account: previous treatment prior to AI with Prostaglandin F2 alpha, clinical history recorded prior to AI since last calving, parity and milk yield. A number of 118 cows, from one large dairy herd, were involved in this study. A total of 210 AI's were performed, followed by 140 GnRH treatments and 70 saline injections. Reproductive events were then recorded. The rank of AI was equally distributed among the two groups. 153 AI's were preceded by a Prostaglandin F2 alpha (Dinoprost - 25 mg) treatment among which 103 were subsequently GnRH-treated and 50 were controls. Plasma progesterone concentrations were determined daily for 34 days after AI in 13 treated and 13 control cows. An Early Pregnoncy Diagnosis (EPD) from milk progesterone concentration was performed on Day 21 after AI in all cases.
Article
The purpose of this study was to describe biological outcomes of two reproductive management strategies in commercial dairy cows: estrus detection with and without the use of prostaglandin-F2alpha. At regular preinsemination examinations, cows were allocated randomly to two cohorts: 1) prostaglandin cohort -- cows with palpable corpora lutea were injected with 25 mg dinoprost tromethamine and were bred by appointment 72 and 96 hours later, followed one week later by standard estrus detection practices (twice daily observation and tail chalking, with breeding approximately 12 to 24 hours later); and 2) estrus detection cohort -- cows identified as exhibiting estrus (observed estrus) were bred through the above standard procedures, without exposure to prostaglandin therapy. Age, milk production, weight, milk progesterone levels and reproductive data were collected for all cows. Although certain between-cohort effects were statistically significant, no differences could be found between the cohorts regarding standard measures of reproductive performance (average days in milk at conception (P=0.79), services per conception (P=0.48), proportion of animals failing to conceive to artificial insemination (P=0.53), and survival analysis on time to conception (P=0.30). With evidence for biological equivalence between the two reproductive strategies, nonbiological standards such as economics or ease of execution would be appropriate in choosing between the two strategies.
Article
The ability to synchronise onset of oestrus, and hence the time of breeding and calving, offers potential economic and management benefits to dairy farmers, especially in herds with seasonally concentrated calving patterns. A trial involving 2681 cows in 11 seasonal herds was conducted to evaluate the reproductive performance of lactating dairy cows following oestrus synchronisation with a combination of progesterone, oestradiol and prostaglandin. Cows were randomly assigned within herds to synchronised and control groups, balanced for age, date of calving, body condition and breed. Cows in the synchronised group were treated with an intravaginal progesterone-releasing device containing 1.9 g of progesterone and a gelatin capsule containing 10 mg of oestradiol benzoate 10 days prior to the planned start of the breeding season (Day 0). The device was removed 8 days later on Day -2 and a luteolytic dose of prostaglandin F2alpha was administered 2 days prior to removal of the progesterone-releasing device. Returns to service for cows in the synchronised group were synchronised by inserting a previously used intravaginal device during Days 16-21 after the start of the breeding season. Cows in the control group were left untreated. The percentage of cows being inseminated during the first 5 days was 89.0% for the synchronised group compared to 29.7% for the control group. Compared to cows in the control group, those in the synchronised group had a lower conception rate to the first insemination (52.9% v. 64.3%, p<0.001), a lower conception rate to the second insemination (51.8% v. 62.5%, p<0.001), a higher percentage of empty cows at the end of the breeding season (7.3% v. 5.1%, p<0.05), and more insemination services per pregnancy to artificial insemination (2.0 v. 1.6, p<0.001). There was no difference between the synchronised and control groups in the percentage of cows pregnant to artificial insemination (81.8% v. 85.5%, p>0.10). The mean day of conception from the start of the breeding season was advanced (p>0.0 1) by 1.3 days in synchronised cows (19.9 +/- 0.7 days; mean +/- SEM) compared to control cows (21.2 +/- 0.5 days). It is concluded that the oestrus synchronisation regime used in the present study caused a reduction in fertility, which reduced the potential gains from using such a programme to increase reproductive efficiency in dairy cows.
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The objective of these experiments was to determine the effect on fertility of GnRH when used in conjunction with one or two injections of PGF2alpha. In Experiment 1, GnRH was administered 7 d before the second of two injections of PGF2alpha (14 d apart). The control group received two injections of PGF2alpha without GnRH. Conception was reduced from 63.5% for 74 controls to 48.7% for the 79 heifers and cows that had been treated with GnRH, but estrus detection and pregnancy rates were similar. In Experiment 2, 85 heifers and cows received GnRH at a random stage of the estrous cycle, followed in 7 d by PGF2alpha. Thirty to 32 h after PGF2alpha, a second dose of GnRH was given to induce ovulation of the preovulatory follicle, followed by one fixed-time insemination 18 to 19 h later (treatment designated as GnRH, PGF2alpha, and GnRH). Controls (n = 85) were given PGF2alpha and inseminated at estrus. Although conception rate was not different, one fixed-time insemination after the GnRH, PGF2alpha, and GnRH treatment tended (35.3%) to reduce fertility compared with effects of the control (47.1%). It is unclear how an injection of GnRH during the intervening week between two injections of PGF2alpha reduced fertility in Experiment 1. However, in Experiment 2, when GnRH was given 7 d before one injection of PGF2alpha and when ovulation was induced with a second GnRH injection, one fixed-time insemination seemed to produce acceptable fertility in dairy cows but probably less than that when inseminations were based on detected estrus.
Article
Israeli-Holstein breed dairy heifers (n=571), 13 to 15 mo old, were utilized in two experiments. In Experiment 1, the reproductive performance of synchronized heifers was compared with that of untreated controls. The heifers in both groups were inseminated following the detection of estrus. In Experiment 2, all heifers were synchronized and inseminated following the detection of estrus. Half of the animals in this experiment also received one or two fixed-time inseminations 72 and 96 h after the last synchronization treatment. Synchronization of estrous cycles was performed by two prostaglandin F2alpha (PG) injections given 12 d apart. In the control group of Experiment 1, observation of estrous behavior and insemination of heifers detected in estrus were carried out daily throughout the experiment. In the synchronized groups of Experiments 1 and in 2, the management of reproduction consisted of estrus detection followed by the insemination of heifers in estrus carried out only during 6 d of every 3 wk. Five days following the second PG injection, 86% of the heifers were detected in estrus, 71% of them at 49 to 96 h after treatment. In Experiment 1, age at first insemination, age at conception, and conception rate were, respectively, 425 d, 446 d and 54% in the control group vs 432 d (P<0.02), 449 d and 62% in the PG-treated group. In Experiment 2, the respective figures were 436 d, 462 d and 59% in the group inseminated following the detection of estrus vs 427 d (P<0.002), 464 d and 51% (P<0.05) in the group in which heifers were inseminated at estrus and also received one or two fixed-time inseminations.
Article
Two experiments examined effects of GnRH administered within 3 h after onset of estrus (OE) on ovulation and conception in dairy cows. In experiment 1, 46 cows received either saline, 250 microg of GnRH, or 10 microg of the GnRH analogue, Buserelin. Cows were observed for estrus, blood samples were collected, and ovulations were monitored by ultrasound. In controls, 76% of cows had intervals from estrus to ovulation of < or = 30 h and 24% had intervals > 30 h. Treatment with either GnRH or GnRH analogue (data combined) increased magnitude of LH surges and decreased intervals from estrus to LH surge or to ovulation. Treated cows all ovulated < or = 30 h after OE. Among control cows, plasma estradiol concentrations before estrus correlated positively with amplitudes of LH surges. Higher plasma progesterone was observed in the subsequent estrous cycle in GnRH-treated cows compared to control cows with delayed ovulations. Experiment 2 included 152 primiparous and 211 multiparous cows in summer and winter. Injection of GnRH analogue at OE increased conception rates (CR) from 41.3 to 55.5% across seasons. In summer, GnRH treatment increased CR from 35.1 to 51.6%. Across seasons, GnRH increased CR from 36.0 to 61.5% in cows with lower body condition at insemination and GnRH increased CR (63.2 vs. 42.2%) in primiparous cows compared to controls. Use of GnRH eliminated differences in CR for cows inseminated early or late relative to OE and increased CR in cows having postpartum reproductive disorders. In conclusion, GnRH at onset of estrus increased LH surges, prevented delayed ovulation, and may increase subsequent progesterone concentrations. Treatments with GnRH increased conception in primiparous cows, during summer, and in cows with lower body condition.
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The objective was to compare the reproductive performances of Brown Swiss cows and heifers synchronized for estrus and ovulation using prostaglandin F 2 alpha (PGF2α) alone or with gonadotropin-releasing hormone (GnRH). Primiparous and multiparous cows (45 to 75 days postpartum; n = 26) and nulliparous heifers (16 to 20 months; n = 26) were randomly assigned to 2 treatment programs. GnRH injection was followed in 7 days by PGF 2α injection and then by another GnRH injection 9 days later. Artificial insemination (AI) was performed 16 h after the second GnRH injection. Injections of PGF2α were given 11 days apart AI was only carried out after estrus was detected following the first and second PGF 2α injections or, timed AI in the absence of detected estrus was carried out 72 h after the second PGF2α injection. The conception rate in first insemination, pregnancy rate and the interval from PGF2α to estrus were not different between the 2 groups. However, the estrus detection rate was greater for the group II cows (61.5%) than for the group I cows (15.4%) (P < 0.05). Pregnancy rates tended to be higher in group I cows. The GnRH-PGF2α-GnRH method allowed effective management of AI in cows and heifers without the need for estrus detection.
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In the veterinary area the utilization of the vagina as a route for drug delivery has focused on the systemic delivery of hormonal steroids to control synchrony, ovulation and fertility in a variety of livestock. There are several reasons for administering drugs to modify the menstrual cycle in humans and the estrous cycle in animals and this paper provides a comparison of the objectives of drug intervention to control reproduction in humans and livestock. In addition, the types of hormones and their concentrations found during the menstrual cycle in humans and during the estrous cycle in animals are compared. The paper also reviews the intravaginal drug delivery systems developed for the control of the estrous cycle in livestock and both conceptual and commercially available intravaginal drug delivery systems that have been described in the literature are described. The history of some of the delivery systems is included and the future directions of this area of research are discussed.
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In Experiment 1, 308 Holstein cows were assigned randomly to four treatments: 1) GnRH injection followed in 7 d by PGF2 alpha injection, then another GnRH injection 33 h later, and artificial insemination (AI) 16 to 18 h after the second GnRH injection; 2) GnRH injection followed in 7 d by PGF2 alpha injection and AI only after detected estrus; 3) injections of PGF2 alpha 14 d apart, GnRH injection 33 h after the second PGF2 alpha injection, and AI 16 to 18 h later; and 4) injections of PGF2 alpha 14 d apart, AI only after detected estrus following the second PGF2 alpha injection or, in the absence of detected estrus, at 80 h after the second PGF2 alpha injection. In Experiment 2, 227 Holstein cows were assigned randomly to two treatments: 1) GnRH injection followed in 7 d by PGF2 alpha injection, then another GnRH injection 48 h later, and AI 16 to 18 h after the second GnRH injection; and 2) GnRH injection followed in 7 d by PGF2 alpha injection and AI only after detected estrus. Although conception rates in both experiments resulting from AI made after detected estrus either tended to be greater or were consistently greater than those following GnRH injection and one fixed-time AI, pregnancy rates were of greater magnitude after fixed-time AI because of poor expression or detection of estrus.
Article
This paper describes the estrus cycles of a number of livestock breeds and reviews the controlled-release drug delivery systems that are currently available for the purpose of controlled breeding. The bovine estrus cycle is reviewed in detail, and the estrus cycles of other species are described in a manner that highlights similarities and differences between species. Pertinent formulation and pharmacokinetic information about current drug delivery systems is presented and discussed, and recent advances in this area are also described.
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This paper reviews the physiological, endocrinological and pharmaceutical literature pertaining to the design, development and optimisation of subcutaneous and intravaginal progestogen-containing drug delivery systems used in the control of synchrony and ovulation in cattle.
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The objective of this study was to evaluate the reproductive performance of lactating cows in seasonal dairy herds after estrus synchronization with PGF2alpha (PG) with or without supplementation with progesterone (P4). In Trial 1, synchronized cows (S1; n = 521) were compared with untreated control cows (C; n = 518) in 5 herds. Estrus of cows in the S1 group was synchronized with 2 treatments of PG (Lutalyse) 13 d apart. The breeding season started 2 d after the second PG. Cows were first bred by AI for 7 wk and then herd sires were used. Compared with C cows, estrus synchronization in the treated cows reduced the conception rate to first AI (61.1 vs 70.5%; P < 0.01) and the intervals from start of the breeding season to conception for cows conceiving to AI (11.0 vs 14.6 d; P < 0.05) or to both AI and natural mating (16.5 vs 18.4 d; P < 0.05). There was no effect on conception rate to second AI (68.8%), on pregnancy rate by Day 24 (72.3%) or Day 49 (86.3%) of the breeding season, or on the percentage of cows not pregnant at end of the breeding season (5.0%). In Trial 2, effects of P4 supplementation before the second PG on reproductive performance were evaluated in 4 herds. Estrus of each cyclic cow was synchronized with PG as in Trial 1. Half of the cows in each herd were treated with an intravaginal P4 device (CIDR) for 5 d before the second PG (S2+P4, n = 608), whereas the remaining half received no CIDR treatment (S2, n = 593). Compared with S2 cows, P4 treatment increased the estrous response rate to the second PG (89.6 vs 82.9%; P < 0.01), the conception rate to first AI (65.1 vs 59.7%; P = 0.07), the pregnancy rate by Day 6 of the breeding season (59.3 vs 49.0%; P < 0.001), and reduced the intervals from start of the breeding season to conception for cows conceiving to AI (8.6 vs 10.4 d; P < 0.10) or to both AI and natural mating (12.7 vs 16.4 d; P < 0.01). Treatment with a used CIDR from Days 16 to 21 after start of breeding to re-synchronize returns to service had no effect on conception rate to first or second AI but may decrease the conception rate to second AI in cows previously treated with CIDR. In conclusion, estrus synchronization with the double PG system can reduce fertility, while P4 supplementation for 5 d before the second PG can improve estrous response and overall reproductive performance. Stage of the estrous cycle at the time of the second PG can affect fertility following synchronization.
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We tested the efficacy of monitoring progesterone in dairy cows using a commercially available milk progesterone test as a determinant for administration of PGF2 alpha to induce estrus in cows before first AI. Holstein cows milked twice daily were assigned randomly for AI at their first estrus after d 42 postpartum (control) or to receive PGF2 alpha after a milk progesterone test. Milk progesterone was assessed in samples from the Monday morning milking in both groups of cows, but only those in the treatment received PGF2 alpha when milk progesterone tested high. Blood was collected before injection of PGF2 alpha on Monday afternoon to verify retrospectively the accuracy of the milk progesterone test. Agreement of serum concentrations of progesterone was 87% for high milk progesterone tests and 63% for low tests. Use of milk progesterone plus PGF2 alpha reduced days to first AI, calving intervals, rate of reproductive culling, and cost per pregnancy and increased the proportion of cows inseminated within 21 d of the beginning of breeding. As a management tool in an AI program, PGF2 alpha use is warranted and cost effective. However, the milk progesterone test is not justifiable unless the cost is significantly lower than the cost of a weekly injection of PGF2 alpha.
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Physiological stressors of high milk production and intensive management systems affect fertility and pregnancy rates (PR) in lactating dairy cows. A field study was conducted on dairy farms in the Fraser Valley of British Columbia to benchmark current reproductive performance and issues that impact local dairy farms. The results indicated a substantial reduction in reproductive performance due to inaccurate estrus detection, fertilization/ovulation failure, and embryonic mortality. Ovsynch timed artificial insemination (TAI) protocol is used for the induction and synchronization of ovulation in cattle, reducing the need for estrus detection. However, PR to Ovsynch TAI are still low. Strategies to modify Ovsynch TAI protocol were investigated in this study to increase PR. In the first experiment, Ovsynch was compared with a presynchronization treatment, using PGF2a before Ovsynch TAI to improve synchronization rates, and to a treatment of GnRH given 6 d after Ovsynch TAI, to reduce embryonic loss. Although no differences in PR were observed between treatments, days in milk in cows and age and weight in heifers affected PR. In the second experiment, the effects of pLH or hCG vs. GnRH in an Ovsynch TAI protocol were compared. Progesterone concentrations in pregnant cows were greater in the hCG group on days 7, 11, and 14, and greater in the pLH group on day 11 after breeding than GnRH group. There were no differences in synchronization rates or PR between treatments. High protein diets have been associated with reduced PR. Therefore, in the third experiment, cows either continued on a typical high protein diet, which was fed from calving, or switched to a lower protein diet, beginning 7 d before Ovsynch TAI and continued until pregnancy diagnosis. First and second lactation cows fed the low protein diet tended to have greater PR than cows fed the high protein diet. There were no differences in synchronization rates and progesterone concentrations between diets. Cows fed the lower protein diet had lower milk urea nitrogen and lower average daily milk production during treatment. Costs associated with treatments, labour, and producer compliance should be considered before recommending ovulation synchronization Ovsynch TAI protocol to dairy producers.
Article
The ocstrous cycles of 480 dairy cows were synchronized with prostaglandin F2α and progesterone coils during two consecutive years. Within 20 h of oestrus detection, cows were treated with saline, 100 or 250 μg GnRH, or 10 μg of the GnRH analogue Buserelin.When GnRH was administered before the spontaneous preovulatory LH surge, the height of the LH surge was 25.8 ± 2.1 ng ml−1 compared to 9.7 ± 0.7 ng ml−1 when GnRH was administered after the spontaneous surge and compared to 12.0 ± 0.8 ng ml−1 in saline-treated cows (P < 0.001). During experimental periods when first-insemination conception rates of control primiparous and multiparous cows were 30.0% and 33.3%, respectively, GnRH administered within 3 h of oestrus detection increased conception to 64.3% in primiparous cows (P < 0.005) and 56.1% in multiparous cows (P < 0.05). When GnRH was administered 16–20 h after oestrus detection or during experimental periods when conception of control animals was higher than 50%, treatment with GnRH had no effect on conception. Multiparous cows which required two to four inseminations and were treated with GnRH within 3 h of oestrus detection had a conception rate of 28.6% when inseminated within 3 h of oestrus detection compared to 67.9% when inseminated 4–30 h following oestrus detection (P < 0.05). Primiparous cows had a significantly higher conception rate than multiparous cows among GnRH-treated animals (65.1% vs. 50.4%) but not among control animals (53.0% vs. 46.2%).
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Reproductive efficiencies were compared among herds with (treated, n = 25) or without (visited control, n = 25) routine synchronization of estrus and herds without investigator visits (unvisited control, n = 22). Treatment groups were subdivided based on participation in veterinary herd health programs. Reproductive tracts were palpated rectally at 21-d intervals for 6 mo in two sets of treated and visited control herds. Data were collected during the visitation period and from the 6-mo period before visits. In treated herds, cows more than 40 d postpartum with a corpus luteum received prostaglandin F2 alpha. In visited control herds, cows received prostaglandin F2 alpha after 82 d postpartum if they were not observed in estrus. Routine synchronization of estrus did not enhance herd reproductive efficiency compared with no synchronization of estrus in visited herds. Small changes in reproductive efficiency occurred during visits in herds with an established reproductive health program. However, herds not using a health program had 15.2 fewer d from calving to insemination, and the pregnancy rate at 120 d postpartum was 13.0 percentage units higher than before herd visits. Consequently, reproductive performance of those herds during visits was similar to that of contemporaries under a herd health program.
Article
Dairy cows (n = 571) were treated with 1) one or two injections of prostaglandin F2 alpha given 11 or 14 d apart, 2) two injections given 14 d apart and a progesterone coil inserted 8 d after the first injection for a 7-d period; or 3) a coil inserted for 7 d and prostaglandin injected 1 d before its removal. Cows given two prostaglandin injections that conceived had higher progesterone concentrations during the luteal phase preceding AI than did cows that did not conceive. Cows with progesterone coils that conceived did not have higher progesterone concentrations than did cows that did not conceive. Older cows had lower progesterone concentrations than younger ones, and they appeared in estrus earlier after treatment. In four daily observations, 75% of cows were seen in estrus within 7 d after treatment. Cows mounting two or more times had a conception rate (62%) similar to that of cows that stood to mount. Fewer cows (56%) treated with prostaglandin that had low concentrations of progesterone appeared in estrus than did cows with high progesterone (84%). Cows treated with prostaglandin differ from cows treated with progesterone coils in respect to manifestation of estrus and to the relationship between plasma progesterone and conception.
Article
Three experiments with 571 dairy cows indicated that significantly more primiparous cows given two prostaglandin F2 alpha injections 14 d apart conceived within 30 d of first AI than did cows given two injections 11 d apart (84 vs. 62%). Fewer multiparous cows given two injections 14 d apart and inseminated after estrus conceived than did cows given two injections and a progesterone intravaginal coil inserted 8 d after the first injection (42 vs. 66%). Fewer cows given one injection of prostaglandin and inseminated at estrus conceived than did cows given two injections 14 d apart and a progesterone coil (39 vs. 66%). Conception rates of cows given two prostaglandin injections were positively related to plasma progesterone concentrations 2 and 4 d before the second injection (r = .81 and .86). Cows with progesterone concentrations below 5 ng/ml, 2 d before the second prostaglandin injection, and synchronized by two prostaglandin injections or by two injections and a progesterone coil had conception rates of 36 and 63%, respectively. Cows with progesterone concentrations above 5 ng/ml had a conception rate of 75 and 46% in the two treatments, respectively. Conception after estrus synchronization depends on the method and on the plasma concentrations of progesterone. Progesterone coils may be used before AI to enhance fertility in cows with low progesterone concentrations.
Article
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Our objective was to determine whether pregnancy rates following first services would be improved by supplementing lactating dairy cows with exogenous progesterone via a progesterone-releasing intravaginal device. Estrus was induced in cows with PGF2 alpha (3-wk clusters of cows ranging from 42 to 63 d postpartum) following a positive milk test for high progesterone. Cows were inseminated at estrus (d 0), and progesterone was administered via the device from d 5 to 13 or d 13 to 21 following estrus; untreated inseminated cows served as controls. Blood was collected from each cow on d 5, 13, and 21 to determine concentrations of progesterone in blood serum. A fourth group of inseminated cows not receiving PGF2 alpha served as an additional untreated, and nonbled, control group. Pregnancy rates at first services, which were followed by insertion of the device, were unaffected by treatments. Concentrations of progesterone in serum were higher in pregnant than nonpregnant cows on d 13 but similar in cows regardless of postinsemination treatment. By d 21, when concentrations of progesterone remained consistently higher as a result of pregnancy, cows given progesterone from d 13 to 21 had higher progesterone in their blood serum, regardless of pregnancy status, than cows receiving progesterone from d 5 to 13. Only serum progesterone in nonpregnant controls on d 21 was less than that of nonpregnant cows given progesterone on d 13 to 21. Pregnancy rates of cows returning to estrus 21 to 27 d after their first service tended to be higher (60 versus 39%) in those cows previously treated with exogenous progesterone than in controls. Furthermore, the proportion returning to estrus 17 to 27 d after first service was reduced in cows previously supplemented with exogenous progesterone (27 versus 49%). Days from calving to conception were 19 d fewer in cows previously treated with progesterone than controls, because average intervals to first service were decreased by 13 d relative to controls. We conclude that supplementing cows with progesterone after insemination initially failed to improve pregnancy rates but appeared to increase pregnancy rate at the subsequent service.
Article
L'interdiction des oestrogènes par l'Union Européenne en octobre 2006 a obligé les laboratoires commercialisant des traitements de maîtrise des cycles à chercher rapidement des alternatives à leur utilisation. Le laboratoire CEVA Santé Animale a ainsi modifié son protocole PRID® en ajoutant une administration de prostaglandine F2 alpha et en raccourcissant la durée du traitement progestérone à 7 jours. Les résultats de fertilité ne sont pas différents de ceux obtenus avec le protocole de référence. L'objectif de cette étude était de comparer la fertilité à l'oestrus induit après un traitement progestérone de synchronisation des chaleurs de 7 jours ou de 9 jours (PRID® spirale vaginale contenant 1,55 g de progestérone; injection de prostaglandine F2a 24 heures avant le retrait; injection d'eCG le jour du retrait; IA 56 heures après le retrait). Les travaux ont porté sur 768 vaches allaitantes et 498 vaches laitières Prim' Holstein. Chez les vaches allaitantes après un traitement de 9 jours, le taux de gestation a été significativement augmenté comparativement à un traitement de 7 jours, respectivement de 70 versus 63 %. Différents facteurs individuels, la cyclicité et la phase du cycle au moment de l'instauration du traitement, le rang de vêlage, le mois d'insémination et le délai postpartum ont eu un effet significatif sur le taux de gestation à l'oestrus induit. Chez les vaches laitières, la durée de traitement n a pas eu d influence sur le taux de gestation, 52 % versus 50 %, respectivement pour une durée de traitement de 9 vs 7 jours. Ces résultats ont été influencés par le rang de vêlage.
Article
The extent of the increases in milk production resulting from improvements in the system for artificial insemination were not forecasted. But more improvements will come! For example, improvements in diagnosing sex of embryos will increase the adoption of preselection of sex as a part of embryo transfer. Later, the best 1% of cows may be inseminated with Y-sperm to create the next generation of sires, the next best 50% may be inseminated with X-sperm to create herd replacements, and the bottom 50% may be inseminated with Y-sperm to create males for beef. Bulls may be treated during embryonic development to increase their reproductive performance in artificial insemination centers and improved systems for sperm preservation will decrease numbers of sperm required for acceptable fertility. Improved tests of semen quality based upon new physicochemical principles will provide better predictors of fertility and sperm may be frozen in “sustained release” capsules to prolong effective fertility after insemination. In females, methods are evolving to induce and synchronize estrus in cattle during postpartum anestrus and during the first 5 d of the estrous cycle when no functional corpora lutea exist. Technology is also emerging to enhance the ability to detect cattle in estrus and to diagnose quickly on the farm nonpregnancy as early as 19 to 20 d after insemination. Collectively, these kinds of advances will allow systems for insemination of groups of cattle at prescribed periods with normal fertility. Advances in uses of ovarian and hypothalamic hormones will increase the numbers of oocytes from superovulation and improve their viability. Genes for simply inherited traits from other species will be inserted into the bovine genome and integrated systems for preservation of embryos will increase their viability after freezing. Collectively, the economic impact of these kinds of advances in reproductive management may rival that from artificial insemination.
Article
The purpose of this study was to define the biological efficiency of a standard estrus detection regimen, both with and without use of prostaglandin-F2α, under commercial dairy conditions.At regular pre-breeding examinations, cows were allocated randomly to two cohorts: (1) prostaglandin (PT) — cows with palpable corpora lutea were injected with 25 mg dinoprost tromethamine and bred 72 and 96 h later; and (2) heat detection (HD) — cows identified as being “in heat” through twice daily observation with tail chalking were bred ∼ 12 h later. Age, body weight, milk production and reproductive data were collected for all cows, as were milk samples for progesterone analysis.Prostaglandin use significantly affected the sensitivity of the estrus detection test, lowering it by half (0.26 vs. 0.53), plus it increased the proportion of false negatives by 61% (0.34 vs. 0.21) over controls. Consequently, the predictive value of a positive test in the PT cohort was lowered by 14% (0.79 vs. 0.90) compared with control animals. Over both cohorts, the standard estrus detection test displayed a low sensitivity and a high specificity, characteristic of a diagnostic test, but not of a screening test. The findings from this dairy suggest that current recommended estrus detection procedures may be inappropriate for their declared purpose of being screening tests for estrus and that routine prostaglandin use may exacerbate the problem.
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Two experiments were performed in two different herds to determine if utilizing prostaglandin F2α to induce estrus for first services would be effective in reducing the duration and variability of calving intervals. In Experiment 1, cows were assigned randomly as controls (n = 217) to be inseminated as they were detected in estrus (beginning d 42 to 53 postpartum depending on replicate) or treated with prostaglandin F2α (n = 185). In Experiment 2, the same treatments were utilized, except control cows (n = 124) were inseminated at their first detected estrus after d 40 postpartum, and treated cows received either one injection of prostaglandin F2α between d 54 and 63 (n = 116) or were given progesterone (via a progesterone-releasing intravaginal device) for 7 d, with the device removed 24 h after prostaglandin F2α (n = 116). More cows were inseminated and pregnancy rates were higher within 5 d after treatment with prostaglandin F2α and interval from prostaglandin F2α to first service was reduced compared with that of control cows. Duration and variation of calving intervals were unaffected in either experiment, despite the fact the elective waiting period was 6 to 23 d longer for treated cows than for controls. Prebreeding treatment with progesterone failed to improve conception rates, but the efficiency of estrous expression increased from 54% in prostaglandin F2α-treated cows to 71% in those cows also receiving prebreeding progesterone. We conclude that prostaglandin F2α was ineffective in improving reproductive performance of these herds undergood herd management. However, prostaglandin F2α offers the convenience of inseminating small groups of cows, controlling when breedings occur during the work week, and prolonging the elective waiting period without extending the calving interval.
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Lactating ovariectomized Holstein cows were treated with new (NC; 1.9 g progesterone, P4; n = 4) or used (UC; used 9 days; n = 4) controlled internal drug release (CIDR) devices for 9 days. After a 3 day clearance, CIDR types were reversed for a second 9 day period. Blood was collected twice daily for Days −1.5 to +5 and then once daily until Day +11. Milk samples and milk yield data were collected twice daily for Days −1.5 to +11.5. Intensive blood sampling (every 10 min for 8 h) was performed on Days −2, +2, +5 and +9 of Period 1. Plasma P4 (PP4), milk P4 (MP4) and luteinizing hormone (LH) were analyzed by validated radioimmunoassays. During CIDR exposure, PP4 (2.4 ± 0.14 > 1.5 ± 0.14 ng ml−1) and MP4 (7.0 ± 0.37 > 5.2 ± 0.37ng ml−1) were higher with a new CIDR (P < 0.001). Maximum PP4 (ng ml−1 ± SE(range))during CIDR exposure occurred on Day +2 and averaged 3.4 ± 0.23 (2.8–4.4) for NC and 1.9 ± 0.15 (1.4–2.6) for UC. Maximum MP4 for NC occurred on Day +2 und averaged 8.8 ± 0.98 (5.2–14.2), and for UC occurred on Day +4 and averaged 6.7 ± 0.62 (5.1–9.7). Minimum PP4 (ng ml−1 ± SE (range)) during CIDR exposure occurred on Day +8 for both treatments and averaged 1.7 ± 0.24 (1.1–3.2) for NC and 1.1 ± 0.07 (0.9–1.4) for UC. Minimum MP4 occurred on Day +9 for both treatments and averaged 5.0 ± 0.83 (2.8–10.0) for NC and 3.4 ± 0.35 (2.0–4.7) for UC. Intraclass correlations of PP4 and MP4 for cows were high (> 0.6), implying inherent differences among cows in P4 metabolism. Luteinizing hormone pulse frequency (1 ± 0.1 pulse h−1), LH mean (1.78 ± 0.20 ng ml−1), baseline (0.98 ± 0.10 ng ml−1), and pulse amplitude (2.78 ± 0.48 ng ml−1) did not differ between CIDR type or among days. Device removal during LH sampling on Day +9 increased (P < 0.09) LH baseline within an hour (0.73 ± 0.26 ng ml−1 vs. 1.30 ± 0.16 ng ml−1; before vs. after device removal). New CIDR increased PP4 and MP4 more than UC, but neither affected the dynamics of plasma LH secretion in ovariectomized cows.
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New intravaginal (CIDR) devices have been developed for the controlled administration of progesterone to livestock. A series of trials associated with the evaluation of the CIDR-B device for use in cattle showed that the amount of hormone released during a 15 day treatment period was highly repeatable and depended on initial progesterone content. In spite of this predictable hormone loss, individual treated animals showed wide variations in plasma progesterone concentrations. The effect which supplemental progesterone had on the inter-oestrous interval depended on the stage of the cycle at insertion, the duration of treatment and interactions with other compounds administered at device insertion (oestradiol benzoate) or removal (prostaglandin F2α). There were significant differences in the distribution of post-treatment intervals to oestrus among synchrony treatments, and among herds within a treatment. Synchrony was more precise with insertion periods of 14 days or more, but pregnancy rates were reduced. The results highlight the desirability of producing treatment regimes which are of short duration (10 days or less) and which combine synchronised luteolysis with synchronised ovarian follicle wave patterns.
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The professional application of agents to the manipulation of fertility of cows requires basic and applied knowledge of the physiologic mechanisms that are affected and of the pharmacologic agents that are used. In all areas of the pharmacologic manipulation of fertility, the achievement is less than the ideal, and further research is required to improve the efficiency of treatments. The induction of estrus in acyclic animals can involve a reduction in the depth of anestrus, pretreatment with progestagen to ensure estrous behavior and the formation of a normal corpus luteum, and then treatment with exogenous gonadotropin. Responsiveness to treatment can be variable and reflects the depth of anestrus of the animals. Improved treatment regimens require a knowledge of the basic mechanisms involved with the depth of anestrus, a means of assessing the depth of anestrus, and an understanding of the hormonal requirements of ovarian follicles for development and maturation in animals at different depths of anestrus. The optimal precision in the synchronization of estrus (and ovulation) in cyclic animals requires the synchronization of both follicular waves and the end of progestational phase. The end of progestational phase can be synchronized effectively using prostaglandin F2a (or analogs), or by treatment with progestagens with or without luteolytic agents. Procedures to synchronize follicular waves need to be established. The induction of superovulation can be achieved readily using gonadotropins prior to estrus synchronization using prostaglandin F2a. The responses to standard treatments in terms of ovulation rates and yield of transferable embryos are highly variable. The development of procedures to reduce this variability requires an understanding of the intra-ovarian mechanisms involved in recruitment of follicles for a wave of follicular growth, in the selection of dominant follicles for further development, and in the mechanisms controlling follicular atresia. Cystic ovarian disease can be treated effectively using HCG or GnRH (follicular cysts) or prostaglandin F2a (luteal cysts). The basic mechanisms resulting in failure of estrogen positive feedback on LH secretion (that results in cystic follicles) remain to be determined. Small but significant increases in pregnancy rates can be achieved treating cows with prostaglandin during the post-partum period, with prostaglandin to induce estrus for insemination, with GnRH or HCG at estrus, and with GnRH or progestagen treatment during diestrus. Beneficial effects of treatment have been shown in some trials but not in others.(ABSTRACT TRUNCATED AT 400 WORDS)
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Multiple regression equations were derived from data for 6,351 Holsteins for first lactations and 17,978 later lactations. Within herds each day open between 40 and 140 days of lactation resulted in an average of 4.5 kg less annual milk during current lactations of first-calf heifers and 8.6 kg less for cows in later lactations.
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To synchronize oestrus, a single dose of 0.5 mg of the prostaglandin F2α analogue cloprosterol (Estrumate) was administered to 200 post-partum beef and dairy cows. Six, 9 or 13 days following the injection of Estrumate a progesterone-releasing intravaginal device (PRID) was inserted for 12 to 16 days. Among the synchronization treatments investigated, the most promising one was to administer 0.5 mg of Estrumate followed 13 days later by a PRID inserted for 12 days. Following the use of this treatment 87% of post-partum suckling beef and dairy cows manifested oestrus within the first 3 days after PRID removal; 80% appeared in heat between approximately 36 and 72 h following PRID removal. Conception rates for untreated controls, cows inseminated once at 55 h, and cows inseminated twice at 48 and 72 h following PRID removal, were 52, 50 and 48% respectively.
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A computerized mathematical model was used to test the economic effect of changing calving intervals under typical high-yielding (63701 per 305 days for mature cows) herd conditions at 1976 prices. The effect of month of first calving was also tested in a herd where four lactations are assumed to follow at equal calving intervals. Under the prescribed conditions, cows should calve at 320-day to 360-day intervals (with two exceptions) to maximize the annual margins over concentrates, but the month of the initial calving affects the absolute level of margins over concentrates markedly (maximum £382·10 for 365-day interval for November calving, minimum £318·10 for April). This means that complete knowledge of the main input-output factors is required before recommendations can be made for an individual cow. The change in margin over concentrates for each day's delay in conception varies widely, with rates of loss as high as £1·80 per day's delay occurring.
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The effect of season on milk yield, milk composition, oestrus manifestation, oestrus cycle characteristics and conception rate was studied in high-yielding Israeli-Friesian cows. ‘Summer’ cows were allotted to control (SC) and forced ventilation (SV) groups. ‘Winter’ cows (W) were kept in one group. During July-September mean rectal temperatures at 16.00 h in primiparous and multiparous cows were 39·6 and 39·8°C, respectively in cows of the SC group, and 39·4 and 39·3°C, respectively in cows of the SV group. Mean rectal temperatures at 16.00 h of the animals in the W group during December-March were 38·9°C in both primiparous and multiparous cows. The mean 122-d milk yields in primiparous cows were 3508, 3251 and 3571 kg/cow in the SC, SV and W groups respectively (not significant (NS)). In the multiparous cows the respective yields were 4183, 4416 and 4538 kg/cow ( P < 0·05). Differences in milk composition were small and statistically NS. Observations on oestrus manifestation, performed 4 times daily, indicated that standing oestrus lasted 9·2 and 10·6 h in primiparous and multiparous cows respectively ( P < 0·05); differences between groups were statistically not significant. Oestrous cycle lengths of primiparous and multiparous cows were 21·1 and 22·5 d respectively ( P < 0·05) between ovulations and 23·0 and 28·05 d respectively ( P < 0·01) between standing heats. Cows were inseminated following standing heat only. Conception rates (on all services within experimental periods) in primiparous cows were 50, 35 and 72% in the SC, SV and W groups respectively (NS). In the multiparous cows, the respective rates were 22, 52 and 80% ( P < 0·05). It is concluded that in the present experiment hyperthermy decreased milk production to a very small extent, in spite of very high milk yields, but fertility was severely affected. It is also suggested that primiparous cows are less affected by heat stress than multiparous cows.
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The effects of days-open on milk yields in current lactations and in following lactations were estimated from 71 911 current and 68 693 following lactation records. Yields were expressed as 305-day, total and annual records, where annual record = 365 × (total yield/days between calvings). The data were grouped according to current days-open, corrected for initial yield differences and analysed separately for heifers and cows in Moshav (moderate-yielding) and Kibbutz (high-yielding) herds. Current 305-day records increased by 15 to 18 kg milk/day-open up to 90 days-open, and 2 to 3 kg/day-open thereafter. In contrast, the effects of increasing days-open on annual yields were generally small and negative, being positive only for heifers up to 90 days-open. Thus 305-day records heavily under-rated annual yields of fertile cows. For current lactations, 70 to 100 days-open for heifers and 30 to 50 days-open for cows resulted in the highest annual production. Yields in following lactations were positively associated with days-open in the previous lactation. The effect was highest in high-yielding herds, suggesting that high-yielding cows respond positively to some rest between calvings. Combining the effects of days-open on current and following lactation yields and on the calf crop: in high-yielding herds heifers had the highest productivity when mated not earlier than 70 days post partum , while in moderately-yielding herds days-open did not affect productivity. Cows in high-yielding herds achieved highest productivity at 41 to 90 days-open, while cows in moderately-yielding herds were most productive when mated as early as possible. A comparison of the economic value of sire fertility and sire transmitting ability for milk production showed that fertility may often be over-rated.
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Over a period of 1 year, three consecutive groups, each consisting of 12 postpartum Holstein cows aged from 3 to 9 years, were observed continually for 80 days. Animals were housed in a windowless free stall environment under husbandry and nutrition practices similar to those employed in commercial dairy units. A time lapse videorecorder, and two low light intensity television cameras were used to monitor behavioural activities of the cows. The stall was continuously illuminated with an intensity of 32 lux at the eye level of a standing cow. Each day the entire videotape was viewed and the number of mounts, the feeding, drinking, resting and walking activities of each cow were recorded.
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Progesterone concentrations in peripheral plasma of 18 primiparous and 34 multiparous dairy cows were determined by radioimmunoassay every 4 days, from 10 days post partum until the next conception. The interval from parturition to the first progesterone peak (greater than 4 ng/ml plasma) was significantly longer (P less than 4 ng/ml plasma) was significantly longer (P less than 0.01) in primiparous than in multiparous cows. The progesterone concentrations on Days 4-15 of the oestrous cycle were significantly lower (P less than 0.025) during the summer than in cycles occurring in winter. The conception rate during the summer was lower than in winter. In cows inseminated in summer, conception was related to the shape of the progesterone curve in the cycle preceding insemination.
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Data from 10 herds on a herd reproductive status program supported estimates of lost reproductive days per cow per year due to conception failure and missed heat as 23 and 10 days. The corresponding estimates from Ohio Dairy Herd Improvement were 14.7 and 40.3 days. The correlation within the 10 herds between days lost due to failure to conceive and total days open was .38 and between days lost due to missed heats and total days open .92.
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Two infections each of 500 mug Cloprostenol (ICI-80,996), a synthetic analogue of PGF-2alpha, 11 or 12 days apart or pretreatment for 7 days with progesterone from an intravaginal silastic coil and one injection of 500 mug Cloprostenol were both effective in synchronizing oestrus in heifers or nursing beef cows. After two inseminations at 72 and 96 hr after the end of treatment, the calving rate for cows observed in oestrus after both treatments or for cows that had oestrous-like mucus after the progesterone+Cloprostenol treatment did not differ from that of control cows, but was significantly (P less than 0-025) lower for cows diagnosed as ready for insemination by the characteristics of mucus after the two injections of Cloprostenol. Treated cows disgnosed per rectum as having inactive ovaries had a significantly (P less than 0-005) lower calving rate than those diagnosed as having active ovaries at the start of treatment. Significantly (P less than 0-005) more treated than control cows were inseminated and became pregnant in the first 15 days of the treatment period, but the overall level of reproductive efficiency was low.
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Two experiments studied the effectiveness of medroxyprogesterone acetate (MAP) and melengestrol acetate (MGA) for control of estrus in normal and anestrous dairy cows. A third experiment investigated the use of MGA for controlling estrus during 17 successive 3-week breeding periods. In Experiment 1, 73 anestrous cows received MAP (180 mg/day) or a placebo for 10 days. Conception rate for first service, total conception rate, and services per conception were 59, 88,’ 1.7 and 54, 74, 1.8 for MAP and control groups. In Experiment 2, 232 cows in four herds were classified normal or anestrous according to estrous detection during the first 7 weeks postpartum. Beginning on Day 48 postpartum, some cows received MGA (1 mg/day) for 10 days while others served as controls. The mean interval from calving to first service, average days open for cows conceiving, and services per conception were 76, 107, 2.4; 76, 123, 2.5; 74, 98, 1.9 and 75, 107, 2.0 for MGA-normal, MGA-anestrous, control-normal and control-anestrous groups. Conception rates for first service were between 50 and 53% for normal cows and between 35 and 39% for anestrous cows irrespective of hormone treatment.