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The efficiency of utilization of metabolizable energy for milk production: A comparison of Holstein with F1 Montbeliarde × Holstein cows
Abstract
The objectives were to demonstrate the potential of heat production measurements to characterize the gross and net efficiencies of dairy cows under commercial conditions and to compare the efficiencies of purebred Holstein and Montbeliarde × Holstein F1 dairy cows. The heat productions of seven Holstein (H) and seven Montbeliarde × Holstein (MH) cows were measured over two 10-day periods separated by a 75-day interval, during the summer of 2004, in a commercial high-yielding dairy herd in Israel. Energy expenditure was measured by monitoring heart rates and oxygen consumption per heart beat. Milk yield and composition were recorded for these cows and their investment of energy in the milk was calculated from the milk yield and composition. Live weight and body condition score were also recorded in parallel with these measurements. Metabolizable energy (ME) intake was estimated as the sum of heat production, energy in milk and body energy balance. The MH cows were heavier by 90 kg, had higher body condition scores by 0·9 units and secreted proportionately 0·19 and 0·38 less energy in their milk than H cows in the first and second periods, respectively. The gross energy efficiencies, expressed as the percentage of milk production plus body retention in ME intake were 48·3 and 43·4% in the first period and 45·6 and 32·8% in the second period, for H and MH cows, respectively. The milk production of MH cows in this study was lower than the potential of this cross, however, MH cows that expressed this potential would still be expected to require proportionately 0·10 greater intake of ME than H cows, per unit of energy in milk.
... The HR was recorded with a Polar instrument (Polar Electro Oy, Kempele, Finland), a model T51H HR transmitter, and a watch model S610 data logger and receiver (details in Aharoni et al., 2006). The devices were attached to the thorax behind the forelegs by means of a specifically designed elastic belt (Pegasus, Eli-ad, Israel). ...
... This increase in RE was not followed by any significant increase in the HP of the cooled cows, which was maintained at a constant level of 130.4 to 130.8 MJ/cow per day. Similar constant levels of total HP in the range of 122.6 to 135.6 MJ/cow per day were also measured in previous studies with lactating non-cooled Holstein cows, held under various feeding regimes, climate conditions and over different stages of lactation (Aharoni et al., 2005 and2006;Miron et al., 2007, unpublished). The finding of this study and of the previous ones that shower cooling and various feeding regimes hardly affect the HP of mid-lactation Holstein cows deserves further investigation. ...
... Total HP is actually the sum of HPp (HP for milk and body tissue production) plus HPm (HP for maintenance including pregnancy and embryo needs). The constant level of HPp 1 HPm 5 130 MJ/cow per day, found in this study, in accordance with previous data (Aharoni et al., 2005 and2006;Miron et al., 2007 unpublished), suggests that any increase in HPp of the cows is enabled by a concomitant decrease in their HPm. Thus, under severe heat load conditions without external cooling, HPm of the lactating cows might increase (see Berman, 2005) and therefore HPp should be concomitantly decreased to maintain the total HP level. ...
The objective of this study was to measure the effect of feeding two total mixed rations (TMRs), differing in their roughage content and in vitro dry matter (DM) digestibility, on the physiological response and energy balance of lactating cows. The partitioning of metabolizable energy intake (MEI) between heat production (HP) and retained energy (RE) of cows held under hot weather conditions and external evaporative cooling was measured. In all, 42 lactating cows were divided into two similar sub-groups, each of 21 animals, and were fed either a control (CON) ration containing 18% roughage neutral detergent fiber (NDF) or an experimental (EXP) TMR containing 12% roughage NDF and used soy hulls as partial wheat silage replacer. The in vitro DM digestibility of the CON and EXP TMR was 75.3% and 78.6%, respectively (P < 0.05). All cows were cooled by evaporative cooling for 2 adaptation weeks plus 6 experimental weeks under hot weather conditions. The EXP diet reduced rectal temperature and respiratory rate of the cows while increasing their DM intake (DMI) from 23.1 to 24.7 kg/cow per day, milk yield from 41.9 to 44.2 kg and yield of energy-corrected milk from 38.7 to 39.7 kg, as compared with the CON group. Cows fed the EXP TMR had increased RE in milk and body tissue, as compared with the CON group, but the diets had no effect on the measured HP that was maintained constant (130.4 v. 130.8 MJ/cow per day) in the two groups. The measured MEI (MEI = RE + HP) and the efficiency of MEI utilization for RE production were also similar in the two dietary groups.
... Thus, when animals BW and RE are measured, as used for RFI calculation, for ranking the animals according to their individual efficiency trait, the HP can replace the MEI and DMI. Following the approval of the HR-O 2 pulse to measure the HP of confined and free-grazed cattle (see Sections 4, 5, and 6), we suggest that confined and free-grazed cattle can be ranked according to their individual efficiency by using the RHP index [13,14,22]. ...
... The RHP repeatability was well validated when grazing heifers were compared under two significantly different energy-balance conditions [14]. The RHP was successfully used to test the efficiency variation of two breeds of lactating dairy cows [22], and under cowshed conditions when growing bull calves are tested in confined feedlot [13]. ...
The full potential for pasture and grazing animal production worldwide is not realized. Efficient herd management must address the mutual interaction between the pasture and the herd’s needs. Cattle grazing’ activities, forage availability, and cattle’s heat production (HP) measurements can be used to calculate the grazing herd’s energy-balance metrics and the actual consumed forage quality and can identify health and reproduction events. The forage availability index corrects the effect of a shortage of forage biomass. Direct individual HP and energy-performance measurements of grazing and confined cattle enable ranking them according to their efficiency. The methods for such measurements are available for managing grazing herds and their lands. A sample of animals can be used to characterize herds’ energy status and grazing land. Selecting grazing and confined cattle for improved efficiency and optimization of grazing land management will increase annual forage production and soil organic matter content (soil quality). As a result, the number of heads of cattle and their production per unit area will significantly increase, and greenhouse gas emissions relative to cattle production rate will decrease. Although the technologies for measuring cattle’s HP and activities are mainly commercially available, coordination between manufacturers is required.
... Energy in BCS change was calculated on base of the assumption that each unit of BCS (within the range of 2.5-3.5) corresponds on average to 30 kg of body fat reserve according to Aharoni et al. (2006). ...
... In this study, the increase of 10.2% in RE was not followed by an increase in the daily HP of the cows, which was maintained at a similar level of 141-136 MJ/cow in both groups during the 90 DIM. Support for this finding is provided from the similar levels of total HP, in the range of 123-35 MJ/cow/d, obtained in previous studies with lactating Israeli Holstein cows (Aharoni et al., 2005(Aharoni et al., , 2006Adin et al., 2008;Miron et al., 2008). As total HP is actually the sum of HPp (HP for milk and body tissue production) plus HPm (HP for maintenance including embryo development and energy loss in urine, methane and CO 2 ), the constant level of HPp + HPm of 141-136 MJ/cow/d, in this study (and in the previous studies mentioned above), suggests that there is an upper HP level that cows can tolerate. ...
This study measured the effects of including soyhulls as partial roughage replacement in total mixed rations (TMR) fed to 25 pairs of cows during early lactation, on the dry matter (DM) intake, particle kinetics, rumination, in vivo DM and NDF digestibility, milk and FCM yields, and BW changes. The 2 diets used in this study differed in the content of roughage and roughage NDF [23.5 vs. 35.0%, and 12.8 vs. 18.7% in the experimental (EXP) and control (CON) TMR, respectively]. The EXP TMR contained 20.5% less physically effective NDF than the CON TMR (11.7 vs. 14.1% of DM, respectively). These differences were expressed in a greater intake per meal (by 13.3%), a higher rate of meal intake (by 23.2%), a similar number of meals per day, a shorter daily eating duration (by 13%), and a higher total daily DMI (by 7.2%) in the EXP cows as compared with the CON cows. The in vivo DM and NDF digestibility was higher by 4.9 and 22.7%, respectively, in the EXP cows than in the CON cows. The rumination time for the TMR in the EXP cows was 12.7% (54.3 min/d) shorter than in the CON cows, and this was probably related to the difference of 12.4% in physically effective NDF intake between the 2 groups. Patterns of daily rumination and feed consumption throughout an average day showed a delay of approximately 1 to 2 h between the eating and rumination peaks. Particle flow from the rumen of the EXP cows was characterized by a longer rumen mean retention time (by 17.8%) and longer rumination time per kilogram of roughage ingested (by 23.5%) as compared with the CON cows. Thus, favorable conditions for NDF digestion were created in the rumen of the EXP cows, as reflected in their rumen pH values (6.67). The advantage of the EXP cows in intake and digestibility was reflected in a concomitant increase of 7.4% in milk production and of 9.2% in FCM yield as compared with the CON cows. No difference was found between the 2 groups with respect to efficiency of feed utilization for milk production and BW changes.
... In this way, "diluting" maintenance requirements as milk production increases and feed intake does not increase to the same extent, has been the most important driver in improving feed efficiency in the past but, its effect decreases with each successive increment in milk production relative to BW and so it will be less important in the future (VandeHaar et al., 2016). Alternatively, individual energy efficiency, regardless of the "dilution of maintenance" effect, can be evaluated by estimating the residual HP (Aharoni et al., 2006). Moreover, as shown in the present study, cows with greater residual HP will have a decreased energy retention efficiency (RE/MEI) as a greater proportion of the consumed ME will be lost as heat. ...
The objective was to evaluate the effect of the Holstein genotype (North American Holstein vs. New Zealand Holstein; NAH vs. NZH, respectively) in a pasture-based system on heat production (HP), energy partitioning between maintenance and production (milk and tissue) and energy efficiency during two different stages of lactation. Twenty-eight Holstein dairy cows (14 cows of each genotype) with similar calving date (May 5, 2018 ± 23 days) were managed in a pasture-based system and supplemented with one third of the predicted total dry matter intake as concentrate. Heat production, retained energy in milk and tissue, metabolizable energy intake (MEI) and the proportion of MEI retained in milk + tissue (RE/MEI) were measured at 115 and 192 ± 19 days in milk and residual HP was estimated by the difference between measured HP and predicted HP based on NRC (2001) model according to body weight, body condition score and milk production. The NAH cows were 60 ± 15 kg heavier and produced 4.7 ± 1.0 kg/d more milk with lower percentages of fat and protein than NZH cows. However, there were no differences in fat or protein yield per day between genotypes. Metabolizable energy intake, retained energy in milk and tissue, HP and RE/MEI were not different between genotypes at 115 days in milk. Nevertheless, at 192 days in milk the MEI, HP and residual HP were lower in NZH than NAH, whereas RE/MEI was not different when both genotypes were managed under a pasture-based system with one third of the consumed diet as concentrate. The capacity of NZH cows to maintain the same RE/MEI than NAH cows at 192 days in milk despite of the lower MEI, was due to a lower metabolizable energy requirement for maintenance (853 vs. 729 kJ/body weight0.75 per day for NAH and NZH, respectively). Indeed, the lower energy requirement for maintenance in NZH was associated with a lower fasting heat production since kl were not different between genotypes. Thus, NZH cows could have a lower proportion of their body as protein mass or a lower relative mass of the internal organs involved with digestive and circulatory functions. However, further investigation is necessary to understand the differences in maintenance energy requirements between the Holstein genotypes.
... In the present study, residual HP was negative for both groups of cows probably as HP was measure in early lactation, when feed intake is restricted and gastrointestinal viscera and liver are still growing in mass and activity (Baldwin et al., 2004) determining reduced maintenance requirements. Indeed, Aharoni et al. (2006) reported that maintenance energy requirement varied along lactation being minimum in early lactation and Ellis et al. (2006) reported an increase of 20% in maintenance requirements from the early to mid-lactation. Nevertheless, residual HP difference between G0 and G1 cows were about 10% of the estimated ME intake. ...
The aim of the study was to compare energy partitioning between heat production (HP) and retained (milk and body reserves) energy as well as energy efficiency of dairy cows assigned to different feeding strategies (with or without pasture grazing) during early lactation. At calving, 18 primiparous cows (528 ± 40 kg body weight (BW); 3.2 ± 0.2 body condition score (BCS); fall calving) were assigned in a randomized block design, during the first 61 days postpartum, to either (G0) mixed ration (PMR) ad libitum (58% forage:42% concentrate) +4.0 kg DM/d of an energy-protein concentrate in the milking parlor or (G1) grazing of alfalfa (6-h grazing in 3 days strips; 20 kg DM/d of pasture allowance) + PMR at 70% of ad libitum intake +4.0 kg DM/d of an energy-protein concentrate in the milking parlor. Diets were composed by 77% PMR and 23% concentrate for G0 cows and 54% PMR, 22% concentrate and 24% pasture for G1 cows. Heat production (HP) was measured at 40 ± 3 days postpartum by the O 2 pulse technique and energy retained (RE) in milk and body tissue was estimate based on NRC equations for the period between 26 and 54 ± 3 days postpartum. In addition, body composition was determined using the urea dilution technique at −7 and 40 ± 3 days postpartum. Absolute body water, fat and protein mass, and gross RE decreased from −7 to +40 days but the decrease in fat mass and gross RE was 10% greater for G1 than G0 cows. In addition, during this period relative lipid mass and gross energy content decreased only in the G1cows. During the second month of lactation (from 26 to 54 days), the G0 cows tended to produce 6% more milk and had 0.3 units more of BCS than the G1 cows. Both RE in milk and in body tissue were greater for G0 than G1 cows (7% and 3-fold greater, respectively). No differences were found in metabolizable energy (ME) intake and HP measured at +40 days between the cow groups. However, residual HP (difference between HP measured and predicted HP calculated from BW 0.75 and total RE on the assumption of constant efficiency coefficients), expressed as percentage of ME intake, tended to be 10% less for G0 than G1 cows. The adjusted gross energy efficiency (total RE divided by ME intake) tended to be greater for G0 than G1 cows. The results indicated that 100% PMR fed cows were more efficient, secreting more energy in the milk and retaining more energy in the body tissue than grazing cows supplemented with PMR. This was probably due to an increase of about 10% in maintenance requirements associated to greater forage content in the diet and/or grazing and walking activities in grazing cows.
... In the present study, ADG was used as a proxy of RE to calculate expected HP. In comparison, Aharoni et al. (2006) estimated RHP in cows by calculating expected HP using RE measured directly from energy of milk production and energy balance. By definition, animals with lower RHP are energetically more efficient as they produce less HP then expected based on BW and level of production. ...
This study investigated the possible mechanisms for explaining inter-animal variation in efficiency of feed utilization in intact male Holstein calves. Additionally, we examined whether the feed efficiency (FE) ranking of calves (n = 26) changed due to age and/or diet quality. Calves were evaluated during 3 periods (P1, P2 and P3) while fed a high-quality diet (calculated ME of 11.8 MJ/kg DM) during P1 and P3, and a low-quality diet (calculated ME of 7.7 MJ/kg DM) during P2. The study periods were 84, 119, 127 d, respectively. Initial ages of the calves in P1, P2, and P3 were 7, 11, and 15 mo, respectively, and initial BW were 245, 367, and 458 kg, respectively. Individual DMI, ADG, diet digestibility, and heat production (HP) were measured in all periods. The measured FE indexes were: residual feed intake (RFI), the gain-to-feed ratio (G:F), residual gain (RG), residual gain and intake (RIG), the ratio of HP-to-ME intake (HP/MEI), and residual heat production (RHP). For statistical analysis animals’ performance data in each period, were ranked by RFI, and categorized into high-, medium-, and low-RFI groups (H-RFI, M-RFI and L-RFI). RFI was not correlated with in vivo digestibility, age, BW, BCS, or ADG in all 3 periods. The L-RFI group had lowest DMI, MEI, HP, retained energy (RE) and RE/ADG. Chemical analysis of the longissimus dorsi muscle show that the L-RFI group had a higher percentage of protein and a lower percentage of fat compared to the H-RFI group. We suggested that the main mechanism separating L- from H-RFI calves is the protein-to-fat ratio in the deposited tissues. When efficiency was related to kg/d (DMI and ADG) and not to daily retained energy, the selected efficient L-RFI calves deposited more protein and less fat per daily gain than less efficient H-RFI calves. However, when the significant greater heat increment and maintenance energy requirement of protein compared to fat deposition in tissue were considered, we could not exclude the hypothesis that variation in efficiency is partly explained by efficient energy utilization. The ranking classification of calves to groups according to their RFI efficiency was independent of diet quality and age.
... A possible explanation to the difference observed on TT between the genotypes (Figure 3) could be the better adaptation of the H cows to the environment when compared with the HM cows, that represent a newer genotype in the area of study. The higher TT during nighttime of HM cows could be the resultant of a lower capacity to dissipate the heat accumulated during daytime, as demonstrated by Aharoni et al (2006) who compared H vs. HM dairy cows during the summer season in Jordan. These authors reported differences between H and HM in their diurnal patterns of heat production, suggesting that heat tolerance of HM was lower than H cows. ...
Heat stress has been recognised as a serious problem in dairy farms. The study goal was to assess the effects of climatic conditions on physiological and behavioural responses of dairy cows in Central Chile. Data of tympanic temperature (TT), panting score, respiration rate (RR), and shade utilization of cows from two genotypes, Holstein (H) and Holstein x Montbeliarde (HM), were collected twice per day (AM/PM) during three periods of the summer season in Central Chile. Moreover, three thermal comfort indices: Comprehensive climate index (CCI), temperature humidity-index (THI), and adjusted THI were estimated using meteorological data. The hour of each day was classified as “Normal” or “Stressful” based on CCI threshold of 25 °C. Statistical analysis included ANOVA, repeated measures analysis and Chi square test (a=0.05). There was an interaction of genotype x CCI condition x period (P=0.0026) with the highest TT of both genotypes under a stressful condition within each period. In addition, interactions of genotype x hour (P<0.0001) and genotype x CCI condition (P<0.0002) were also observed. The HM cows showed greater TT than H cows in both CCI conditions. The RR was higher during the afternoon and a greater proportion of cows used shade at “Mild” and “Moderate” CCI categories (P<0.001). Both genotypes showed some degree of heat stress, but cool nights and shade seem to be enough to allow to cows’ cope with the challenging diurnal conditions observed in the summer season. A study of these effects on milk production is necessary to confirm or discard the previous.
... However, Aharoni et al. (2003) observed that EHP increased proportionally with RFI in lactating cows. Furthermore, Aharoni et al. (2006) studied EHP to characterize use efficiency of protein and NE in Holstein or Holstein × Montbeliarde and observed that crossed steers had lower HR but that this was not reflected in differences in O 2 P and heat production. Table 5. Mean, SD, and range of heart rate, oxygen consumption, and heat production traits of 18 Nellore steers during the feed efficiency evaluation period Table 6. ...
The objective of this study was to examine the relationship of efficiency indices with performance, heart rate, oxygen consumption, blood parameters, and estimated heat production (EHP) in Nellore steers. Eighteen steers were individually lotfed diets of 2.7 Mcal ME/kg DM for 84 d. Estimated heat production was determined using oxygen pulse (O2P) methodology, in which heart rate (HR) was monitored for 4 consecutive days. Oxygen pulse was obtained by simultaneously measuring HR and oxygen consumption during a 10-to 15-min period. Efficiency traits studied were feed efficiency (G:F) and residual feed intake (RFI) obtained by regression of DMI in relation to ADG and midtest metabolic BW (RFIREG). Alternatively, RFI was also obtained based on equations reported by the NRC’s Nutrient Requirements of Beef Cattle to estimate individual requirement and DMI (RFI calculated by the NRC [1996] equation [RFINRC]). The slope of the regression equation and its significance was used to evaluate the effect of efficiency indices (RFIREG, RFINRC, or G:F) on the traits studied. A mixed model was used considering RFIREG, RFINRC, or G:F and pen type as fixed effects and initial age as a covariate. For HR and EHP variables, day was included as a random effect. There was no relationship between efficiency indices and back fat depth measured by ultrasound or daily HR and EHP (P > 0.05). Because G:F is obtained in relation to BW, the slope of G:F was positive and significant (P < 0.05). Regardless of the method used, efficient steers had lower DMI (P < 0.05). The initial LM area was indirectly related to RFIREG and RFINRC (P < 0.05); however, the final muscle area was related to only RFINRC. Oxygen consumption per beat was not related to G:F; however, it was lower for RFIREG-and RFINRC-efficient steers, and consequently, oxygen volume (mL·min-1·kg-0.75) and O2P (μL O2·beat-1·kg-0.75) were also lower (P < 0.05). Blood parameters were not related to RFIREG and RFINRC (P > 0.05); however, G:F-efficient steers showed lower hematocrit and hemoglobin concentrations (P < 0.05). Differences in EHP between efficient and inefficient animals were not directly detected. Nevertheless, differences in oxygen consumption and O2P were detected, indicating that the O2P methodology may be useful to predict growth efficiency. © 2015 American Society of Animal Science. All rights reserved.
... Alternative techniques to respiratory chambers are enabling scientists to collect or record gas measurements from cattle in their own production settings (e.g., grazing, free stall). Specific examples include quantifications of (1) heat production (HP) from O 2 consumption per heartbeat (Brosh et al., 1998;Aharoni et al., 2006), (2) energy expenditure using the 13 C bicarbonate technique coupled with O 2 consumption and respiratory quotient (RQ; Junghans et al., 2007;Kaufmann et al., 2011), (3) carbon emissions using tracer techniques (Stewart et al., 2008;Madsen et al., 2010), and (4) CO 2 flux (QCO 2 ) and CH 4 flux (QCH 4 ) in animal breath (Branco et al., 2015;Dorich et al., 2015;Huhtanen et al., 2015). ...
The objective of this study was to use spot short-term measurements of CH4 (QCH4) and CO2 (QCO2) integrated with backward dietary energy partition calculations to estimate dry matter intake (DMI) in lactating dairy cows. Twelve multiparous cows averaging 173 ± 37 d in milk and 4 primiparous cows averaging 179 ± 27 d in milk were blocked by days in milk, parity, and DMI (as a percentage of body weight) and, within each block, randomly assigned to 1 of 2 treatments: ad libitum intake (AL) or restricted intake (RI = 90% DMI) according to a crossover design. Each experimental period lasted 22 d with 14 d for treatments adaptation and 8 d for data and sample collection. Diets contained (dry matter basis): 40% corn silage, 12% grass-legume haylage, and 48% concentrate. Spot short-term gas measurements were taken in 5-min sampling periods from 15 cows (1 cow refused sampling) using a portable, automated, open-circuit gas quantification system (GreenFeed, C-Lock Inc., Rapid City, SD) with intervals of 12 h between the 2 daily samples. Sampling points were advanced 2 h from a day to the next to yield 16 gas samples per cow over 8 d to account for diurnal variation in QCH4 and QCO2. The following equations were used sequentially to estimate DMI: (1) heat production (MJ/d) = (4.96 + 16.07 ÷ respiratory quotient) × QCO2; respiratory quotient = 0.95; (2) metabolizable energy intake (MJ/d) = (heat production + milk energy) ± tissue energy balance; (3) digestible energy (DE) intake (MJ/d) = metabolizable energy + CH4 energy + urinary energy; (4) gross energy (GE) intake (MJ/d) = DE + [(DE ÷ in vitro true dry matter digestibility) - DE]; and (5) DMI (kg/d) = GE intake estimated ÷ diet GE concentration. Data were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) and Fit Model procedure in JMP (α = 0.05; SAS Institute Inc.). Cows significantly differed in DMI measured (23.8 vs. 22.4 kg/d for AL and RI, respectively). Dry matter intake estimated using QCH4 and QCO2 coupled with dietary backward energy partition calculations (Equations 1 to 5 above) was highest in cows fed for AL (22.5 vs. 20.2 kg/d). The resulting R(2) were 0.28 between DMI measured and DMI estimated by gaseous measurements, and 0.36 between DMI measured and DMI predicted by the National Research Council model (2001). Results showed that spot short-term measurements of QCH4 and QCO2 coupled with dietary backward estimations of energy partition underestimated DMI by 7.8%. However, the approach proposed herein was able to significantly discriminate differences in DMI between cows fed for AL or RI.
... However, Aharoni et al. (2003) observed that EHP increased proportionally with RFI in lactating cows. Furthermore, Aharoni et al. (2006) studied EHP to characterize use efficiency of protein and NE in Holstein or Holstein × Montbeliarde and observed that crossed steers had lower HR but that this was not reflected in differences in O 2 P and heat production. Table 5. Mean, SD, and range of heart rate, oxygen consumption, and heat production traits of 18 Nellore steers during the feed efficiency evaluation period Table 6. ...
The objective of this study was to examine the relationship of efficiency indices with performance, heart rate, oxygen consumption, blood parameters, and estimated heat production (EHP) in Nellore steers. Eighteen steers were individually lot-fed diets of 2.7 Mcal ME/kg DM for 84 d. Estimated heat production was determined using oxygen pulse (OP) methodology, in which heart rate (HR) was monitored for 4 consecutive days. Oxygen pulse was obtained by simultaneously measuring HR and oxygen consumption during a 10- to 15-min period. Efficiency traits studied were feed efficiency (G:F) and residual feed intake (RFI) obtained by regression of DMI in relation to ADG and midtest metabolic BW (RFI). Alternatively, RFI was also obtained based on equations reported by the NRC's to estimate individual requirement and DMI (RFI calculated by the NRC [1996] equation [RFI]). The slope of the regression equation and its significance was used to evaluate the effect of efficiency indices (RFI, RFI, or G:F) on the traits studied. A mixed model was used considering RFI, RFI, or G:F and pen type as fixed effects and initial age as a covariate. For HR and EHP variables, day was included as a random effect. There was no relationship between efficiency indices and back fat depth measured by ultrasound or daily HR and EHP ( > 0.05). Because G:F is obtained in relation to BW, the slope of G:F was positive and significant ( < 0.05). Regardless of the method used, efficient steers had lower DMI ( < 0.05). The initial LM area was indirectly related to RFI and RFI ( < 0.05); however, the final muscle area was related to only RFI. Oxygen consumption per beat was not related to G:F; however, it was lower for RFI- and RFI-efficient steers, and consequently, oxygen volume (mL·min·kg) and OP (μL O·beat·kg) were also lower ( < 0.05). Blood parameters were not related to RFI and RFI ( > 0.05); however, G:F-efficient steers showed lower hematocrit and hemoglobin concentrations ( < 0.05). Differences in EHP between efficient and inefficient animals were not directly detected. Nevertheless, differences in oxygen consumption and OP were detected, indicating that the OP methodology may be useful to predict growth efficiency.
... Energetic efficiency varies considerably among breeds, as well as among different individuals from the same breed (Ferrell and Jenkins 1985;Thiessen et al. 1985;Taylor et al. 1986;Solis et al. 1988;Aharoni et al. 2006). The nature of this variation is not entirely clear, but various factors are thought to affect the animal's RFI and hence its energy utilization (Johnson et al. 2003). ...
Ruminants hold enormous significance for man as a source of milk and meat. Their remarkable ability to convert indigestible plant mass into these digestible food products is the outcome of a symbiosis that resides in the reticulorumen—an anaerobic double-chambered compartment in the ruminant digestive system. The reticulorumen houses a complex microbiota which is responsible for the degradation of plant material consisting mainly of indigestible sugar polymers such as cellulose and hemicelluloses, consequently enabling the conversion of plant fibers into chemical compounds that are absorbed and digested by the animal. This cooperative relationship between the ruminant and its resident ruminal microorganisms evolved over millions of years and has implications for our everyday lives with respect to food, environment, renewable energy and economics. Ruminants hold enormous significance for man as they can convert energy stored in plant mass, which is mainly indigestible for humans, to digestible food products. Because of this trait, ruminants have been extremely important in the evolution of human civilizations via their effects on the development of hunting and agricultural societies (White LA (2007) The evolution of culture: the development of civilization to the fall of Rome. Left Coast Press, Walnut Creek, CA). Today, a significant proportion of domesticated animal species worldwide—the source for most meat and dairy products—are ruminants. Hence, an understanding of this complex ecosystem is of major interest. This chapter discusses several aspects of this ecosystem: the physiology of the ruminant digestive system and its suitability for cooperative interaction with its resident microbiota, the composition of overall rumen metabolism and its role in ruminant well-being, the ruminal microbial populations, their interactions with each other, their importance and effects on the host, and their acquisition after birth.
... The energetic efficiency varies considerably between breeds, as well as between different individuals from the same breed (Ferrell and Jenkins. 1985;Thiessen and Taylor 1985;Taylor et al. 1986;Solis et al. 1988;Aharoni et al. 2006). The nature of this variation is not entirely clear: various factors are thought to affect the animal's RFI and hence its energy utilization (Johnson et al. 2003). ...
Dairy cattle hold enormous significance for man as they convert the energy stored in indigestible plant mass into milk and meat, which are digestible and consumed worldwide. The efficiency with which an individual cow converts the energy stored in its feed into food products, termed feed efficiency, is thought to be stable; however, for reasons poorly understood, it varies considerably between cows. One factor that could markedly affect dairy cow feed efficiency is its residing microbiota which, in ruminants, is responsible for most of the food’s digestion and absorption. The microbes are mainly situated within the first compartment of the digestive tract – the reticulorumen. Recent studies connecting methane emission, clustering, and diversity of microbial populations with the cow’s feed efficiency strongly imply that the reticulorumen microbiota is correlated with cows’ energy utilization. Hence, understanding the relationship between the reticulorumen microbiota and cows’ feed efficiency may favor more energy-efficient microbiomes, and therefore increase fiber degradation, elevate reticulorumen microbial protein concentration, reduce methane emission, and consequentially improve cow productivity.
... Alternative techniques to respiratory chambers are enabling scientists to collect or record gas measurements from cattle in their own production settings (e.g., grazing, free stall). Specific examples include quantifications of (1) heat production (HP) from O 2 consumption per heartbeat (Brosh et al., 1998; Aharoni et al., 2006), (2) energy expenditure using the 13 C bicarbonate technique coupled with O 2 consumption and respiratory quotient (RQ; Junghans et al., 2007; Kaufmann et al., 2011), (3) carbon emissions using tracer techniques (Stewart et al., 2008; Madsen et al., 2010), and (4) CO 2 flux (QCO 2 ) and CH 4 flux (QCH 4 ) in animal breath (Branco et al., 2015; Dorich et al., 2015; Huhtanen et al., 2015). A portable, automated, open-circuit gas quantification system (GQS; GreenFeed; C-Lock Inc., Rapid City, SD) has been used recently to obtain spot shortterm measurements of QCH 4 and QCO 2 in near realtime mode and with minimal disturbance to the natural behavior of the cow (Branco et al., 2015; Dorich et al., 2015; Huhtanen et al., 2015). ...
Abstract Text:
Real time measurements of CH4 (QCH4) and CO2 (QCO2) fluxes were used in a pilot study to estimate heat production1 (HP) and energy conversion efficiency in lactating dairy cows. Oxygen utilization (QO2) was estimated according to the respiration quotient2. Eleven multiparous and 4 primiparous lactating Holstein cows averaging 176 ± 34 DIM, 42.9 ± 6.8 kg of milk yield and 681 ± 48 kg of BW were blocked by DIM, parity, and DMI (as % of BW) and, within each block, randomly assigned to 1 of 2 treatments: restricted intake (RI) (90% DMI) or ad libitum intake (AI) according to a crossover design. Each experimental period lasted 22 d with 14 d for treatments adaptation and 8 d for data and sample collection. Diets contained (DM basis): 40% corn silage, 12% grass-legume haylage, and 48% concentrate. Spot gas measurements were taken in 5-min sampling periods from all cows using a portable automated head chamber system [GreenFeed® (GF); C-Lock Inc., Rapid City, SD] with intervals of 12 h between the 2 daily samplings. Sampling points were advanced 2 h from a day to the next to yield 14 gas samplings/cow over 7 d to account for diurnal variation in QCH4 and QCO2. Data were analyzed using the Fit Model procedure in JMP, and least square means are reported. Cows on RI converted more feed gross energy3 into milk energy4 (28.3 vs. 27.0%, SEM = 0.63; P = 0.04) and more DMI into metabolizable energy5 than AI cows (11.8 vs. 11.3 MJ/kg of DMI; SEM = 0.22 P = 0.02). Conversely, RI cows yielded more HP/kg of DMI (6.65 vs. 6.36 MJ/kg; SEM = 0.18; P = 0.04). Our results suggest that the proposed methodology has potential to identify more efficient dairy cows according to real time measurements of QCH4 and QCO2 using the GF.
Equations used for estimations:
1Estimated HP MJ/cow/d = [(3.86 × QO2) + (1.2 × QCO2) – (0.518 × QCH4)] × 4.184/1000 (Brouwer, 1965)
2QO2/QCO2 = 0.95 (Madsen et al., 2010)
3Gross energy intake MJ/cow/d = [dietary CP% × DMIkg × 17 × 0.6] × 4.184 (IPCC, 2006)
4Milk energy MJ/cow/d = [(0.384 × fat%) + (0.223 × protein%) + (0.199 × lactose%) – 0.108] × milk yield kg/cow/d (AFRC, 1993)
5Metabolizable energy MJ/cow/d = HP + Milk energy ± (19.99 × kg of mobilized weight) (AFRC, 1990)
Keywords: energy conversion efficiency, heat production, GreenFeed
... An Israeli study (Aharoni et al., 2006) compared the heart rates and oxygen consumption of 7 multiparous MO × HO crossbred cows and 7 multiparous pure HO cows during two 10-d periods. Their equations predicted that MO × HO cows had lower ME intake than pure HO cows; however, MO × HO cows also had less gross efficiency, because MO × HO cows were penalized for having greater BCS and BW. ...
Montbéliarde (MO)-sired crossbred cows (n = 57) were compared with pure Holstein (HO) cows (n = 40) for dry matter intake (DMI), production, hip height, body condition score (BCS), and body weight (BW) during the first 150 d of first lactation. Also, production for 305 d was compared for first lactation. The MO-sired crossbred cows were composed of MO × HO cows (n = 33) and MO × Jersey/HO cows (n = 24). Cows were individually fed a total mixed ration twice daily. The DMI was measured for the first 150 d of lactation, except from d 1 to 3 postpartum to permit cows to acclimate to stalls in a confinement barn. Hip height was measured once between 20 and 172 d postpartum, and BCS and BW were recorded every other week. The MO-sired crossbred cows did not differ from the pure HO cows for 150-d DMI, 150-d fat plus protein production, or for 305-d fat plus protein production. Hip height was similar for MO × HO and pure HO cows, but MO × Jersey/HO cows had shorter hip height than the pure HO cows. Despite the lack of difference for DMI, the MO-sired crossbred cows had significantly greater BCS (3.30 vs. 2.74) and BW (551 vs. 528 kg) than the pure HO cows. The MO-sired crossbred cows (122 d) had fewer days open than the pure HO cows (150 d). The higher BCS of the MO-sired crossbred cows, especially during early lactation, may have provided an advantage for fertility. Differences for DMI between breed groups were not studied for the latter half of first lactation or for multiparous cows.
Prof. Dr. habil. Wilfried Brade (Hannover)
Einleitung
Alle Lebensprozesse sind mit der Erzeugung thermischer Energie (= Wärmeenergie) und der notwendigen Abgabe dieser Energie an die unmittelbare Umgebung verbunden. Die Wärmeproduktion (WP) stellt bei laktierenden Milchkühen einen bemerkenswert hohen Anteil nichtnutzbarer Futterenergie dar. Die Gesamt-WP resultiert aus der Wärmebildung im Rahmen der Verdauung aufgenommener Nährstoffe, notwendiger körperlicher Aktivitäten (z.B. Bewegung) und der Milchsynthese. Die in den letzten Jahren erzielten Leistungssteigerungen-basierend auf einer weiteren Zunahme der Stoffwechselaktivität der Milchkühe-sind mit einer spürbaren Erhöhung der Wärmebildung je Kuh/Laktation verbunden. Vor dem Hintergrund des Klimawandels wird diese Thematik nun auch in der deutschen Rinderzüchtung immer wichtiger.
Until recently, measurements of energy expenditure (EE; herein defined as heat production) in respiration chambers did not account for the extra energy requirements of grazing dairy cows on pasture. As energy is first limiting in most pasture-based milk production systems, its efficient use is important. Therefore, the aim of the present study was to compare EE, which can be affected by differences in body weight (BW), body composition, grazing behavior, physical activity, and milk production level, in 2 Holstein cow strains. Twelve Swiss Holstein-Friesian (HCH; 616 kg of BW) and 12 New Zealand Holstein-Friesian (HNZ; 570 kg of BW) cows in the third stage of lactation were paired according to their stage of lactation and kept in a rotational, full-time grazing system without concentrate supplementation. After adaption, the daily milk yield, grass intake using the alkane double-indicator technique, nutrient digestibility, physical activity, and grazing behavior recorded by an automatic jaw movement recorder were investigated over 7 d. Using the 13C bicarbonate dilution technique in combination with an automatic blood sampling system, EE based on measured carbon dioxide production was determined in 1 cow pair per day between 0800 to 1400 h. The HCH were heavier and had a lower body condition score compared with HNZ, but the difference in BW was smaller compared with former studies. Milk production, grass intake, and nutrient digestibility did not differ between the 2 cow strains, but HCH grazed for a longer time during the 6-h measurement period and performed more grazing mastication compared with the HNZ. No difference was found between the 2 cow strains with regard to EE (291 ± 15.6 kJ) per kilogram of metabolic BW, mainly due to a high between-animal variation in EE. As efficiency and energy use are important in sustainable, pasture-based, organic milk-production systems, the determining factors for EE, such as methodology, genetics, physical activity, grazing behavior, and pasture quality, should be investigated and quantified in more detail in future studies.
The objective of this study was to measure the effect of feeding two total mixed rations (TMRs), differing in their roughage content and in vitro dry matter digestibility, on the respiratory rate, body temperature, eating behavior and energy balance of lactating cows. The partitioning of metabolizable energy intake (MEI) between heat production (HP) and retained energy (RE) of cows held under heat load conditions was measured. Forty-two lactating cows were divided into two similar sub-groups, each of 21 animals, and were fed either a control (CON) ration containing 18% roughage neutral detergent fiber (NDF) or an experimental (EXP) TMR that contained 12% roughage NDF and used soy hulls as partial wheat silage replacer. The in vitro DM digestibility of the CON and EXP TMRs was 75.3 and 78.6%, respectively (P
This study measured the effects of replacing corn silage and vetch hay by soy hulls in total mixed rations (TMRs) fed to 25 pairs of cows through 90d in milk, on dry matter (DM) intake, in vivo digestibility, milk yield and composition, onset of normal estrous activity, body condition score (BCS), health and the energy balance of lactating cows. The partitioning of metabolizable energy (ME) intake between heat production (HP) and retained energy (RE) in milk and body change of each cow was measured. The two TMRs differed in the content of forage and forage aNDFom [235g/kg versus 350g/kg; and 128g/kg versus 187g/kg DM, in the experimental (EXP) and control (CON) diets, respectively]. This was reflected by an increase in voluntary DM intake by 7.2% (P=0.02) in the EXP group as compared with the CON. In vivo DM and aNDFom digestibility were 4.9% (P=0.03) and 22.7% higher (P=0.01), respectively, in the EXP group than in the CON. The higher DM intake and digestibility of the EXP TMR were reflected by a concomitant increase of 7.4% in milk yield and 10.8% in RE (P=0.01) of the EXP cows as compared with the CON. The two dietary groups expressed similar somatic cell counts, and metabolic disorders (i.e., ketosis and/or lameness), as well as pedometer activity (steps/h) suggesting similar udder health, behavior and animal welfare. A trend to an earlier return to normal ovarian activity occurred in the EXP cows as reflected by fewer days to 1st ovulation and advanced outset of estrous cycle. Despite the higher RE of the EXP cows, the HP of both groups was maintained at an upper level of 141–136MJ/cow/d during the 90d of the experiment.
A major part of the ME consumed by ruminants (MEI) is dissipated as heat. This fraction, called heat production or energy expenditure (EE), is assayed largely by measuring O2 consumption (VO2). Conventional measurement of EE in controlled conditions in chambers does not reflect the complexity of natural, environmental, and social conditions of free-ranging animals. In mammals, most of the measured VO2 is transferred to the tissues through the heart; therefore, regression of heart rate (HR) against VO2 can be used to estimate the EE of free-ranging animals. The present article reviews the current knowledge on the use of HR for estimating EE. Energy expenditure can be determined from HR measurements, recorded daily over the course of several days, multiplied by the VO2 per beat. When an animal does not perform significant exercise, a constant value of VO2 per beat [O2 pulse (O2P)] measured over a short period (10 to 15 min) is used; during exercise, O2P increases, and the regression equation of VO2 against HR is used. Under extreme heat load, HR increases to improve heat dissipation, and O2P decreases; therefore, the effect of heat load on O2P needs to be taken into account. Cold stress that doubles heat production does not affect O2P. Heart rate and EE are highly correlated with MEI, but there is significant individual variation in the relationship; therefore, the daily change in the HR of individual animals can be used as an indicator of changes in the individual energy status of a ruminant, and the average HR of the group can serve in the estimation of the energy status of the group. When O2P is measured, the average group EE is an indication of the energy balance of the whole group. Because the MEI of nondraft animals is the sum of EE and retained energy (RE), the MEI of free-ranging ruminants can be determined by measurement of EE by the HR method and adding the RE. Similarly, the RE can be determined without slaughtering the animals from measurements of EE and MEI. Soon when devices for automatic HR monitoring of domestic ruminants become available at a reasonable price, continuous monitoring of HR might provide producers with a sensitive tool for identifying changes in the energy status of their animals. This will also significantly help to shorten the time needed to identify health problems of individual animals.
This experiment investigated whether divergent selection on postweaning residual feed intake (RFI) resulted in differences in steer growth, feed intake and feed efficiency over a 70-day test period in the feedlot, and in carcass attributes at slaughter. Selection for low postweaning RFI (high efficiency line, HE) produced steer progeny that ate less per unit liveweight gain compared to steers from high RFI (low efficiency line, LE) parents, with no adverse effects on growth. The HE steers tended to have lower feed conversion ratio (feed:gain; FCR) than the LE steers (7.6 v 8.2 kg/kg; P<0.1) and had lower RFI (-0.12 v 0.10kg/day; P<0.05). Significant positive regressions of FCR and RFI with mid-parent estimated breeding value for RFI (EBV RFI) provided further evidence for favourable genetic associations with postweaning RFI. Ultrasound measurement before slaughter showed that HE steers had less depth of fat over their rib and rump and a smaller cross-sectional area of the eye-muscle than LE steers (10.2 v 11.6mm, 13.1 v 14.8mm, 66.9 v 70.6cm 2 ; all P<0.05). The HE steers had less fat depth at the rump on the hot carcass and there was a small difference in dressing percentage (14.9 v 16.5mm, 52.1 v 52.9%; both P<0.05). Significant (P<0.05) regressions for the three subcutaneous fat measurements, eye-muscle area and dressing percentage with mid-parent EBV RFI provided additional evidence of genetic association. There were no differences (P>0.05) between HE and LE steer progeny in hot carcass weight or in predicted retail beef yield. INTRODUCTION Feeding cattle is a major cost of beef production. Residual (or net) feed intake (RFI) has been proposed as a measure of feed efficiency that is independent of liveweight (LW) and growth rate. It is calculated as the amount of feed consumed net of that predicted based on LW and growth rate. Cattle with low RFI eat less than expected for their LW and growth rate and are therefore more efficient than cattle with high RFI. Postweaning tests of young bulls and heifers from a number of British beef breeds have shown RFI to be heritable (Arthur et al. 2001a) and to respond to selection (Arthur et al. 2001b). This experiment investigated whether divergent selection on postweaning RFI resulted in differences in steer growth, feed intake and feed efficiency in the feedlot, and in carcass attributes at slaughter.
The benefit of recording net feed intake (NFI) in industry breeding schemes was investigated using a model of investment and gene flow resulting from selection activities. The results showed that where the breeding objective targets the high quality Japanese market, it is profitable to record NFI on all bulls in the seedstock sector where NFI measurement costs are as high as 150 per animal, and is not profitable at higher measurement costs. However, with more efficient breeding scheme designs, measurement of NFI on a proportion of bulls may be profitable, even when measurement costs are greater than $150 and the domestic grass-fed market is targeted. Further work is required to provide recommendations to breeders as to how this trait should be incorporated into breeding programs.
Experiments on Angus steer progeny following a single generation of divergent selection for residual feed intake suggest that there are many physiological mechanisms contributing to variation in residual feed intake. Difference in energy retained in protein and fat accounted for only 5% of the difference in residual feed intake following divergent selection. Differences in digestion contributed (conservatively) 10% and feeding patterns 2% to the variation in residual feed intake. The heat increment of feeding contributed 9% and activity contributed 10%. Indirect measures of protein turnover suggest that protein turnover, tissue metabolism and stress contributed to at least 37% of the variation in residual feed intake. About 27% of the difference in residual feed intake was due to variation in other processes such as ion transport, not yet measured. It is hypothesised that susceptibility to stress is a key driver for many of the biological differences observed following divergent selection for residual feed intake in beef cattle. Further research is required to accurately quantify the effect of selection for improved residual feed intake on protein turnover, tissue metabolism and ion transport, and to confirm the association between stress susceptibility and residual feed intake in beef cattle.
Additive and nonadditive genetic effects on lifetime yields of milk and milk components and lifetime profitability were estimated from 5070 cattle in a Holstein pureline, an Ayrshire-based pureline, and 10 crossbred groups of these purelines. Lifetime yields of milk, fat, protein, and lactose and lifetime milk value and annualized discounted net returns were analyzed. Lifetime yields, lifetime milk value, and annualized discounted net returns of the Holstein x Ayrshire-based line F1 and an F1 x (F1 x F1) cross were not significantly different from those for the Holstein pureline. Net reproductive rate for F1 females was 9% greater than that of contemporary Holsteins. The Holstein pureline was superior to the Ayrshire-based pureline for direct additive genetic merit for all traits. Heterosis for the lifetime traits ranged from 16.6% for lifetime milk yield to 20.6% for annualized discounted net returns. Cytoplasmic maternal effect on annualized discounted net return was significant and favored the Ayrshire-based line. Potential economic benefit may derive from development of a crossbred cow that is superior to Holsteins. Maximum exploitation of additive and nonadditive genetic effects on lifetime yields and profitability appears to favor a rotational crossbreeding system with two breeds.
Ten growing heifers were either exposed to or protected from solar radiation, offered a diet of either high (H) or low (L) ME, and fed either in the morning or afternoon during a hot summer. Heifers that consumed the H diet had a greater water intake, DMI, metabolizable energy intake, energy expenditure, and retained energy than heifers that consumed the L diet. Solar radiation did not have an effect on any of these variables. Furthermore, dietary energy and time of measurement had an effect on rectal temperature (Tr), respiration rate (RR), heart rate (HR), and rate of oxygen uptake (VO2); solar radiation had an effect on Tr and RR but not on HR and VO2; and time of feeding had an effect only on VO2. Heifers coped with greater heat loads by increasing RR and the difference in Tr between morning and afternoon. It seems that a lowered body temperature in the morning is a physiological mechanism used by animals to prepare for the heat load that develops during the day. Heat production (HP) and HR throughout the day were affected mainly by the time of feeding and not by the environmental heat load. Feeding in the afternoon increased HP in the cooler hours of the day when heat losses from the animal through conduction and radiation were more efficient. With a pending high heat load situation, reducing feed quality and(or) changing the time of feeding to the late afternoon could be beneficial to the animals in reducing their heat loads.
We examined whether heart rate (HR) could be used to estimate energy expenditure (EE) in cattle. Six Hereford heifers (345 +/- 10.8 kg BW) 12 mo of age were implanted with HR radio transmitters and maintained in individual pens under the following treatments: 1) shade or sun exposure, 2) high- or low-energy diet, and 3) feeding in morning or afternoon. The HR of animals was measured every .5 h during 3 mo; measurements of oxygen consumption and HR were made simultaneously in the morning and in the afternoon while animals were resting and exercising. Average daily HR (52 +/- 4 beats/min) and average daily EE (380 +/- 9 kJ/kg(.75)) in animals on the low-energy diet were less than values in animals on the high-energy diet (94 +/- 4 beats/min and 653 +/- 9 kJ/ kg(.75), respectively). For each animal and within each diet, linear regressions best described the relationship between HR and EE in resting animals, whereas quadratic regressions best described this relationship for exercising animals. The quadratic equation for the exercising animals could also be used for resting animals. In addition, a constant value of EE per heart beat (EE pulse) for each individual resting animal was found and gave accurate estimations. This method was convenient because 1) no exercise equipment was needed to generate the regression equations and 2) EE pulse was less affected by diet than was EE estimated by regression equations. We conclude that HR, a relatively easy measurement, can be useful and accurate in estimating EE. To increase the accuracy of the estimation of EE by HR, the relationship of HR to EE should be established for each animal. In addition, the nutritional regimen for the animal in which EE is estimated should be used for the animal in establishing the relationship.
The aim of this study was to evaluate the profitability of dairy herds under three mating systems involving the Holstein-Friesian, Jersey, and Ayrshire breeds. Mating systems were straight breeding and rotational cross-breeding using two or three breeds. A deterministic model was developed to simulate the nutritional, biological, and economic performance of dairy herds under New Zealand conditions. Expected performances per cow were obtained using estimates of breed group and heterosis effects, age effects, and age distribution in the herd. Requirements for dry matter in feed were estimated per cow for maintenance, lactation, pregnancy, and growth of the replacements. Stocking rate was calculated by assuming 12,000 kg of dry matter utilized annually per hectare. Productivity per hectare was calculated as performance per cow multiplied by stocking rate. Profitability was the difference between income (sale of milk and salvage value of animals) and costs (related to the number of cows in the herd and the land area farmed). Under current market values for milk and meat, all of the rotational crossbred herds showed superior profitability to the straightbred herds (Holstein-Friesian x Jersey, NZ493/ha; Jersey x Ayrshire, NZ430/ha; Jersey, NZ398/ha; and Ayrshire, NZ$338/ha). Changes in the value for fat relative to protein affected profitability more significantly in herds using the Jersey breed, and changes in the value for meat affected profitabiity more significantly in herds using the Holstein-Friesian and Ayrshire breeds. Results suggested that, under New Zealand conditions, the use of rotational crossbreeding systems could increase profitability of dairy herds under the conceivable market conditions.
Records on 1,180 young Angus bulls and heifers involved in performance tests were used to estimate genetic and phenotypic parameters for feed intake, feed efficiency, and other postweaning traits. The mean age was 268 d at the start of the performance test, which comprised 21-d adjustment and 70-d test periods. Traits studied included 200-d weight, 400-d weight, scrotal circumference, ultrasonic measurements of rib and rump fat depths and longissimus muscle area, ADG, metabolic weight, daily feed intake, feed conversion ratio, and residual feed intake. For all traits except the last five, additional data from the Angus Society ofAustralia pedigree and performance database were included, which increased the number of animals to 27,229. Genetic (co)variances were estimated by REML using animal models. Direct heritability estimates for 200-d weight, 400-d weight, rib fat depth, ADG, feed conversion,and residual feed intake were 0.17 +/- 0.03, 0.27 +/- 0.03, 0.35 +/- 0.04, 0.28 +/- 0.04, 0.29 +/- 0.04, and 0.39 +/- 0.03, respectively. Feed conversion ratio was genetically (r(g) = 0.66 ) and phenotypically (r(p) = 0.53) correlated with residual feed intake. Feed conversion ratio was correlated (r(g) = -0.62, r(p) = -0.74) with ADG, whereas residual feed intake was not (rg = -0.04, r(p) = -0.06). Genetically, both residual feed intake and feed conversion ratio were negatively correlated with direct effects of 200-d weight (r(g) = -0.45 and -0.21) and 400-d weight (r(g) = -0.26 and -0.09). The correlations between the remaining traits and the feed efficiency traits were near zero, except between feed intake and feed conversion ratio (r(g) = 0.31, r(p) = 0.23), feed intake and residual feed intake (r(g) = 0.69, r(p) = 0.72), and rib fat depth and residual feed intake (r(g) = 0.17, r(p) = 0.14). These results indicate that genetic improvement in feed efficiency can be achieved through selection and, in general, correlated responses in growth and the other postweaning traits will be minimal.
Heterosis and breed differences were estimated for milk yield traits, somatic cell score (SCS), and productive life (PL), a measure of longevity. Yield trait data were from 10,442 crossbreds and 140,421 purebreds born since 1990 in 572 herds. Productive life data were from 41,131 crossbred cows and 726,344 purebreds born from 1960 through 1991. The model for test-day yields and SCS included effects of herd-year-season, age, lactation stage, regression on sire's predicted transmitting ability, additive breed effects, heterosis, and recombination. The model for PL included herd-year-season, breed effects, and general heterosis. All effects were assumed to be additive, but estimates of heterosis were converted to a percentage of the parent breed average for reporting. Estimates of general heterosis were 3.4% for milk yield, 4.4% for fat yield, and 4.1% for protein yield. A coefficient of general recombination was derived for multiple-breed crosses, but recombination effects were not well estimated and small gains, not losses, were observed for yield traits in later generations. Heterosis for SCS was not significant. Estimated heterosis for PL was 1.2% of mean productive life and remained constant across the range of birth years. Protein yield of Brown Swiss x Holstein crossbreds (0.94 kg/d) equaled protein yield of purebred Holsteins. Fat yields of Jersey x Holstein and Brown Swiss x Holstein crossbreds (1.14 and 1.13 kg/d, respectively) slightly exceeded that of Holsteins (1.12 kg/d). With cheese yield pricing and with all traits considered, profit from these crosses exceeded that of Holsteins for matings at breed bases. For elite matings, Holsteins were favored because the range of evaluations is smaller and genetic progress is slower in breeds other than Holstein, in part because fewer bulls are sampled. A combined national evaluation of data for all breeds and crossbreds may be desirable but would require an extensive programming effort. Animals should receive credit for heterosis when considered as mates for another breed.
Six multiparous Holstein-Friesian cows were offered a total mixed ration based on maize silage in a repeated measure design to evaluate the partition of gross energy (GE) during early to mid lactation. Four measurements were made at 6-week intervals with energy and nitrogen balances carried out in open-circuit respiration chambers over 6 days during lactation weeks 6, 12, 18 and 24. The intakes of total diet dry matter (DM) corrected for volatile losses (VCDM), organic matter (OM) and GE declined significantly (P < 0.02,) as lactation progressed, although apparent digestibility of these fractions was not altered, resulting in a significant (P<0.01) decline in digestible nutrient intake at each stage of lactation. Methane and urine energy losses were not significantly affected, resulting in significantly (P < 0.001) higher amounts of digestible energy (DE) partitioned to methane and urine ns lactation progressed with associated significant reductions in metabolizable energy (ME) intake (MEI) (P < 0.01) and ME as a proportion of DE (P < 0.001) and GE (q) (P < 0.05). With advancing lactation there was a significant (P < 0.001) increase in the amount of ME partitioned to heat (HP/MEI), but no significant change in the amount partitioned to milk and tissue. Individual values for diet metabolizability (ME/GE) at actual (production) levels (qa) (mean 0.625 MJ/MJ) were corrected to an equivalent value at maintenance (qmc) (mean 0.666 MJ/MJ). The overall ME intakes (MJ/day) were: ad libitum, 246, corrected for level of feeding effect, 263, with a predicted ME requirement according to AFRC (1993) (MER93) of 242. Substitution of the calculated qmc into the predictive equations (AFRC, 1993) resulted in a mean maintenance requirement of 57.6 MJ/day (0.464 MJ/kg M0.75/day) whilst the mean value derived from the linear model describing the experimental data was 82.5 MJ/day (0.664 MJ/kg M0.75/day). The mean efficiencies of utilization of ME for milk production derived from AFRC (1993) and the linear regression model were 0.653 MJ/MJ and 0.625 MJ/MJ respectively.
Sixty Holstein/Friesian dairy cows, 28 of high genetic merit and 32 of medium genetic merit, were used in a continuous design, 2 (cow genotypes)×4 (concentrate proportion in diet) factorial experiment. High and medium merit animals had Predicted Transmitting Abilities for milk fat plus protein yield, calculated using 1995 as the base year (PTA95 fat plus protein), of 43·3 kg and 1·0 kg respectively. Concentrate proportions in the diet were 0·37, 0·48, 0·59 and 0·70 of total dry matter (DM), with the remainder of the diet being grass silage. During this milk production trial, 24 of these animals, 12 from each genetic merit, representing three animals from each concentrate treatment, were subject to ration digestibility, and nitrogen and energy utilization studies. In addition, the efficiency of energy utilization during the milk production trial was calculated.
In a series of studies to simulate the ingestion of cold food, the rumen of adult sheep was cooled by 0–400 kJ over 1 h. Ruminal cooling reduced body heat content, increased rate of metabolic heat production and reduced apparent rate of heat loss to the environment. On average, each 100 kJ of cooling reduced heat content by 46 kJ, increased heat production by 20 kJ and reduced heat loss by 70 kJ. Precooling thermal status of the sheep affected the magnitude of the responses to cooling. A 0.1 °C higher precooling mean body temperature decreased the response in metabolic heat production by 6 kJ and increased the reduction in body heat content by 4.6 kJ. The heat production associated with eating reduced the heat loss response to ruminal cooling but did not affect the change in heat content. Well-insulated sheep were less affected by ruminal cooling. Key words: Sheep, rumen, cooling, heat production, temperature
It is well established that the genetic merit of the Holstein-Friesian dairy cow for milk production has increased over the past 20 years. Previous studies have examined the effect of feeding system on indices of body tissue reserves of medium genetic merit Holstein-Friesian dairy cows. The aim of the current study was to examine the weight and concentration of body components in high genetic merit Holstein-Friesian dairy cows, managed on four different grassland-based feeding regimes, using direct measures of body composition. Results indicate that there was no significant effect of different grassland-based feeding regimes on the weight or composition of body components of high genetic merit cows. Therefore, high levels of cow performance can be sustained from very different grassland-based systems of milk production without having a detrimental effect on body tissue reserves.
Heat load impairs the feed intake and milk yield of dairy cows: The higher their milk yield and energy expenditure (EE), the larger the expected effect. Our objective was to examine the efficacy of feeding such cows at night, which avoiding their access to feed for 5 1/2 h during the hot hours of the day, to reduce the heat load upon them in a hot climate. Approximately 120 cows in a herd in a hot region in Israel were allocated to two treatments: day (DFT) or night (NFT) feeding, which differed only in the schedule of feed allocation. The experiment was conducted from May to September 2000 (118 days). The cows were group fed on a total mixed ration, and the daily amounts of feed offered and of orts collected were recorded. The daily group average milk yield was also recorded. Ten cows in each group were selected for individual measurements. The energy expenditure of these cows was estimated once before and three times during the experiment, by monitoring heart rates and measuring oxygen consumption. The rectal temperatures and respiration rates (RR) of these cows were measured in the morning and afternoon on two consecutive days in August. Cows on NFT had lower feed intake but similar milk yield to that of DFT cows, and NFT cows had better milk yield persistence over time. The effects of the temperature–humidity index (THI) on milk yield and intake were similar in the two treatments. The rectal temperature and respiration rate, and the increase in these measures from morning to afternoon hours, did not differ from DFT and NFT cows. The energy expenditure of NFT cows was lower than that of DFT cows, and their efficiency of energy utilization for milk production was higher.
The energy expenditure (EE) of grazing cows and the metabolizable energy (ME) content of the pasture were measured over the course of 3 years under 29 representative treatments of grazing seasons, two different stocking rates, and two periods of confinement. Ten cows were used per treatment. Individual faecal output (FO) was measured for six of the grazing periods, and the metabolizable energy intake (MEI) was calculated from faecal output and in vitro digestibility. EE was estimated from measurements of daily heart rate (HR) and oxygen consumption, calibrated against oxygen consumption per heart beat (O2 pulse). The EE of lactating beef cows on lush pasture in the early spring reached 1260±31 kJ per (kg BW0.75 day); with that of non-lactating cows in the summer decreased to 481±53 kJ per (kg BW0.75 day). The EE and O2 Pulse increased with increasing MEI and ME. The diurnal and annual EE patterns were affected mainly by the herbage quality and intake. A high stocking rate resulted in a decrease in the cows' body condition score (BCS), associated with a reduction in the EE of the cows in confinement. The effects of animal and field conditions on HR, EE, retained energy (RE) and skin temperatures (Tsk) were studied for the grazing periods, and not those from the confinement. Skin temperature was negatively associated with BCS. The HR, EE and retained energy (RE) were highly correlated with MEI (P
IFFERENCES among animals in con- verting feed into body tissue are im- portant in determining net income from beef cattle operations. However, measuring in- dividual feed consumption is costly because of increased equipment and labor require- ments. The heritability of efficiency of feed use and its genetic relationship with other measurable traits need to be examined care- fully before recommendations concerning individual feeding can be made. The problem of measuring efficiency of feed use is dis- cussed in this paper and various measures are evaluated. The genetic and phenotypic variation and covariation among efficiency, gain and feed consumption are examined.
Twenty-four nonlactating and nonpregnant Belgian Blue double-muscled cows, with diverging parities (one to seven), body conditions and body weights (436 to 903 kg), were used to investigate empty body (EB) composition. Direct measurements of EB composition, such as water, fat, protein, ash and energy, were carried out after slaughter. EB weight (EBW) averaged 624.7 kg and consisted of 393.3 kg water, 122.3 kg protein, 84.5 kg fat and 24.6 kg ash and was characterized by an energy content of 6158 MJ. Relationships between body weight (BW), body condition score (BCS), chest girth, dressing percentage, carcass grading score, EBW, rib-cut components and EB composition were determined. Significant regression equations (P<0.001) with a coefficient of determination (R2) of more than 0.9 were obtained between BW or BW and BCS and EB water, EB fat and EB energy. The prediction of EB ash was less accurate (R2<0.75). The relationship could further be improved by inclusion of carcass characteristics and rib-cut components (R2>0.95). Energy contents of EB lipids and protein amounted to 39.3 and 23.2 MJ/kg. EB protein (197 g/kg) was higher in the present double-muscled cows than reported for non-double-muscled animals, while EB fat (126 g/kg) and EB energy (9.5 MJ/kg) were lower. One BCS unit corresponded with 26.7 kg EB fat (P<0.001; R2=0.659). It can be concluded that simple live animal measurements as BW and BCS can be considered as potentially useful predictors of EB composition in double-muscled cows. Theoretical calculations based on the present observed data indicated that body reserves were lower in Belgian Blue double-muscled cows than in most other breeds. Body reserve tissue may be limited in young primiparous suckling cows so that energy restriction may be detrimental for reproductive performance.
The oxygen consumption (VO2) per heart beat (O2 pulse, O2P) can be used for the estimation of energy expenditures as a function of the heart rate (HR) of animals. The magnitude of error of such estimation is derived from the variability of O2P in different environment conditions. Three experiments were carried out to define changes in O2P, attributable to changes in the time of day or in the heat load. In Exp. 1 and 2, calves (n=8) and lambs (n=7), respectively, were measured simultaneously for HR and VO2 five and six times, respectively, during a 24-h period. In Exp. 3, high-yielding dairy cows (n=20) were measured simultaneously for HR and VO2 four times during a 4-month summer season, throughout a wide range of heat load (HL) conditions. The measurements of each animal in all the experiments lasted 10 min. Significant individual variability of HR, VO2 and O2P was observed in all three experiments. The time of day, or the HL, affected HR and tended to affect VO2, but had no effect on O2P in Exp. 1 and 2. On the other hand, both HR and O2P were strongly affected by HL in Exp. 3, and the HL effect on O2P was not linear. We suggest that the difference in response of O2P to HL between milking cows and growing animals could be explained by the higher metabolic rate of the cows. The O2P of growing animals could be used for long-term energy expenditure calculations, whereas the O2P of high-yielding dairy cows should be corrected for the prevailing HL conditions before it can be used for such calculations.
An experiment was conducted in sheep to test the validity of the heart rate method as a tool for determining energy expenditure. A comparison was made between assessments of energy expenditure by this method and the comparative slaughter technique. Animals were kept individually in metabolic cages and were fed ad libitum. One group was fed a high-energy diet, comprised of 75% concentrates and 25% alfalfa hay cubes (C diet) for 84 d. A second group was fed 25% concentrates and 75% of alfalfa hay cubes (R diet) for a 42 d, and then switched to the C diet for 42 d. The third group received the R diet cubes for 84 d. Body composition was determined in four animals at the start of the experiment, and in 12 animals at its termination. The entire experimental period was divided into four sub-periods. For each diet, metabolizability and average heart rate were determined for 3 consecutive days. Individual oxygen consumption was determined by the mask technique and the ratio of oxygen consumption to heart rate, the O2 pulse (O2P), was established for each sub-period. The average ratio of energy expenditure values computed from the product of daily heart rate times O2P to those obtained from the difference between metabolizable energy intake and energy accretion derived from the comparative slaughter technique, was 1.067. We concluded that the monitoring of heart rate combined with a repeatable calibration of individual O2P is a reliable and useful method for determining energy expenditure in ruminants.
The use of heart rate (HR) measurements to estimate energy expenditure (EE) was evaluated, by comparing HR method with energy balance measurements during the reproductive cycle of mature beef cows. Six beef cows, 7- to 10-years-old and 607±29 kg body weight (BW) were used. Intake was measured individually. Organic matter digestibility of the diets was measured, and metabolizable energy (ME) and ME intake (MEI) were calculated from digestibility values. EE was estimated from daily HR measurements and oxygen consumption, calibrated against oxygen consumption per heart beat (O2 pulse). Retained energy (RE) in cows’ BW was calculated on the basis of BW changes, on the assumption that all changes derived from gain or loss of fat tissue. The energy content of the newborn calf and accompanying uterine tissues was calculated from the calf live weight at birth and published data. Milk production was measured on three occasions, as the weight increment of calves following suckling. Milk energy content was measured and the energy retained for milk production was calculated. RE for the entire trial, that is, energy in BW changes, plus the energy in the calf and accompanying uterine tissues, plus the energy in milk, was 4.53±1.09% of MEI. For the 1-year trial of the six cows, the MEI recovery, i.e. the ratio of MEI to (EE+RE), was 1.06±0.026, and the ratio of EE calculated by the difference (MEI−RE) to EE measured by HR was 1.06±0.028, which were not significantly different from the expected value of 1.0. Lactation increased dry matter intake (DMI), MEI, HR and EE. Late pregnancy increased HR and total EE but did not significantly increase EE per kg BW0.75, when BW included the uterine content. Reproductive state did not affect the O2 pulse. It is concluded that: (a) energy expenditure of beef cows during the reproductive cycle can be calculated from HR and O2 pulse; (b) the combination of EE and MEI measurements enables estimation of the feed energy available for production by non-constrained cattle. A significant correlation (P<0.001) was found between the EE, estimated from the HR and O2 pulse, and the MEI; this can be used in the reciprocal calculation to estimate MEI from EE measurement. The suggested method offers significant potential for future use in estimating the energy status of farm animals and in supporting management decisions.
A considerable volume of research in the energy metabolism of dairy cows has been undertaken over the last 2 decades. The purpose of the present review is to reflect on the impact of these studies on the UK metabolisable energy (ME) system, and other net energy (NE) systems, and validate these systems using published calorimetric data. The NE requirement for maintenance (NEm) in the UK ME system is based on the fasting metabolism of cattle, while in other NE systems the NEm was obtained from regression techniques. The NEm values currently used in Europe and North America, which were developed from the data published 30 years ago, have been demonstrated, in recent studies, to be lower than for present dairy cattle. Maintenance metabolic rate can increase with increasing dietary fibre concentration, possibly being due to increasing gut mass and metabolic activity in organs. Grazing cattle require more time and greater physical efforts for eating the same amount of feed as housed animals and thus require extra energy for grazing activity. The NEm of cattle may be a function of body protein mass, rather than total liveweight of the animal. The efficiency of utilisation of ME for lactation (kl) can be derived from regression techniques or calculated by relating milk energy output and energy balance to ME available for production. Dietary fibre concentration has little effect on kl, although it can influence the composition of volatile fatty acids produced in the rumen and consequently shift milk composition and energy partition between milk and body tissue. There is no evidence to show an effect of cow genetic merit on kl, but high genetic merit cows have the ability to partition more energy into milk than medium or low genetic merit cows. The kl has been shown to be higher than the efficiency of utilisation of ME for tissue retention (kg) for dry cows, but ME was utilised with similar efficiency for milk production and concomitant tissue retention. The energy value per unit of liveweight gain or loss should not be fixed as it depends on gut fill and composition of fat, protein and water in the gained or mobilised liveweight. The energy value per mobilised liveweight can also differ with stage of lactation. The above effects are important for dairy cattle feeding and should therefore be incorporated in the future revision of an energy feeding system. The current energy feeding systems used in Australia, the Netherlands, UK and USA have also been validated using calorimetric data of lactating dairy cows published since 1976.
The objectives of this study were accomplished with two experiments in growing Bonsmara bulls (N = 68) (experiment 1), and Simmental crossbred calves (N = 132) (experiment 2). Specific objectives for experiment 1 were to characterize residual feed intake (RFI) in growing bulls, and examine relationships between RFI and performance, fertility, temperament and body composition traits. In experiment 2, the objectives were to examine stocker-phase supplementation effects on feedlot feed conversion ratio (FCR) and RFI and to characterize relationships between these feed efficiency traits, and performance and carcass traits in finishing calves. In both experiments, individual feed intakes and BW were measured. Ultrasound technology was used to measure body composition in experiment 1, while actual carcass measurements taken at harvest were used for experiment 2. Experiment 1 demonstrated that temperament affected ADG and DMI, but not FCR or RFI. Residual feed intake was not phenotypically correlated to scrotal circumference or bull fertility traits. Experiments 1 and 2 demonstrated that RFI was independent of ADG and BW, but that there was a tendency (P < 0.10) for RFI to be phenotypically correlated with 12th rib fat thickness (r = 0.20 and 0.22). However, RFI was not correlated with longissimus muscle area in either experiment. Both experiments demonstrated that low RFI (< 0.5 SD below mean RFI) calves consumed significantly (20 and 22%) less feed and had improved (21%) FCR compared to calves with high RFI (> 0.5 SD above mean RFI). Results from experiment 2 suggest that RFI measured while calves are consuming high-grain diets may be less influenced by previous level of stocker supplementation compared to FCR or residual gain efficiency traits. In summary, RFI was found to be phenotypically independent of growth rate and BW, had no effect on bull fertility or temperament traits, and was less impacted by previous plane of nutrition compared to FCR.
Residual energy intake is defined as the remaining energy from total net energy intake after accounting for all energy uses. Residual energy intake is proposed as a measure of feed efficiency because animal efficiency increases as the proportion of accountable energy intake increases or the residual energy intake decreases. Residual energy intake was estimated for each of 247 Holstein cows, daughters of 127 sires and 226 dams distributed in five herds across the US. Data consisted of daily milk production and net energy intake, biweekly measures of milk components, and BW measures taken at varied intervals throughout a lactation. Average daily net energy intake in a lactation was the dependent variable in a model that contained fixed effects of parity and herd-season subclass; covariates of lactation average daily SCM, metabolic BW, and weight change in a lactation; and random animal effect. From this model, residual energy intake was a sum of animal and residual effects. Partial energy requirements for SCM, maintenance, and weight change estimated for all cows were .54, .15, and 1.52 Mcal/kg, respectively. Heritability estimate for residual energy intake was .016; phenotypic standard deviation was 2.455. The proportion of the phenotypic standard deviation in net energy intake that was due to residual energy was 68%.
A crossbreeding project involving the Holstein and Guernsey breeds was conducted at the Illinois Agricultural Experiment Station from 1949 to 1969. All surviving male calves, 989 of the 1061 born, were sold within 2 or 3 d following birth. All surviving female calves born in the first four generations, 723 of the 788 born, were given an opportunity to conceive and produce milk. Those female calves born in the fifth generation (152 of 166 born) were placed in the University herd or sold to commercial dairy farmers. On a basis of a total of 2015 calves born, crossbreds had a 15.6% greater survival rate to sale or 1 wk of age than purebreds. Of the 778 surviving females born in the first four generations, 18.4% more crossbreds than purebreds calved once, and 24.5% more crossbreds than purebreds calved twice. For weight at 18, 24, 30, 36, and 48 mo of age, crossbreds exceeded purebreds by 5.0, 7.0, 4.4, 3.6, and 5.3%, respectively. Crossbreds were 9.3 d older at calving than purebreds and had an average calving interval than was 9.4 d longer than that for purebreds. For yield of milk, fat, protein, and SNF, crossbreds exceeded purebreds by 8.0, 8.5, 7.5, and 3.0%, respectively. The measures of survival, growth, milk yield, and reproduction were approximately combined into an index of income produced per cow. On a basis of income per cow per lactation, crossbreds exceeded purebreds by 14.9%. On a basis of income produced per cow per year, crossbreds exceeded purebreds by 11.4%.
Early part records for milk yield and feed consumption of 2230 first lactation purebred and crossbred dairy cows were analyzed to evaluate various measures of feed efficiency. Corrected milk yield was estimated by adjusting the second 8 wk of milk yield for differences in weight of TDN consumed during wk 9 to 16, percentage of TDN derived from concentrate, and BW.75. Corrected milk yield is an estimate assuming that cows are the same size and consume the same amount of feed. Hence, it represents an expression of feed efficiency. Net feed efficiency, gross efficiency, corrected milk yield, and wk 9 to 16 milk were analyzed simultaneously. Coefficient of determination for net efficiency (.51) and gross efficiency (.72) were lower than that of milk (.82), whereas corrected milk yield had a coefficient of determination similar to that of milk. Hence, the use of ratios to define feed efficiency was less accurate than using corrected milk yield. Effects of genetic groups, stations, season of freshening, year of freshening, and heterosis were similar for gross efficiency and corrected milk yield, but different from those for milk. Therefore, corrected milk yield performed the same function as feed efficiency with higher accuracy.
Body weight, condition score, deuteriated water dilution space, estimated body lipids and proteins, and calculated energy and protein balances were determined in 24 multiparous Holstein cows at wk 1, 7, 20, and 39 after parturition. Cows received two levels of energy concentrate (high and low groups) from wk 3. The objective was to estimate changes in body composition as affected by stage of lactation, concentrate level, and bST administration or placebo from wk 9 in a 2 x 2 factorial design. Cows from high and low energy groups lost 25 and 35 kg of body lipids and 3.3 and .5 kg of body proteins, respectively, during the first 7 wk of lactation. During the end of the winter period (wk 8 to 20), control and bST-injected cows lost 8.5 and 21.1 kg of body lipids, respectively. During the grazing period (wk 20 to 39), bST-injected cows gained more BW (34 kg), water (36 kg), and estimated proteins (5.8 kg) and lost more condition score (-.2 units) and estimated lipids (-11.5 kg) than controls. Using data from control periods, it was calculated that 1 unit change in body condition score corresponded to changes of 35 to 44 kg in BW (corrected for estimated gut content variation), 21 to 29 kg in body lipids, and 200 to 300 Mcal in body energy. One kilogram of corrected BW change corresponded to a change of 4.3 or 5.5 to 5.9 Mcal in body energy when calculated from cumulative energy balances or body components, respectively.
A simple one-step procedure that eliminates the need to calibrate the O2 analyzer or measure the flow past the animal is described for calibrating an open-flow respirometry system. The technique is particularly useful for situations of high ambient humidity and for large or active animals where a mask is employed to capture expired gases. A measured N2 flow is used to calibrate the system. The equations describing the technique are given, and the accuracy of the method is discussed in detail. The errors associated with the technique are compared with those of more conventional procedures and are usually smaller.
The current energy requirements system used in the United Kingdom for lactating dairy cows utilizes key parameters such as metabolizable energy intake (MEI) at maintenance (MEm), the efficiency of utilization of MEI for 1) maintenance, 2) milk production (kl), 3) growth (kg), and the efficiency of utilization of body stores for milk production (kt). Traditionally, these have been determined using linear regression methods to analyze energy balance data from calorimetry experiments. Many studies have highlighted a number of concerns over current energy feeding systems particularly in relation to these key parameters, and the linear models used for analyzing. Therefore, a database containing 652 dairy cow observations was assembled from calorimetry studies in the United Kingdom. Five functions for analyzing energy balance data were considered: straight line, two diminishing returns functions, (the Mitscherlich and the rectangular hyperbola), and two sigmoidal functions (the logistic and the Gompertz). Meta-analysis of the data was conducted to estimate kg and kt. Values of 0.83 to 0.86 and 0.66 to 0.69 were obtained for kg and kt using all the functions (with standard errors of 0.028 and 0.027), respectively, which were considerably different from previous reports of 0.60 to 0.75 for kg and 0.82 to 0.84 for kt. Using the estimated values of kg and kt, the data were corrected to allow for body tissue changes. Based on the definition of kl as the derivative of the ratio of milk energy derived from MEI to MEI directed towards milk production, MEm and kl were determined. Meta-analysis of the pooled data showed that the average kl ranged from 0.50 to 0.58 and MEm ranged between 0.34 and 0.64 MJ/kg of BW0.75 per day. Although the constrained Mitscherlich fitted the data as good as the straight line, more observations at high energy intakes (above 2.4 MJ/kg of BW0.75 per day) are required to determine conclusively whether milk energy is related to MEI linearly or not.