Daily dry matter intake to sustain body weight of mature, nonlactating, nonpregnant cows1

Heritability of beef cow metabolizable energy for maintenance

Most of the metabolizable energy that a cow uses during a production year is for maintenance; however, less is known about the heritability of maintenance compared to other traits that can be measured directly. Feed intake is a heritable trait in the mature cow and most of the feed consumed is used for maintenance. We hypothesized that maintenance energy was a heritable trait. Individual feed intake was measured for 84 or 85 d on 5 yr old pregnant cows (N = 887) from a pedigreed population of cattle that represent prominent breeds in the United States. Phenotypic mean (± SD) values were 654 ± 68 kg for cow body weight, 0.21 ± 0.24 kg/d for average daily gain, and 175 ± 17 d for midpoint fetal age. Dry matter intake averaged (± SD) 10.84 ± 1.41 kg/d. Metabolizable energy for maintenance was estimated by subtracting the metabolizable energy used for conceptus growth and tissue accretion from metabolizable energy intake. Metabolizable energy for maintenance averaged (± SD) 139 ± 18 ME kcal/d/BW kg0.75 and had a heritability of 0.31 ± 0.11. Cows have a moderate heritability for maintenance suggesting an opportunity for selection.

A mathematical nutrition model adequately predicts beef and dairy cow intake and biological efficiency

The beef cow-calf sector accounts for 70% of feed consumed and greenhouse gases emitted for the beef industry, but there is no straightforward method to measure biological efficiency in grazing conditions. The objective of this study was to evaluate a mathematical nutrition model to estimate the feed intake and biological efficiency of mature beef cows. Data from dams (N = 160) and their second and third progeny (312 pairs) were collected from 1953 through 1980. Individual feed intake was measured at 28-d intervals year-round for dams and during 240-d lactation for progeny. Body weights of progeny were measured at 28-d intervals from birth to weaning, and of dams at parturition and weaning each production cycle. The milk yield of dams was measured at 14-d intervals. Dam metabolizable energy intake (DMEI) and milk energy yield (MEL) of each cow were predicted using the Cattle Value Discovery System beef cow (CVDSbc) model for each parity. Biological efficiency (Mcal/kg) was computed as the ratio of observed or predicted DMEI to observed calf weaning weight (PWW). Pearson correlation coefficients were computed using corr.test function and model evaluation was performed using the epiR function in R software. Average (SD) dam weight, PWW, DMEI, and observed MEL were 527 (86) kg, 291 (47) kg, 9584 (2701) Mcal/production cycle, and 1029 (529) Mcal, respectively. Observed and predicted DMEI (r = 0.93 and 0.91), and observed and predicted MEL (r = 0.58 and 0.59) were positively correlated for progeny 2 and 3, respectively. The CVDSbc model under-predicted DMEI (mean bias [MB] = 1,120 ± 76 Mcal, 11.7% of observed value) and MEL (MB = 30 ± 25 Mcal, 2.9% of observed value). Observed and predicted progeny feed intake were not correlated (r = 0.01, P-value = 0.79). Observed and predicted biological efficiency were positively correlated (r = 0.80 and 0.80, P-value ≤ 0.05) for parity 2 and 3, respectively, and the CVDSbc model under-predicted biological efficiency by 11% (MB = 3.59 ± 0.25 Mcal/kg). The CVDSbc provides reasonable predictions of feed intake and biological efficiency of mature beef cows, but further refinement of the relationship between calf feed intake and milk yield is recommended to improve predictions. Mathematical nutrition models can assist in the discovery of the biological efficiency of mature beef cows.

Grazing beef cows identified as efficient using a nutrition model partition more energy to lactation

Context The efficiency of the cow–calf sector could be enhanced by matching cow biological type to the production environment; however, methods to estimate the biological efficiency of grazing beef cows are not available. Aims This study utilised a mathematical nutrition model for ranking beef cows for estimated biological efficiency, determining energetic efficiency and evaluate relationships with other production traits. Methods Cow live weight, calf birth and weaning weight, calf birth and weaning date, and forage nutritive value of hay and pasture were collected for 69 Brangus crossbred beef cows over a complete production cycle. The Cattle Value Discovery System for Beef Cow (CVDSbc) model was used to compute metabolisable energy required (MER) for the cow, and energy efficiency index (EEI) was computed as the ratio of MER to calf weaning weight. Pearson correlation coefficients were computed among performance traits. During late lactation and gestation, low (n=8) and high (n=8) EEI cows were individually fed ad libitum for 44 and 32 days, respectively, then fed 0.5× the estimated metabolisable energy required for maintenance for 7 days (gestation experiment only). Apparent nutrient digestibility, heat production, and milk yield were measured. Key results EEI was strongly negatively correlated (P<0.05) with model predicted peak milk (−0.62) and calf weaning weight (−0.65), but moderately correlated (P<0.05) with cow live weight (0.46). Dry matter intake was not different (P>0.75) between low and high EEI cows even though low EEI cows weighed less (P<0.05) during late lactation and gestation experiments. Low EEI cows tended to have greater efficiency of metabolisable energy use for maintenance and gain (P<0.10), and EEI was negatively correlated (P<0.05) with the efficiency of metabolisable energy use for maintenance (−0.56) and gain (−0.57). Conclusion The CVDSbc model identified cows that weaned heavier calves due to greater dry matter intake of cows relative to live weight allowing more energy apportioned towards lactation, and more efficient use of metabolisable energy for maintenance and gain. Implications Energy efficiency index might provide a logical assessment of biological efficiency of beef cows in grazing production systems.

Maternal body composition in seedstock herds. 1. Grazing management strategy influences perspectives on optimal balance of production traits and maternal productivity

Seedstock breeders’ perspectives on topics associated with maternal productivity in beef cattle were investigated through the use of qualitative in-depth semi-structured interviews. Given the complexity of maternal productivity, it is possible that some issues may not be fully captured by recording performance and data analysis. This paper discusses theory emerging from content analysis of interview data on management and genetic factors affecting maternal productivity as detailed by seedstock breeders in southern Australia. Overall, 24 interviews were conducted as part of an intensive field-work component with seedstock breeders involved with the Cooperative Research Centre for Beef Genetic Technologies’ Maternal Productivity Project. Qualitative content analysis of interview data revealed a considerable divergence in attitudes to cow management with regards to grazing management, body condition fluctuation and the utilisation of body fat reserves. Specifically, production systems diverged on the basis of animal management characterised by either ‘controlled’ or ‘variable input’ feeding strategies. Variation in management approach was associated with different perspectives on the perceived importance of selecting for production traits including growth, beef yield and milk compared with selection for perceived resilience traits including increased subcutaneous fat. The results demonstrated that among seedstock breeders targeting similar end markets, substantial variation in animal selection and management exists and this requires further characterisation to ensure breeding programs and animal management are optimal.

Maternal body composition in seedstock herds. 5. Individual-trait selection direction aligns with breeder perspectives on maternal productivity

The present paper quantifies the variation in selection direction and genetic merit for the 10 Angus seedstock herds that contributed the majority of the data to the industry herd component of the Beef CRC Maternal Productivity Project. Differences in multi-trait selection direction for 17 BREEDPLAN estimated breeding values (EBVs) ranged between 16 and 63 degrees. Important differences among herds for selection direction for individual EBVs were identified. Specifically, some herds had been selecting to increase rib-fat and rump-fat EBV, while others were decreasing them. On the basis of a principal component analysis, 78% of the between herd difference in genetic merit as assessed by 17 EBVs was accounted for by two principal components. For 2000-born calves, the first principal component accounted for 50% of the genetic variation between herds and was most closely associated with days to calving EBV. Of the genetic merit for 2009-born calves, the first principal component accounted for 49% of the between herd variation and had the strongest weightings with BREEDPLAN rib-fat and rump-fat EBVs. The second principal component accounted for 29% of the variation and was most strongly related with BREEDPLAN EBVs for traits gestation length, milk and eye muscle area and 200-, 400- and 600-day weight. The variation at 2009 is consistent with outcomes from qualitative research that hypothesised that the main differences in genetic merit among herds are associated with rib-fat and rump-fat EBVs, but there were also differences in selection emphasis for weight traits. Despite differences in genetic merit among herds being generally small, they will manifest themselves in different productivity outcomes depending on the management system. Seedstock breeders and bull buyers should be aware of this and target their animal selection accordingly.

Toward a theory of energetically optimal body size in growing animals

Our objective was to formulate a general and useful model of the energy economy of the growing animal. We developed a theory that the respiratory energy per unit of size reaches a minimum at a particular point, when the marginal respiratory heat production rate is equal to the average rate. This occurs at what we defined as the energetically optimal size for the animal. The relationship between heat production rate and size was found to be well described by a cubic function in which heat production rate accelerates as the animal approaches and then exceeds its optimal size. Reanalysis of energetics data from the literature often detected cubic curvature in the relationship between heat production rate and body size of fish, rats, chickens, goats, sheep, swine, cattle, and horses. This finding was consistent with the theory for 13 of 17 data sets. The bias-corrected Akaike information criterion indicated that the cubic equation modeled the influence of the size of a growing animal on its heat production rate better than a power function for 11 of 17 data sets. Changes in the sizes and specific heat production rates of metabolically active internal organs, and body composition and tissue turnover rates were found to explain notable portions of the expected increase in heat production rate as animals approached and then exceeded their energetically optimum size. Accelerating maintenance costs in this region decrease net energy available for productive functions. Energetically and economically optimum size criteria were also compared.

Pyrosequencing reveals diverse fecal microbiota in Simmental calves during early development

From birth to the time after weaning the gastrointestinal microbiota of calves must develop into a stable, autochthonous community accompanied by pivotal changes of anatomy and physiology of the gastrointestinal tract. The aim of this pilot study was to examine the fecal microbiota of six Simmental dairy calves to investigate time-dependent dynamics of the microbial community. Calves were followed up from birth until after weaning according to characteristic timepoints during physiological development of the gastrointestinal tract. Pyrosequencing of 16S rRNA gene amplicons from 35 samples yielded 253,528 reads clustering into 5410 operational taxonomic units based on 0.03 16S rRNA distance. Operational taxonomic units were assigned to 296 genera and 17 phyla with Bacteroidetes, Firmicutes, and Proteobacteria being most abundant. An age-dependent increasing diversity and species richness was observed. Highest similarities between fecal microbial communities were found around weaning compared with timepoints from birth to the middle of the milk feeding period. Principal coordinate analysis revealed a high variance particularly in samples taken at the middle of the milk feeding period (at the age of approximately 40 days) compared to earlier timepoints, confirming a unique individual development of the fecal microbiota of each calf. This study provides first deep insights into the composition of the fecal microbiota of Simmental dairy calves and might be a basis for future more detailed studies.

The effects of metabolizable energy intake on body fat depots of adult Pelibuey ewes fed roughage diets under tropical conditions

The objective of this work was to evaluate the effect of metabolizable energy intake (MEI) on changes in fat depots of adult Pelibuey ewes fed roughage diets under tropical conditions. Eighteen 3-year-old Pelibuey ewes with similar body weight (BW) of 37.6 ± 4.0 kg and body condition score (BCS) of 2.5 ± 0.20 were randomly assigned to three groups of six ewes each in a completely randomized design. Ewes were housed in metabolic crates and fed three levels of MEI: low (L), medium (M), and high (H) for 65 days to achieve different BW and BCS. At the end of the experiment, the ewes were slaughtered. Data recorded at slaughter were: weights of viscera and carcass. Internal fat (IF, internal adipose tissue) was dissected, weighed, and grouped as pelvic (around kidneys and pelvic region), omental, and mesenteric regions. Carcass was split at the dorsal midline in two equal halves, weighed, and chilled at 6°C during 24 h. After refrigeration, the left half of the carcass was completely dissected into subcutaneous and intermuscular fat (carcass fat). Dissected carcass fat (CF) of the left carcass was adjusted as whole carcass. At low levels of MEI, proportion of IF and CF was approximately 50%; however, as the MEI was increased, the proportion of IF was increased up to 57% and 60% for M and H, respectively. Omental and pelvic fat depots were those which increased in a larger proportion with respect to the mesenteric fat depot. Regression equations between the weight of each body fat depot and BW had a coefficient of determination (r (2)) that ranged between 0.37 for mesenteric fat and 0.87 for CF. The regression with BCS had a r (2) that ranged between 0.57 for mesenteric and 0.71 for TBF. BW was the best predictor for TBF, CF, omental fat, and pelvic fat; whereas, BCS was better than BW in predicting IF and mesenteric fat. Inclusion of both BW and BCS in multiple regressions improved the prediction for all fat depots, except for pelvic fat, which was best estimated by BCS alone. The greater slope of the regression for the pelvic fat depot equation, relative to TBF (1.40), EBW (4.02), and BCS (2.36), suggested that pelvic fat has a greater capacity to accumulate and mobilize fat. These results indicated that adult Pelibuey ewes seem to store a considerable proportion of absorbed energy in the IF depots rather than in the carcass.

Body composition and estrous cyclicity responses of heifers of distinct body conditions to energy restriction and repletion

Twenty Simmental x Angus, half-sibling, postpubertal heifers (initial BW of 443 +/- 9 kg) were allotted randomly to 2 treatments to evaluate if initial BCS affects how heifers respond to energy restriction and repletion. Dependent variables of interest were changes in BW, BCS, and reproductive status [determined by concentrations of serum progesterone (P(4))]. Empty body composition (EBC) was calculated using equations based on BCS. During a preliminary feeding period, diets were formulated so that each heifer in the designated treatment would reach a BCS of 5 (moderate condition; MOD) or a BCS of 7 (heavy condition; FAT). Once each heifer had reached the desired BCS, diets were formulated to supply 30% of NE(m) requirements until each heifer became anestrous (serum concentrations of P(4) < 1 ng/mL; restriction period). After anestrus, heifers were fed a high energy diet (1.43 Mcal/kg of DM) until estrous cycles resumed (serum concentrations of P(4) > 1 ng/mL; repletion period). Body weight, BCS, and EBC were determined on d 1 of each period, on d 43 of restriction, and d 44 of repletion, and when heifers were confirmed to have resumed estrous cycles (2 normal estrous cycles determined by P(4) > 1 ng/mL). Regression of BCS on BW determined individual BCS at anestrus and estrus. After 43 d of restriction, FAT condition heifers were heavier (P < 0.001), had greater BCS (P < 0.001), and had a greater proportion of empty body fat (P < 0.001). Heifers in FAT condition remained cyclic longer (P < 0.001) than those in MOD condition (148 vs. 61 d). In contrast, at the onset of anestrus, BW (P = 0.15), BCS (P = 0.54), and empty body fat were similar (P = 0.54) between treatments. At 44 d of repletion, BW (P = 0.46), BCS (P = 0.41), and empty body fat (P = 0.41) were similar between treatments. Heifers in both treatments recommenced estrous activity after similar (P = 0.43) number of days (54 d) of energy repletion, but near onset of estrous cycles, heifers in FAT condition were heavier (P = 0.002) and had greater BCS (P = 0.03) and empty body fat (P = 0.01) than those in MOD condition. Initial BCS influenced days to anestrus, but not BCS or EBC at onset of anestrus. Initial BCS had no effect on days to recommencement of estrous cycles, but did influence the degree of fatness required to resume estrous cycles.

Cow/calf preweaning efficiency of Nellore and Bos taurus x Bos indicus crosses

The objectives of this study were to determine if percentage Bos taurus (0 or 50%) of the cow had an effect on ME requirements and milk production, and to compare cow/calf efficiency among 3 mating systems. Metabolizable energy requirements were estimated during a feeding trial that encompassed a gestation and lactation feeding trial for each of 2 groups of cows. Cows were 0 or 50% Bos taurus (100 or 50% Nellore) breed type: Nellore cows (NL; n = 10) mated to Nellore bulls, NL cows (n = 9) mated to Angus bulls, Angus x Nellore (ANL; n = 10) and Simmental x Nellore (SNL; n = 10) cows mated to Canchim (5/8 Charolais 3/8 Zebu) bulls. Cows were individually fed a total mixed diet that contained 11.3% CP and 2.23 Mcal of ME/kg of DM. At 14-d intervals, cows and calves were weighed and the amount of DM was adjusted to keep shrunk BW and BCS of cows constant. Beginning at 38 d of age, corn silage was available to calves ad libitum. Milk production at 42, 98, 126, and 180 d postpartum was measured using the weigh-suckle-weigh technique. At 190 d of age, calves were slaughtered and body composition estimated using 9-10-11th-rib section to obtain energy deposition. Regression of BW change on daily ME intake (MEI) was used to estimate MEI at zero BW change. Increase in percentage Bos taurus had a significant effect on daily ME requirements (Mcal/d) during pregnancy (P < 0.01) and lactation (P < 0.01). Percentage Bos taurus had a positive linear effect on maintenance requirements of pregnant (P = 0.07) and lactating (P < 0.01) cows; during pregnancy, the ME requirements were 91 and 86% of those in lactation (131 +/- 3.5 vs. 145 +/- 3.4 Mcal x kg(-0.75) x d(-1)) for the 0 and 50% B. taurus groups, respectively. The 50% B. taurus cows, ANL and SNL, suckling crossbred calves had greater total MEI (4,319 +/- 61 Mcal; P < 0.01) than 0% B. taurus cows suckling NL (3,484 +/- 86 Mcal) or ANL calves (3,600 +/- 91 Mcal). The 0% B. taurus cows suckling ANL calves were more efficient (45.3 +/- 1.6 g/Mcal; P = 0.03) than straightbred NL (35.1 +/- 1.5 g/Mcal) and ANL or SNL pairs (41.0 +/- 1.0 g/Mcal). Under the conditions of this study, crossbreeding improved cow/ calf efficiency and showed an advantage for cows that have lower energy requirements.