Assessment of Equations to Predict Body Weight and Chemical Composition in Growing/Finishing Cattle and Effects of Publication Year, Sex, and Breed Type on the Deviation from Observed Values.

Body weight and chemical composition are important aspects of beef cattle nutrition and management; however, existing equations estimating relationships among empty body and carcass chemical components were developed over 40 years ago using different cattle genetics and production systems. The objective of this analysis was to evaluate existing equations in predicting empty body and carcass chemical composition and determine the effect of sex, breed type, and publication year. A dataset was developed from published literature that contained 388 treatment means from 46 studies published between 1970 and 2020. Two equations relating shrunk body weight (SBW) to empty body weight (EBW), and 8 equations relating EBW and hot carcass weight (HCW) were found in the literature and evaluated using the developed dataset. Three sets of equations relating empty body chemical components, 4 sets of equations relating carcass chemical components, and 2 sets of equations relating carcass with empty body chemical components were found in the literature and evaluated using the dataset. Precision and accuracy of the equations were evaluated by simple linear regression of observed on predicted values, mean bias (MB), and concordance correlation coefficient (CCC). Additionally, the fixed effects of publication year, sex, and breed type on the deviation from observed values were evaluated using a general linear model. Both equations relating SBW to EBW and all equations relating EBW to HCW had high precision, but accuracy varied from -3.22 to -0.11% and -9.35 to -3.73% MB, respectively, and all the equations were affected by sex and breed type with 8 out of the 10 equations affected by publication year. For prediction of empty body chemical composition assuming empty body water is known, the 3 sets of equations varied in precision for protein (0.18 to 0.46), but not for fat (0.88 to 0.96) or ash (0.06 to 0.13) based on CCC, although the precision of prediction of protein and ash were poor. Accuracy of the 3 sets of equations varied for predicting empty body fat, protein, and ash with MB of -19.73 to -3.81, 1.67 to 15.91, and -0.16 to 15.75%, respectively. All 3 sets of equations were affected by publication year and breed type for predicting empty body fat, protein, and ash, and by sex for ash. For prediction of carcass chemical components assuming carcass water is known, the precision was similar among the 4 sets of equations for predicting fat (0.92 to 0.95), protein (0.34 to 0.40), and ash (-0.02 to -0.01) based on CCC, although precision was poor for protein and ash, but accuracy varied for prediction of carcass fat, protein and ash with MB of -11.20 to -2.52, 2.72 to 8.92, and -4.66 to 20.12%, respectively. Publication year and breed type affected the prediction of carcass fat and protein, and publication year, sex, and breed type affected the prediction of carcass ash for all 4 sets of equations. The precision of predicting empty body chemical components assuming carcass chemical components are known was high for water (0.96 and 0.98), fat (0.97 and 0.98), protein (0.97 and 0.97), and ash (0.98 and 0.96) and similar between the 2 sets of equations based on CCC. The accuracy of predicting empty body water (-1.68 and -0.33%), fat (6.38 and 2.70%), protein (0.85 and -0.54%), and ash (-0.65 and -4.54%) was moderate to high, but differed between sets of equations for fat and ash. Publication year influenced the prediction of empty body water for both sets of equations and ash for one of the equations, whereas, breed type influenced the prediction of water, protein, and ash, but not fat for both equations. Overall, existing equations may have major limitations to predicting empty body protein and ash unless carcass protein and ash are known. Additionally, all the equations were affected by some combination of publication year, sex, and breed type for one or more chemical components. Thus, a more robust set of equations should be developed to account for sex, breed type, and more recent cattle genetics and management systems.

Evaluation of predictive models to determine total morbidity outcome of feedlot cattle based on cohort-level feed delivery data during the first 15 days on feed.

Changes in feeding behavior and intake have been used to predict the onset of bovine respiratory disease in individual animals but have not been applied to cohort-level data. Correctly identifying high morbidity cohorts of cattle early in the feeding period could facilitate the administration of interventions to improve health and economic outcomes. The study objective was to determine the ability of feed delivery data from the first 15 days of feed to predict total feeding period morbidity. Data consisted of 518 cohorts (10 feedlots, 56,796 animals) of cattle of varying sex, age, arrival weight, and arrival time of year over a 2-year period. Overall cohort-level morbidity was classified into high (≥15% total morbidity) or low categories with 18.5% of cohorts having high morbidity. Five predictive models (advanced perceptron, decision forest, logistic regression, neural network, and boosted decision tree) were created to predict overall morbidity given cattle characteristics at arrival and feeding characteristics from the first 15 days. The dataset was split into training and testing subsets (75% and 25% of original, respectively), stratified by the outcome of interest. Predictive models were generated in Microsoft Azure using the training set and overall predictive performance was evaluated using the testing set. Performance in the testing set (n = 130) was measured based on final accuracy, sensitivity (Sn, the ability to accurately detect high morbidity cohorts), and specificity (Sp, the ability to accurately detect low morbidity cohorts). The decision forest had the highest Sp (97%) with the greatest ability to accurately identify low morbidity lots (103 of 106 identified correctly), but this model had low Sn (33%). The logistic regression and neural network had similar Sn (both 63%) and Sp (69% and 72%, respectively) with the best ability to correctly identify high morbidity cohorts (15 of 24 correctly identified). Predictor variables with the greatest importance in the predictive models included percent change in feed delivery between days and 4-day moving averages. The most frequent variable with a high level of importance among models was the percent change in feed delivered from d 2 to 3 after arrival. In conclusion, feed delivery data during the first 15 days on feed was a significant predictor of total cohort-level morbidity over the entire feeding period with changes in feed delivery providing important information.

Effect of rumen-protected methionine supplementation to beef cows during the periconception period on performance of cows, calves, and subsequent offspring.

Maternal nutrition affects the development of the fetus and postnatal performance of the calf. Methionine may play a critical role in developmental programming and is likely deficient in beef cows fed low-quality forage. The objective of this study was to determine the effect of metabolizable methionine supply to lactating beef cows during the periconception period on performance of cows, calves, and subsequent offspring. This project involved two consecutive production cycles commencing at calving in which dietary treatments were fed to cows during the periconception period along with measurements on cows and initial calves in Production Cycle 1, and measurements on subsequent calves in Production Cycle 2. Brangus-Angus crossbred lactating beef cows (N = 108; age = 6.4 (2.8) year) were stratified by previous calving date and assigned to one of three supplements: (1) control, molasses plus urea at 2.72 kg/day as fed, (2) fishmeal, 2.27 kg/day molasses plus urea plus 0.33 kg/day as fed of fishmeal, and (3) methionine, 2.72 kg/day of molasses plus urea plus 9.5 g/day of 2-hydroxy-4-(methylthio)-butanoic acid. Cows were fed supplements and low-quality limpograss (Hemarthria altissima) hay while grazing dormant bahiagrass (Paspalum notatum Flüggé) pastures during the 115-day periconception period from December 2014 to April 2015 in Production Cycle 1 only. Body weight change and milk yield of cows were measured during the periconception period in Production Cycle 1. Body weight of calves was measured at birth and weaning in both production cycles. Following weaning in Production Cycle 2, eight subsequent steer calves per treatment were individually housed for a 42-day metabolism experiment. Treatment did not affect (P > 0.10) BW change of cows, but cows fed methionine tended (P = 0.09) to produce more energy-corrected milk than control and fishmeal. Treatment did not affect (P > 0.10) 205-day adjusted weaning weight of calves in either production cycle. During the metabolism experiment, subsequent calves from dams fed fishmeal and methionine gained faster (P < 0.05) and had greater (P < 0.05) gain:feed than control calves. Methionine calves tended (P = 0.06) to have greater apparent total tract NDF and ADF digestibility and lesser (P < 0.05) blood glucose concentration than control and fishmeal calves. These data indicate that maternal methionine supply during the periconception period plays an important role in programming future performance of the offspring.

Life cycle efficiency of beef production: IX. Relationship between residual feed intake of heifers and cow efficiency ratios based on harvest, carcass, and wholesale cut weight outputs.

Data were collected from 1953 through 1980 from identical and fraternal twin beef and dairy females born in 1953, 1954, 1959, 1964, and 1969, from crossbred females born as singles in 1974, and their progeny. Numbers of dams that weaned at least one calf and were included in the first analysis were 37, 45, and 56 in the 1964, 1969, and 1974 data sets, respectively. Respective numbers of dams that weaned three calves and were included in a second analysis were 6, 8, 8, 22, 33, and 33 in the 1953, 1954, 1959, 1964, 1969, and 1974 experiments. Individual feed consumption was measured at 28-d intervals from the time females were placed on the experiment at 240 d of age until three calves were weaned or the dams had reached 5 yr of age. Residual feed intake (RFI) and residual BW gain (RG) of heifers that subsequently became dams were determined based on ADG and DMI from 240 d of age to first calving. Various measures of cow efficiency were calculated on either a life cycle or actual lifetime basis using ratios of progeny and dam weight outputs to progeny and dam feed inputs. The correlation between RFI and DMI was large and positive (r = 0.67; P < 0.0001), and RG was highly correlated with ADG (r = 0.75; P < 0.0001). Correlations of RFI with cow efficiency ratios that included harvest weight, carcass weight, or weight of trimmed wholesale cuts as measures of output ranged from -0.05 (P > 0.10) to -0.17 (P < 0.10), indicating that heifers with better (i.e., more negative) RFI values tended to become slightly more efficient cows. Correlations of RG with life cycle and actual lifetime cow efficiency ratios ranged from 0.08 (P > 0.10) to 0.23 (P < 0.05), demonstrating that heifers with better (i.e., more positive) values for RG were somewhat more efficient as cows. The correlations were stronger when cow salvage value was included in the measures of cow efficiency. Correlations of DMI and mid-test metabolic BW (MMW) with life cycle cow efficiency ratios that did not include cow salvage value as output ranged from -0.15 (P < 0.10) to -0.22 (P < 0.01). Correlations of DMI and MMW with actual lifetime cow efficiency ratios varied from -0.20 (P < 0.05) to -0.36 (P < 0.001). Therefore, smaller heifers that consumed less feed had superior cow efficiency ratios. Correlations of RFI with carcass grade, backfat thickness, marbling score, and kidney fat of progeny indicated that heifers with superior RFI would tend to produce leaner offspring.

Exposure to lipopolysaccharide in utero alters the postnatal metabolic response in heifers.

This study was designed to determine the effect of prenatal lipopolysaccharide (LPS) exposure on the postnatal metabolic response to an LPS challenge in beef heifers. Pregnant, crossbred cows ( = 50) were assigned to a prenatal immune stimulation (PIS; = 25; administered 0.1 µg/kg BW LPS subcutaneously 233 ± 15d of gestation) or saline treatment group (Control; = 25). Birth and weaning BW of calves were collected. There was not (> 0.05) a treatment × gender interaction for birth weight or 205-d adjusted weaning BW. Treatment did not affect (> 0.05) birth BW, but steers and heifers of PIS cows had greater ( < 0.02) 205-d adjusted weaning BW than offspring from Control cows. From the 2 prenatal treatment groups, heifer calves ( = 12 PIS, 11 Control) were identified at weaning (238 ± 15 d of age) to subsequently receive an LPS challenge. On d 0, heifers were fitted with indwelling jugular catheters and were moved into individual pens. On d 1, heifers (fed at 0600 h) were challenged i.v. with LPS (0.5 µg/kg BW) at 0 h (1000 h). Blood samples were collected at 30-min intervals from -2 to 8 h and again at 24 h relative to the LPS challenge. There was a treatment × time interaction ( < 0.01) for cortisol; PIS heifers had greater cortisol from 4 to 6.5 h post-LPS challenge ( < 0.001). There was a treatment × time interaction ( = 0.04) for serum glucose such that glucose was greater ( = 0.01) in PIS than Control heifers at 0.5 h, but was greater in Control than PIS heifers at 2, 4.5, and 7 h post-LPS challenge. This resulted in overall time ( < 0.01) and treatment ( < 0.01) effects such that Control heifers had greater glucose concentrations than PIS heifers. There was a tendency ( = 0.10) for a treatment × time interaction for serum NEFA, such that NEFA was greater in Control than PIS heifers at -2, -1.5, and 7 h relative to the LPS challenge ( ≤ 0.02). Also, there were time ( < 0.01) and treatment effects ( < 0.01) for NEFA with Control heifers having greater NEFA than PIS heifers. Serum BUN was affected by a treatment × time interaction ( < 0.01). Concentrations of BUN were greater in PIS heifers from -1.5 to -1 h, 1 to 2 h, at 4 h, and from 5 to 24 h relative to the LPS challenge. These results demonstrate postnatal growth and the metabolic responses of weaned beef calves can be significantly altered with a single exposure to LPS in utero.

Life cycle efficiency of beef production: VIII. Relationship between residual feed intake of heifers and subsequent cow efficiency ratios.

Data were collected from 1953 through 1980 from identical and fraternal twin beef and dairy females born in 1953, 1954, 1959, 1964, and 1969, and from crossbred females born as singles in 1974, and their progeny. Numbers of dams that weaned at least 1 calf and were included in the first analysis were 37, 45, and 56 in the 1964, 1969, and 1974 data sets, respectively. Respective numbers of dams that weaned 3 calves and were included in a second analysis were 6, 8, 8, 22, 33, and 33 in the 1953, 1954, 1959, 1964, 1969, and 1974 experiments. Individual feed consumption was measured at 28-d intervals from the time females were placed on the experiment until 3 calves were weaned or the dams had reached 5 yr of age. Residual feed intake (RFI) and residual gain (RG) of the heifers that subsequently became the dams in this study were determined based on ADG and DMI from 240 d of age to first calving. Various measures of cow efficiency were calculated on either a life cycle or actual lifetime basis using ratios of progeny and dam weight outputs to progeny and dam feed inputs. Residual feed intake was phenotypically independent of ADG and metabolic midweight (MMW), whereas the correlation between RFI and DMI was positive and highly significant ( = 0.67; < 0.0001). Residual gain was highly correlated with ADG ( = 0.75; < 0.0001) and had near 0 correlations with DMI and MMW. Correlations indicated that heifers that ate less and had smaller metabolic midweights from 240 d of age to first calving had superior efficiency ratios as cows. Residual feed intake was not significantly correlated with age at puberty, age at calving, or milk production. Results of this study do not indicate any serious antagonisms of postweaning heifer RFI with subsequent cow and progeny performance traits or with life cycle or actual lifetime cow efficiency. In addition, selection for increased RG would result in earlier ages at calving, but would also tend to result in taller and heavier cows.

Coordinated gene expression between skeletal muscle and intramuscular adipose tissue in growing beef cattle.

Previous research indicates that metabolism and fiber type of skeletal muscle is related to intramuscular lipid content. It is hypothesized that changes in skeletal muscle gene expression influence adipose tissue development. The objective of this study was to determine differences in the metabolism and intercellular signaling of skeletal muscle fibers within the same muscle group that could be responsible for the initiation of intramuscular adipose tissue development and differentiation. Longissimus dorsi muscle samples were collected from steers ( = 12; 385 d of age; 378 kg BW) grazing wheat pasture. Longissimus muscle samples were dissected under magnification and sorted into 3 categories based on visual stage of adipose tissue development: immature intramuscular adipose tissue (MM), intermediate intramuscular adipose tissue (ME), and mature intramuscular adipose tissue (MA). Additionally, muscle fibers lying adjacent to each intramuscular adipose tissue (IM) category and those not associated with IM tissue were collected and stored separately. Quantitative real-time PCR was used to determine relative fold change in genes involved in metabolism, angiogenesis, formation of extracellular matrix, and intercellular signaling pathways in both LM and IM samples. Gene expression data were analyzed using a GLM that included the fixed effect of tissue. Pearson correlation coefficients were also computed between gene expression in LM and IM tissue samples that were at the same stage of development. and γ mRNA expression were 3.56- and 1.97-fold greater ( < 0.05) in ME and MA IM compared with MM IM whereas mRNA expression was 1.43-fold less ( < 0.01) in MA IM compared with MM IM, indicating successful separation into different development categories. Genes associated with metabolism and angiogenesis in LM tissue showed no differences among stages of development. Myostatin expression did not change in LM tissue; however, expression of and mRNA decreased ( < 0.01) as IM matured. and mRNA expression were 2.5- and 1.32-fold greater in LM associated with MM IM than in LM associated with ME IM. Angiogenic growth factors in MM IM tissue had a strong positive correlation ( ≥ 0.69) with angiogenic growth factors in LM associated with MM IM; however, no correlation was observed in ME or MA IM. These data indicate a coordinated effort between LM and IM in early stages of IM development.

Effect of rate of weight gain of steers during the stocker phase. IV. Rumen fermentation characteristics and expression of genes involved in substrate utilization for fatty acid synthesis in adipose tissues of growing-finishing beef cattle.

The objective of this study was to determine the impact of stocker production systems differing in growth rate on rumen fermentation characteristics and utilization of substrates for fatty acid synthesis in intramuscular (IM), subcutaneous (SC), and perirenal (PR) adipose tissues. Angus steers were assigned to 4 stocker cattle production systems in 2 consecutive years: 1) 1.0 kg/d of 40% CP cottonseed meal­based supplement while grazing dormant native range (CON), 2) ground corn/soybean meal­based supplement while grazing dormant native range fed at 1% of BW (CORN), 3) grazing wheat pasture at a high stocking rate to achieve a low rate of BW gain (LGWP), and 4) grazing wheat pasture at a low stocking rate for a high rate of BW gain (HGWP). Eight ruminally cannulated steers were used to determine rumen fermentation characteristics. Steers were harvested during the stocker phase at similar age (different carcass weight) in Exp. 1 (3 steers/treatment) or at similar carcass weight in Exp. 2 (4 steers/treatment). Adipose tissues were analyzed for mRNA expression of genes involved in glucose (solute carrier family 2, member 4 [GLUT4], glucose-6-phosphate dehydrogenase [G6PDH], phosphofructokinase, muscle [PFKM], and pyruvate kinase 2, muscle [PK2]), lactate (lactate dehydrogenase B [LDHB]), and acetate (acetyl-CoA synthetase, cytosol [ACSS2]) utilization for fatty acid synthesis. The acetate:propionate ratio was least (P < 0.05) for HGWP steers, intermediate for CORN and LGWP steers, and greatest for CON steers. At similar age, LGWP and HGWP steers tended (F-test; P < 0.15) to have greater (P < 0.10) G6PDH and ACSS2 mRNA expression than CON and CORN steers in SC and PR but not IM adipose tissue. Expression of PFKM and PK2 mRNA tended (F-test; P < 0.15) to be greater (P < 0.10) in HGWP than CON and LGWP steers in IM but not SC or PR adipose tissue. At similar HCW, expression of GLUT4 and G6PDH mRNA were greater (P < 0.10) in SC adipose tissue of LGWP and HGWP steers compared with CON and CORN steers but not in IM and PR adipose tissue. Expression of LDHB mRNA was lesser (P < 0.10) in SC adipose tissue but greater (P < 0.10) in PR adipose tissue of LGWP and HGWP steers compared with CON and CORN steers. These results indicate a shift toward glucose utilization in SC adipose tissue but a shift towards lactate utilization in PR adipose tissue. These results suggest that diet and changes in VFA profile can influence substrates utilized for fatty acid synthesis, but diet has a greater effect in SC than IM adipose tissue.

Relationships between residual feed intake and hepatic mitochondrial function in growing beef cattle.

The objective of this study was to evaluate the relationship between hepatic mitochondrial function and residual feed intake (RFI) in growing beef cattle. In Trial 1, RFI was measured in 29 Angus heifers (initial BW = 258.0 ± 24.9 kg) from divergent IGF-I selection lines created at the Eastern Agricultural Research Station (The Ohio State University) fed a grain-based diet (calculated ME = 2.85 Mcal/kg DM). In Trial 2, RFI was measured in 119 Santa Gertrudis steers (initial BW = 308.4 ± 28.1 kg) fed a roughage-based diet (calculated ME = 2.21 Mcal/kg DM). At the end of the RFI measurement period, cattle in Trial 1 (n = 7 low RFI and n = 7 high RFI) and in Trial 2 (n = 6 low RFI and n = 8 high RFI) with measures of RFI exceeding 0.5 (Trial 1) or 1.0 (Trial 2) SD from the mean RFI were selected to measure mitochondrial function. Overall ADG, DMI, and RFI were 1.19 ± 0.15, 9.31 ± 1.12, and 0.00 ± 0.63 kg/d and 0.83 ± 0.16, 9.48 ± 1.00, and 0.00 ± 0.86 kg/d in Trial 1 and 2, respectively. Cattle with low RFI consumed 13 and 24% less (P < 0.05) DM and had 14 and 56% greater (P < 0.05) G:F than cattle with high RFI in Trial 1 and 2, respectively, even though ADG and BW were similar (P > 0.10). In Trial 1, cattle with low RFI tended (P = 0.06) to have greater state 3 respiration rates than cattle with high RFI, but state 3 respiration rates were similar (P > 0.10) between cattle with low and high RFI in Trial 2. In both trials, cattle with low RFI had greater (P < 0.05) acceptor control ratios than their high RFI counterparts. The respiratory control ratio tended (P = 0.09) to be greater for cattle with low RFI compared with high RFI cattle in Trial 1, but no difference (P > 0.10) was observed in Trial 2. Proton-leak kinetics were similar (P > 0.05) between cattle with low and high RFI in both trials. These data suggest that ADP has greater control of oxidative phosphorylation in liver mitochondrial of cattle with low RFI compared to their high RFI counterparts.

Effect of rate of weight gain of steers during the stocker phase. III. Gene expression of adipose tissues and skeletal muscle in growing-finishing beef cattle.

The objective of this study was to determine the impact of stocker production systems differing in growth rate on differential adipogenic and lipogenic gene expression of intramuscular (IM), subcutaneous (SC), and perirenal (PR) adipose tissues. Angus steers were assigned to 4 stocker cattle production systems in 2 consecutive years: 1) cottonseed meal-based supplement while grazing dormant native range (CON), 2) ground corn/soybean meal-based supplement while grazing dormant native range (CORN), 3) grazing wheat pasture at a high stocking rate for a low rate of BW gain (LGWP), and 4) grazing wheat pasture at a low stocking rate for a high rate of BW gain (HGWP). Steers were harvested during the stocker phase at similar age (different carcass weight) in Exp. 1 (3 steers/treatment) or at similar carcass weight in Exp. 2 (4 steers/treatment). Adipose tissues were analyzed for mRNA expression of adipogenic (peroxisome proliferator activated receptor γ [PPARγ], sterol regulatory element binding factor 1 [SREBF1], CAATT/enhancer binding protein ß, and delta-like homolog 1) and lipogenic (glycerol-3-phosphate dehydrogenase [GPDH], fatty acid synthase [FASN], and diacylglycerol acyltransferase 2 [DGAT2]) genes. Multivariate analysis was used to evaluate the expression of adipogenic or lipogenic genes collectively. There was not a treatment × adipose tissue interaction (F-test, P > 0.15) when steers were harvested at similar age, but a treatment × adipose tissue interaction (F-test, P < 0.05) was evident when steers were harvested at similar carcass weight. At similar carcass weight, treatment had no effect (P > 0.10) on the canonical variate of adipogenic or lipogenic mRNA expression in IM adipose tissue, but faster rates of gain of LGWP and HGWP steers increased (P < 0.10) the canonical variate of adipogenic and lipogenic mRNA expression in SC and PR adipose tissue compared with CON and CORN steers. Strong positive correlations (P < 0.05) of PPARγ, SREBF1, GPDH, FASN, and DGAT2 mRNA expression with the canonical variate indicate that these genes strongly influenced differences between treatments and adipose tissues. These results suggest that contrary to our hypothesis rate of gain has little influence on differentiation and lipid synthesis of IM adipose tissue at similar carcass weight but faster rates of gain increase differentiation and lipid synthesis of SC and PR adipose tissue even at similar carcass weight.

Effect of rate of body weight gain in steers during the stocker phase. I. Growth, partitioning of fat among depots, and carcass characteristics of growing-finishing beef cattle.

Two experiments were conducted to examine the effect of growth rate to similar age or BW on fat deposition in stocker cattle grazing dormant native range (DNR) or winter wheat pasture (WP). In each experiment, fall-weaned Angus steers were randomly allotted to 1 of 4 stocker production programs: 1) control, 1.02 kg/d of a 40% CP cottonseed meal-based supplement during grazing of DNR (CON); 2) corn/soybean meal-based supplement fed at 1% of BW during grazing of DNR (CORN); 3) grazing WP at a high stocking rate to achieve a low rate of BW gain (LGWP); and 4) grazing WP at a low stocking rate to achieve a high rate of BW gain (HGWP). In Exp. 1, a subset of steers (3 steers per treatment) was harvested after winter grazing (138 d) at similar age. The remaining WP steers were transitioned into the finishing phase, whereas DNR steers were allowed to graze the same native range pastures for another 115 d without supplementation before entering the feedyard. In Exp. 2, steers grazed their respective pastures until each treatment reached an estimated HCW of 200 kg (262, 180, 142, and 74 d, respectively, for the CON, CORN, LGWP, and HGWP treatments), at which time a subset of steers (4 steers per treatment) were selected for intermediate harvest before finishing. In both experiments, the remaining steers were fed a finishing diet to a common 12th-rib fat thickness of 1.27 cm. In Exp. 1, winter grazing ADG was 0.19, 0.52, 0.68, and 1.37 ± 0.03 kg/d; and in Exp. 2, winter/summer grazing ADG was 0.46, 0.61, 0.83, and 1.29 ± 0.02 kg/d, respectively for CON, CORN, LGWP, and HGWP treatments. At intermediate harvest in Exp. 1, HGWP steers had greater (P < 0.01) 12th-rib fat thickness and marbling scores, compared with the other treatments. However, in Exp. 2, LGWP steers had greater (P < 0.01) marbling scores compared with HGWP steers, which were greater than DNR steers. At final harvest in Exp. 1, LGWP steers had greater (P < 0.01) 12th-rib fat thickness and smaller LM area, compared with the other treatments; however, there were no differences (P = 0.99) in final marbling scores. In Exp. 2, CON steers had lower (P < 0.05) 12th-rib fat thickness and tended (P = 0.10) to have greater marbling scores, compared with the other treatments. These data suggest that changes in the partitioning of fat among depots during the stocker phase may not be reflected after finishing when steers are fed to a common 12th-rib fat thickness.

Effect of rate of body weight gain of steers during the stocker phase. II. Visceral organ mass and body composition of growing-finishing beef cattle.

Two experiments were conducted to examine the effect of rate of BW gain during the stocker phase on visceral organ mass and body composition of growing-finishing cattle that had grazed dormant native range (DNR) or winter wheat pasture (WP). In each experiment, fall-weaned steers were allotted randomly to 1 of these stocker production programs: 1) control, 1.02 kg · steer(-1) · d(-1) of a 40% CP cottonseed meal-based supplement during grazing of DNR (CON); 2) corn/soybean meal-based supplement fed at 1% of BW during grazing of DNR (CORN); 3) grazing WP at a high stocking rate to achieve a reduced rate of BW gain (LGWP); and 4) grazing WP at a low stocking rate to achieve an increased rate of BW gain (HGWP). In Exp. 1, 3 steers per treatment were harvested after winter grazing (138 d). The remaining WP steers were transitioned into a finishing phase and DNR steers were allowed to graze the same pastures for another 115 d before entering a feedyard. In Exp. 2, steers grazed respective pastures until each treatment reached an estimated HCW of 200 kg (262, 180, 142, and 74 d, respectively, for CON, CORN, LGWP, and HGWP treatments), at which time 4 steers per treatment were randomly selected for intermediate harvest before finishing. At the end of the finishing period, 4 additional steers from each treatment were randomly selected for final carcass measurements. All steers were fed to a common 12th rib fat thickness of 1.27 cm. After winter grazing in Exp. 1, HGWP steers had the greatest (P < 0.01) mesenteric/omental fat, total viscera, total splanchnic tissue mass, and carcass and empty body fat, compared with the other treatments. In Exp. 2 at intermediate harvest, WP steers had greater (P < 0.03) mesenteric/omental fat, total viscera, and total splanchnic tissue mass, compared with CORN steers, with CON steers being intermediate. Also, the WP steers had greater (P < 0.02) carcass and empty body fat, compared with CORN steers, with CON steers being intermediate. At final harvest in Exp. 2, LGWP steers had the least total viscera and total splanchnic tissue mass, compared with the other treatments. However, there were no differences (P > 0.53) among treatments for carcass or empty body fat. Stocker systems using WP or DNR result in cattle with differences in body fat and visceral organ mass before finishing; this may influence feedlot efficiency, even though there were no differences in body fat and visceral organ mass at the end of the finishing period.

Effects of starch- vs. fiber-based energy supplements during winter grazing on partitioning of fat among depots and adipose tissue gene expression in growing cattle and final carcass characteristics.

Fifty-five normal-weaned Angus steers (268 ± 22 kg; 265 ± 16 d of age) were used to evaluate the effects of starch- vs. fiber-based energy supplements for stocker cattle grazing low-quality dormant native range on growth performance, body composition, and adipose tissue development of different fat depots. Steers were randomly allotted to 4 treatments: 1.02 kg·steer(-1)·d(-1) of a 40% CP cottonseed meal-based supplement (CON), corn/soybean meal-based supplement fed at 1% of BW (CORN), soybean hull/soybean meal-based supplement fed at 1% of BW (SBH), or dried distillers grains with solubles fed at 1% of BW (DDGS). All supplements were individually fed 5 d/wk during the 121-d winter grazing phase. After winter grazing, 3 steers per treatment were harvested to determine body composition and carcass characteristics, and collect subcutaneous (SC) and perirenal (PR) adipose tissue samples. The remaining steers grazed cool-season grass pastures for 74 d without supplementation before finishing. Steers were fed a common finishing diet for 113 d before harvest, at which time carcass characteristics were collected at a commercial abattoir. Energy supplementation increased (P < 0.01) winter grazing ADG compared with CON steers, and CORN steers had greater (P < 0.01) ADG than SBH and DDGS steers. Energy supplementation increased (P < 0.04) mesenteric/omental fat mass but did not influence (P > 0.13) 12th rib fat thickness or marbling score at intermediate harvest compared with CON steers. The mRNA expression of genes involved in lipogenesis and markers of adipogenesis were greater (P < 0.05) in PR adipose tissue of energy-supplemented steers compared with CON steers but not in SC adipose tissue. Fiber-supplemented steers had greater (P < 0.01) mRNA expression of fatty acid synthase and fatty acid binding protein 4 compared with CORN steers in PR adipose tissue but not SC adipose tissue. At final harvest, energy-supplemented steers had greater (P < 0.05) KPH and yield grade than CON steers, but no differences (P = 0.75) in marbling score were observed. Neither energy supplementation nor type of energy supplement influenced intramuscular fat deposition in stocker cattle grazing dormant native range. These data suggest that the total energy intake and stage of animal maturity during grazing supplementation were not great enough to influence marbling deposition.

Quality evaluation of beef carcasses produced under tropical conditions of México.

Twenty-three thousand four hundred eighty-four beef carcasses were classified according to the Mexican norm NMX-FF-078-SCFI-2002 at the No. 51 Federal Inspected Type abattoir located in the State of Tabasco, Mexico, owned by the Beef Cattle Union of Tabasco State. Tabasco State has a Tropical humid (Am) and subhumid (Aw) climate with rains in summer. The study took place between November 2009 and February 2010. The objective of this study was to evaluate independently the influence of each of the grading criteria used for classification on the final quality grade and determine areas for improvement to enhance the quality of Mexican beef carcasses. The beef carcass norm implementation followed a mechanistic approach of the 5 basic evaluation criteria applied in the sequential order: 1) maturity (age), 2) conformation (muscularity), 3) color of the meat, 4) fat color, and 5) distribution of the subcutaneous fat. The quality grades possible were Supreme, Select, Standard, Commercial, Out of Grade, and Veal. The proportion of carcasses classified as Select, Standard, Commercial, Out of Grade, and Veal were 13.4, 45.8, 27.4, 10.6, and 2.7%, respectively. No carcasses had a final quality grade of Supreme. Based on maturity, 79.2% of the carcasses met the specifications for Supreme; however, when the next criterion, conformation, was evaluated only 0.5% of the carcasses met the specifications for Supreme. When carcasses with a criterion grade of Supreme are not included in the analysis, the γ and κ statistics indicated that maturity and conformation have the greatest association and agreement, respectively, with final quality grade. When carcasses with a criterion grade of Supreme are included in the analysis, the κ statistic for the assessment of agreement between final quality grade and criterion indicated a descending order of conformation, subcutaneous fat distribution, maturity, meat color, and fat color. Thus, based on the degree of association and agreement, conformation was identified as the criterion with the greatest influence on final quality grade and the primary reason for the absence of Supreme grading among the carcasses studied. It is concluded that the application of the Mexican beef carcass classification norm NMX-FF-078-SCFI-2002 into a sample population of beef cattle coming out of a tropical beef production environment highlights a system capable of sending animals to slaughter at an early age with adequate meat and fat color and subcutaneous fat distribution although requiring improvement in conformation.

Relationships between feed efficiency, scrotal circumference, and semen quality traits in yearling bulls.

A meta-analysis was conducted to examine phenotypic relationships between feed efficiency, scrotal circumference, and semen quality traits in yearling bulls. Data evaluated were obtained from 5 postweaning trials involving Angus (n = 92), Bonsmara (n = 62), and Santa Gertrudis (n = 50) bulls fed diets that ranged from 1.70 to 2.85 Mcal ME/kg DM. After an adaptation period of 24 to 28 d, feed intake was measured daily, and BW was measured at 7- or 14-d intervals during the 70- to 77-d trials. Ultrasound carcass traits (12th-rib back fat thickness, BF; LM area, LMA) and scrotal circumference (SC) were measured at the start and end of each trial. Semen samples were collected by electroejaculation within 51 d of the end of the trials when the age of bulls averaged from 365 to 444 d and were evaluated for progressive sperm motility and morphology. Residual feed intake (RFI) was calculated as the difference between actual DMI and expected DMI from linear regression of DMI on ADG and midtest BW(0.75), with trial, trial by ADG, and trial by midtest BW(0.75) as random effects. Across all studies, bulls with low RFI phenotypes (<0.5 SD below the mean RFI of 0) consumed 20% less DM and had 10% less BF but had similar ADG, SC, and semen quality traits compared with high-RFI bulls (>0.5 SD above the mean RFI of 0). Gain to feed ratio was strongly correlated with ADG (0.60) and weakly correlated with initial BW (-0.17) and DMI (-0.26). Residual feed intake was not correlated with ADG, initial age, or BW but was correlated with DMI (0.71), G:F (-0.70), and BF (0.20). Initial SC (-0.20), gain in SC (-0.28), and percent normal sperm (-0.17) were correlated with G:F, but only sperm morphology was found to be weakly associated with RFI (0.13). These data suggest that RFI is not phenotypically associated with SC or sperm motility but is weakly associated with sperm morphology.

Effects of winter growing program on visceral organ mass, composition, and oxygen consumption of beef steers during growing and finishing.

The purpose of this experiment was to investigate the effects of winter growing program on organ mass, composition, and oxygen consumption in beef steers. A total of 46 steers were used for the experiment. Four steers were randomly selected as an initial slaughter group. Remaining steers were randomly allotted to 1 of 4 treatment groups: 1) fed a high-concentrate diet for ad libitum intake (CF); 2) grazed on wheat pasture (WP); 3) fed a sorghum silage-based growing diet (SF); or 4) program fed a high-concentrate diet (PF). Steers in the WP, SF, and PF groups were managed to achieve approximately equal rates of BW gain during the growing phase. After the growing phase (112 d), steers in the WP, SF, and PF treatments were adapted to a high-concentrate diet for finishing. Steers from all treatments were slaughtered at a fat thickness of 1.27 cm as estimated by ultrasound. In addition, 6 steers from each treatment were randomly selected for slaughter at the end of the growing phase. Weights of all individual organs were measured and tissue samples of duodenum and liver collected. At the end of the growing phase, WP steers had greater (P < 0.05) small intestine, liver, and kidney mass than SF and PF steers. In contrast, mesenteric fat mass and total visceral fat content were greatest (P < 0.01) for PF, intermediate for SF, and least for WP steers. Mass of total viscera and total splanchnic tissues (TST) did not differ (P > 0.10) among treatments. At final slaughter, mass of mesenteric fat, total viscera, and TST were similar among treatments, but liver weights remained greatest (g/kg of empty BW; P < 0.01) for WP steers. There were no differences in oxygen consumption of duodenum or liver tissue on an equal weight basis (microL.min(-1.)g(-1)) at the end of either period. Growing program affected mass of components of the TST at the end of the growing phase, which contributed to differences in rate of splanchnic organ growth during finishing. We conclude that program feeding a high-concentrate diet during the growing phase may result in greater ADG and G:F during the subsequent finishing period compared with forage-based diets due to less accretion of visceral organ mass resulting in reduced maintenance energy requirements during finishing.

Effects of winter growing programs on subsequent feedlot performance, carcass characteristics, body composition, and energy requirements of beef steers.

The purpose of this study was to investigate the effects of winter growing program on subsequent finishing performance, carcass merit, and body composition of beef steers. Four steers were slaughtered to determine initial body composition. Remaining steers (n = 256) were blocked by BW and randomly allotted to 1 of 4 treatment groups: 1) ad libitum fed a high-concentrate diet (CF), 2) grazed on wheat pasture (WP), 3) fed a sorghum silage-based diet (SF), or 4) program fed a high-concentrate diet (PF). Steers in the WP, SF, and PF groups were managed to achieve approximately equal rates of BW gain. After the growing phase (112 d), 6 steers were randomly selected from the WP, SF, and PF treatments for determination of body composition. Remaining steers were adapted to a high-concentrate diet for finishing and slaughtered at 1.27 cm of 12th-rib fat. Six steers from each treatment were used to determine carcass, offal, and empty body composition. During the growing phase, WP, SF, and PF steers gained 1.15, 1.10, and 1.18 kg/d, respectively, and ME intake did not differ (P = 0.50) among treatments. Program-fed and SF steers had greater (P < 0.05) offal and empty body fat content than WP steers. Gain in offal and empty body fat was greatest (P < 0.05) for PF steers, intermediate for SF steers, and least for WP steers. During the finishing phase (123, 104, 104, 196 d for WP, SF, PF, and CF, respectively) DMI was greater (P < 0.01) for SF steers (10.9 kg/d) than for PF steers (10.1 kg/d); WP steers were intermediate (10.4 kg/d). Daily BW gain was greatest (P < 0.05) for SF steers (2.02 kg/d), intermediate for PF steers (1.85 kg/d), and least for WP and CF steers (1.64 and 1.63 kg/d, respectively). Accretion (kg/d) of carcass and empty body mass was less (P < 0.05) for WP and CF steers compared with PF and SF steers. Calf-fed steers had greater (P < 0.05) fat content of offal than SF and PF steers; WP steers were intermediate. Gain in empty body and carcass energy (Mcal/d) was greater (P < 0.05) for PF steers than CF steers with SF and WP steers being intermediate. At slaughter, SF steers had reduced (P < 0.01) yield grades and greater marbling scores compared with CF and WP steers; PF steers were intermediate. In conclusion, growing programs that increase fat composition of feeder calves did not negatively affect subsequent finishing performance. Finishing steers as calves may reduce retained energy of carcass tissues and increase internal fat during high-grain feeding compared with steers that previously underwent a growing program.

Phenotypic and genetic relationships of residual feed intake with performance and ultrasound carcass traits in Brangus heifers.

The objective of this study was to characterize residual feed intake (RFI) and to estimate phenotypic and genetic correlations with performance and ultrasound carcass traits in growing heifers. Four postweaning feed efficiency trials were conducted using 468 Brangus heifers. The complete Brangus pedigree file from Camp Cooley Ranch (Franklin, TX), which included 31,215 animals, was used to generate genetic parameter estimates. The heifer progeny from 223 dams were sired by 36 bulls, whereas the complete pedigree file contained 1,710 sires and 8,191 dams. Heifers were individually fed a roughage-based diet (ME = 1.98 Mcal/kg of DM) using Calan gate feeders for 70 d. Heifer BW was recorded weekly and ultrasound measures of 12th- to 13th-rib fat thickness (BF) and LM area (LMA) obtained at d 0 and 70. Residual feed intake (RFIp) was computed as actual minus predicted DMI, with predicted DMI determined by linear regression of DMI on mid-test BW(0.75) (MBW) and ADG with trial, trial x MBW, and trial x ADG as random effects. Overall means for ADG, DMI, and RFI were 1.01 (SD = 0.15), 9.51 (SD = 1.02), and 0.00 (SD = 0.71) kg/d, respectively. Stepwise regression analysis revealed that inclusion of gain in BF and final LMA into the base model increased the R(2) (0.578 vs. 0.534) and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted RFI (RFIc) were strongly correlated phenotypically and genetically with DMI and FCR, but not with ADG or MBW. Gain in BF was phenotypically correlated (P < 0.05) with RFIp (0.22), but not with FCR or RFIc; however, final BF was genetically correlated (P < 0.05) with RFIp (0.36) and RFIc (0.39). Gain in LMA was weakly phenotypically correlated with FCR, but not with RFIp or RFIc; however, gain in LMA was strongly genetically correlated with RFIp (0.55) and RFIc (0.77). The Spearman rank correlation between RFIp and RFIc was high (0.96). These results suggest that adjusting RFI for ultrasound carcass composition traits will facilitate selection phenotypically independent of growth, body size, and carcass composition; however, genetic relationships may still exist between RFI and carcass composition.

Relationship between feeding behavior and residual feed intake in growing Brangus heifers.

Residual feed intake (RFI) is a measure of feed efficiency defined as the difference between actual feed intake and expected feed intake required for maintenance and production. The objective of this study was to determine the relationship between RFI, feeding behavior, and other performance traits in growing heifers. Individual DMI was measured in Brangus heifers (n = 115) fed a roughage-based diet (ME = 2.0 Mcal/kg) for 70 d using Calan-gate feeders. Residual feed intake was computed as the residuals from linear regression of DMI on mid-test BW(0.75) and ADG. Heifers with the greatest (least efficient, n = 18) and least (most efficient, n = 18) RFI were identified for quantification of feeding behavior traits. Continuous video recordings were obtained for all heifers during d 28 through d 56 of the 70-d feeding trial. Video data of 2 replications of four 24-h periods, 2 wk apart, were analyzed for the focal heifers. A head-down feeding event was defined as a heifer positioned in the feeder with her head lowered. A meal included all head-down feeding events that were separated by less than 300 s. The mean RFI for the high- and low-RFI heifers were 1.00 and -1.03 +/- 0.03 kg/d, respectively. High-RFI heifers consumed 21.9% more (P < 0.0001) DM but had similar BW and ADG compared with low-RFI heifers. The high-RFI heifers spent less time in head-down feeding events per day (P < 0.0001; 124 vs. 152 +/- 4.3 min/d), consumed DM at a faster rate (99.6 vs. 62.8 +/- 3.3 g/min), and ate more often per day (119.1 vs. 90.5 +/- 3.9 head-down feeding events/d) compared with the low-RFI heifers; however, meal duration and frequency were not related to RFI. We conclude that feeding behavior related to head-down feeding events may be more useful as an indicator of RFI than the number of meal events.