Prediction of slaughter cow composition using live animal and carcass traits

Changes in ultrasound measures of muscle and its genetic variation during lactation in dairy cows

Changes in ultrasound measures of muscle area (UtM) during lactation in different breeds and parities and with different feeding levels were examined. Random regressions were fitted to repeated measures of UtM in order to study changes in variance components of UtM during lactation. Correlations between measures taken in different stages of lactation and in different parities were also calculated. The shape of UtM curves during lactation appeared to be fairly consistent for all breeds and parities. The lowest point of all curves coincided with the expected nadir of body reserves during lactation. With lower-than-normal feeding level, the drop of UtM after calving was deeper and the overall level was lower. A major proportion of the variance in UtM was found to be determined by additive genetic variation. In all three breeds studied, repeatability and heritability estimates were high and fairly consistent during lactation and between parities. The very high genetic correlations between measures taken in different periods of lactation suggested that muscle growth and recovery are controlled by the same gene complex throughout lactation.

Our results suggest that UtM, if used jointly with other body measures such as body condition score, could be a useful indicator of tissue mobilization and deposition in the lactating cow, especially during the early stage of lactation.

The chemical composition of carcasses can be predicted from proxy traits in finishing male beef cattle: A meta-analysis

Management practices can contribute to improving carcass quality if carcass quality could be simply evaluated under a wide range of conditions. The objective of this study was to derive quantitative relationships between the most accurate (but laborious) measurements of carcass chemical composition and proxy traits easily obtainable at slaughter (yield grade, subcutaneous fat thickness, marbling, ribeye area and hot carcass weight) by meta-analysis. Data from 34 publications using male beef cattle were used to develop and validate the models. The breeds were characterized according to origin, rate of maturity, production purpose and frame size. The results indicated that the changes in carcass fat and protein can be predicted from the yield grade or subcutaneous fat thickness, and hot carcass weight, with prediction errors ranging between 9 and 12%. Including the breed characteristics in the models did not improve the fit. The relationships are applicable to group values of male beef cattle having light and fatty carcasses from early-maturing British breeds.

Characterization of Canadian grade standards and lean yield prediction for cows

Rodas-González, A., Juárez, M., Robertson, W. M., Larsen, I. L. and Aalhus, J. L. 2013. Characterization of Canadian grade standards and lean yield prediction for cows. Can. J. Anim. Sci. 93: 99–107. Commercial carcasses (n=120) were selected to benchmark the current Canadian grading system for cows (D1, D2, D3, D4;>50% ossification) in comparison to A/AA grades youthful carcasses [over (OTM) and under (UTM) 30 mo of age based on dentition but <50% ossification]. With the exception of the D3 and D4 grades, D1 and D2 carcass grades had similar carcass yield attributes compared with OTM and UTM carcasses; however, rib-eye area from UTM carcasses was the largest (P<0.05), followed by D1, D2 and OTM. As expected, both OTM and UTM grades had lower ossification scores (P<0.05); however, D4 grade showed the highest marbling score (P<0.05). For carcass composition, compared with all other grades, the D3 grade had the highest proportion of lean (P<0.05) due to a lower proportion of dissectible fat (P<0.05); however, it had the lightest carcass weight (P<0.05). Using simple measures of carcass characteristics (grade fat, rib-eye area, marbling and ossification) a prediction equation to estimate lean yield (R 2=0.825; Cp=4.31) could be used to more accurately assess carcass value in cows; however, validation of the equation on a separate population would be required before its application.

Correlations Among Body Condition Scores from Various Sources, Dairy Form, and Cow Health from the United States and Denmark

The objectives of this study were to estimate genetic correlations among body condition scores (BCS) from various sources, dairy form, and measures of cow health. Body condition score and dairy form evaluated during routine type appraisal was obtained from the Holstein Association USA, Inc. A second set of BCS was obtained from Dairy Records Managements Systems (DRMS) and was recorded by producers that use PCDART dairy management software. Disease observations were obtained from recorded veterinarian treatments in several dairy herds in the United States. Estimated breeding values for diseases in Denmark were also obtained. Genetic correlations among BCS, dairy form, and cow health traits in the United States were generated with sire models. Models included fixed effects for age, DIM, and contemporary group. Random effects included sire, permanent environment, herd-year season for health traits, and error. Predicted transmitting abilities (PTA) for BCS and dairy form were correlated with estimated breeding values for disease in Denmark. The genetic correlation estimate between BCS from DRMS and BCS from the Holstein Association USA, Inc., was 0.85. The genetic correlation estimate between BCS and a composite of all diseases in the United States was -0.79, and PTA for BCS was favorably correlated with an index of resistance to disease other than mastitis in Denmark (0.27). Dairy form was positively correlated with a composite of all diseases in the United States (0.85) and was unfavorably correlated with an index for resistance to disease other than mastitis in Denmark (-0.29). Adjustment for protein yield PTA had a minimal affect on correlations between PTA for BCS or dairy form and disease in Denmark. Selection for higher body condition or lower dairy form with continued selection for yield may slow deterioration in cow health as a correlated response to selection for increased yield.