Genetic relationships between sex-specific traits in beef cattle: Mature weight, weight adjusted for body condition score, height and body condition score of cows, and carcass traits of their steer relatives

Data from the first four cycles of the Germplasm Evaluation Program at the U.S. Meat Animal Research Center (USMARC) were used to investigate genetic relationships between mature weight (MW, n = 37,710), mature weight adjusted for body condition score (AMW, n = 37,676), mature height (HT, n = 37,123), and BCS (n = 37,676) from 4- to 8-yr old cows (n = 1,800) and carcass traits (n = 4,027) measured on their crossbred paternal half-sib steers. Covariance components among traits were estimated using REML. Carcass traits were adjusted for age at slaughter. Estimates of heritability for hot carcass weight (HCWT); percentage of retail product; percentage of fat; percentage of bone; longissimus muscle area; fat thickness adjusted visually; estimated kidney, pelvic, and heart fat percentage; marbling score; Warner-Bratzler shear force; and taste panel tenderness measured on steers were moderate to high (0.26 to 0.65), suggesting that selection for carcass and meat traits could be effective. Estimates of heritability for taste panel flavor and taste panel juiciness were low and negligible (0.05 and 0.01, respectively). Estimates of heritability from cow data over all ages and seasons were high for MW, AMW, and HT (0.52, 0.57, 0.71; respectively) and relatively low for BCS (0.16). Pair-wise analyses for each female mature trait with each carcass trait were done with bivariate animal models. Estimates of genetic correlations between cow mature size and carcass composition or meat quality traits, with the exception of HCWT, were relatively low. Selection for cow mature size (weight and/or height) could be effective and would not be expected to result in much, if any, correlated changes in carcass and meat composition traits. However, genetic correlations of cow traits, with the possible exception of BCS, with HCWT may be too large to ignore. Selection for steers with greater HCWT would lead to larger cows

Current address: Discipline of Genetics

________________________________________________________________________________ Abstract Genetic evaluation of dairy cattle using test-day models is now common internationally. In South Africa a fixed regression test-day model is used to generate breeding values for dairy animals on a routine basis. The model is, however, often criticized for erroneously assuming a standard lactation curve for cows in similar contemporary groups and homogeneity of additive genetic variances across lactation and for its inability to account for persistency of lactation. The random regression test-day model has been suggested as a more appropriate method and is currently implemented by several Interbull member-countries. This review traces the development of random regression methods and their adoption in test-day models. Comparisons are drawn with the fixed regression test-day model. The paper discusses reasons for suggesting the adoption of the random regression approach for dairy cattle evaluation in South Africa and identifies the key areas where research efforts should focus. _______________________________________________________________________________

Random regression test-day model for the analysis of dairy cattle production data in South Africa : Creating the framework

CITATION: Dzomba, E. F., et al. 2010. Random regression test-day model for the analysis of dairy cattle production data in South Africa : creating the framework. South African Journal of Animal Science, 40(4):273-284.The original publication is available at https://journals.co.za/content/sajas/40/4/EJC94760Genetic evaluation of dairy cattle using test-day models is now common internationally. In South Africa a fixed regression test-day model is used to generate breeding values for dairy animals on a routine basis. The model is, however, often criticized for erroneously assuming a standard lactation curve for cows in similar contemporary groups and homogeneity of additive genetic variances across lactation and for its inability to account for persistency of lactation. The random regression test-day model has been suggested as a more appropriate method and is currently implemented by several Interbull member-countries. This review traces the development of random regression methods and their adoption in test-day models. Comparisons are drawn with the fixed regression test-day model. The paper discusses reasons for suggesting the adoption of the random regression approach for dairy cattle evaluation in South Africa and identifies the key areas where research efforts should focus. .Publisher's versio