MULTIPLE-BREED GENETIC EVALUATION OF GROWTH TRAITS IN SIMMENTAL AND SIMBRAH CATTLE

Abstract

Covariance components and genetic parameters were estimated in Simmental, Simbrah and Simmental x Zebu calves fitting six alternative models to birth weight (BW; n=105,297), 205-day weight (WW; n=82,752) and 365-day weight data (YW; n=49,450) provided by Asociación Mexicana de Criadores de Ganado Simmental Simbrah, A.C. Models ranged from a model which included direct additive genetic effects (Model 1) to a model which included direct and maternal additive genetic effects, their covariance and maternal permanent environmental effects (Model 6). Fixed effects were: contemporary group, age of dam, proportion of Simmental genes, heterozygosity and recombination losses. Estimates of direct and maternal heritability varied between alternative models. Due to the problems associated with the estimation of the direct-maternal correlation, which was extremely high (absolute value), Model 4, which included both dams’ genetic and permanent environmental effects in addition to direct additive genetic effects, was considered to be the most appropriate for all traits. Application of any of the other models would result in inaccurate expected progeny differences, affecting selection efficiency. Model-4 estimates of direct heritability, maternal heritability and of the ratio of maternal permanent environmental variance to the total phenotypic variance were: 0.17, 0.01 and 0.03; 0.14, 0.02 and 0.04; and 0.15, 0.01 and 0.01 for BW, WW and YW, respectively.