Genotype by Country Interaction for Birth and Weaning Weights for Shorthorn Cattle in Australia and the United States

Birth (BW) and weaning weights (WW) of Shorthorn beef cattle used to study the genotype by country (G´C) interactions between Australia (AU) and the United States (US). Data were collected depending on the connectedness on genetic links of common sires. The edited data consisted of numbers of sire, dam and calf of 2,013, 19,784 and 42,963 in AU and 4,797, 38,648 and 95,849 in the US, respectively. After that, sets of data were combined together and corresponding traits from different countries were treated as different traits. Therefore, a bivariate animal model including maternal genetic and permanent environment effects was used to study the interactions. No covariance due to maternal permanent environmental and environmental effects {cov(pe1,pe2) and cov(e1,e2) = 0} was assumed. Estimates of (co)variance components have been done by restricted maximum likelihood. Variance component estimates of the same trait across countries were slightly different. Direct and maternal genetic correlations (in parentheses) between corresponding traits were 0.93 (0.93) and 0.78 (0.86) for BW and WW, respectively. This implied that a joint BW genetic evaluation could be conducted using a model that treated the information as a single population. For WW, sires across AU and the US needed evaluation to consider carefully the G´C interactions.