Estimation of (Co)variance components and genetic parameters of growth traits in beef cattle

Variance components and genetic parameters of birth weight (BW), weaning weight (WW) and average daily gain (ADG) in a multibreed beef cattle population were estimated by Restricted Maximum Likelihood (REML) procedures. Four different unitrait animal models were fitted ranging from a simple model with the animal direct effects as the only random effect to the model allowing for both genetic and permanent maternal environmental effects. The simple model excluding maternal effects most likely inflated direct heritability estimates. The model that included direct genetic and permanent maternal environmental effects generally best described the data analysed. Estimates of permanent maternal environmental effects were 0.15 (BW), 0.24 (WW) and 0.24 (ADG), the effects were the important factor determining WW and ADG. Direct and maternal genetic correlations were 0.61, -0.53 and -0.79 for BW, WW and ADG, respectively under the model accounted both for maternal genetic and permanent maternal environmental effects.