The performance of Australian Merinos selected for weaning weight after the suspension of selection

Abstract

The present study involved genetic analyses of three lines of Australian Merino sheep previously selected for high and low weaning weights. Direct and correlated responses of lambs and hoggets were evaluated for growth traits and wool weights after selection for high and low weaning weight was suspended following thirty years of selection. The genotypes were also evaluated for their growth and wool performance in two locations, and phenotypic and genetic parameters were determined with emphasis on the importance and influence of maternal effects. Only one model was used in the analyses of the data with six co-variances (residual variance, direct additive variance, maternal additive variance, direct-maternal additive co-variance, permanent environmental variance and temporary environmental variance) fitted. The study revealed that body weight and birth weight have moderate estimates of maternal heritability with the value decreasing with animal age. Maternal effects for wool traits were minimal. Similarly, the permanent maternal environmental effect decreased with age for body weights and had only a small effect on wool traits. Direct additive and maternal correlations between body weights was found to be low and positive and was low and negative for wool traits. These results are in agreement with previously published estimates confirming the importance of maternal effects for body weight parameters.