Abstract

Best linear unbiased predictors (BLUP) of breeding values for additive direct and additive maternal genetic effects were estimated from pedigree birth weight (BWT) records 4272 in indigenous Nguni cattle born between 1988 and 1997. Data was partitioned according to sex and breeding values for direct additive and maternal additive were estimated using a univariate animal model. Estimates of sex specific genetic trends for direct and maternal effects were obtained by averaging corresponding breeding values for partitioned data for animals born in a given year, and regressing these averages on their year of birth. The regression of average direct breeding values on year for males and females was –0.0236 kg/yr and –0.1263 kg/yr, respectively, and the regression of average maternal breeding values on year of birth were -0.0355 kg/yr and –0.0173 kg/yr for males and females, respectively. Environmental trends observed a positive trend for both sexes but was non significant. Estimation of sex specific variance components had no significant influence on the direction and magnitude of genetic trends and indication of homogeneity of variance by sex for birth weight in this population.

Key words: Variance components, sex, trends, birth, Nguni.