Sex Specific Genetic and Environmental Trends in Birth Weight of Indigenous Nguni Conservation Cattle Herd of Zimbabwe

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 of 4272 indigenous Nguni cattle of Zimbabwe, born between 1988 and 1997.  Data was partitioned according to sex and breeding values for direct additive and maternal additive and were estimated using an univariate animal models. Estimates of sex specific genetic trends for direct and maternal effects were obtained by averaging corresponding breeding values for partitioned data of animals born in a given year, and regressing these averages on year of birth. The regression of average direct breeding values on year for males and females were –0.0236 and –0.1263 kg/yr, respectively, and the regression of average maternal breeding values on year for birth were -0.0355 and –0.0173 kg/yr for males and females respectively. A positive environmental trend was observed 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 indicating of homogeneity of variance by sex for birth weight in this population.

Keywords: Breeding values, maternal genetic effects, birth weight, Nguni cattle, Zimbabwe