Abstract:

Data on live weights collected over a 25-year period (1950-1974) at Serere Agricultural and Animal Production Research Institute. Uganda were used to estimate phenotypic, genetic and environmental trends, and genetic progress in growth traits of the Small East African Zebu (SEAZ). Data were for 1421 progeny. The traits studied were birth weight and live weights at 3 months interval up to 30 months of age. Fixed effects fitted in the statistical models were sex, year of birth, month within year and parity. Least squares mean estimates were obtained by the GLM procedure of SAS. Variance and covariance components were estimated using AIREML procedure, fitting a sire model and individual animal models allowing for both additive and maternal effects and their covariance. The breeding values for all animals were obtained using the later package fitting a single trait animal model. Estimates of genetic trends were calculated by regression of the annual averages of breeding values for respective traits on year of birth, while the phenotypic trends were calculated by regression of least squares mean on year of birth. Environmental trends were calculated as the difference between phenotypic and genetic trends. Mean weights were at birth, 19 kg; 122 kg at weaning weight (9 months); 134 kg at one year, 210 kg at 2 years and 246 kg at 2!6 years. Male calves were significantly heavier than females at all ages. Of the environmental effects, sex was by far the most important source of variation in the preweaning phase, followed by year, month within year and parity. In the postweaning phase, year effects were the most important source of variation, followed by month within year, sex and parity. Year and sex were all highly significant for all traits, while month within year was highly significant for all traits except birth weight. Parity was significant for other traits except birth weight and weights at 21 and 30 months of age.