Phenotypic, Genetic and Environmental Trends for Preslaughter Weight and Carcass Traits in Indigenous Matebele Goat

摘要

Mixed model methodology was used to estimate genetic and environmental trends over 21 years for preslaughter weight and carcass traits from 2341 slaughtered indigenous Matebele goats. Maternal breeding values were not considered because they were almost zero. REML estimates of variance components were used to obtain breeding values. The breeding values for direct additive were estimated using an univariate animal model. Estimates of genetic trends for direct effects were obtained by averaging corresponding breeding values for animals born in a given year, and regressing these averages on year of birth (Henderson, 1973), maternal additive genetic effects were not included as a component of genetic trends since its effect was negligible. Environmental trend was directly obtained from the estimates of fixed effects solutions of year of birth. Environmental trends were negative for pre-slaughter weight (-0.25 kg/yr) and hot carcass mass (-0.18 kg/yr), and were positive for cold carcass mass (0.05 cm/yr) and carcass length (0.25 cm/yr) and were all non-significant. Genetic trends were all positive with preslaughter weight having the highest genetic gain of 7 kg/ yr. The environmental trends did not fluctuate much showing the consistence of harsh environmental conditions which characterize the semi-arid tropics.