Systematic Environmental Influences and Variances Due to Direct and Maternal Effects and Trends for Yearling Weight in Cattle

Pedigree yearling records from 1021 local Tuli calves born at Matopos Research Station were analyzed for non genetic factors, genetic parame ers and trends on the yearling weight. It was found that s re year of b rth, sex of calf age of dam had s gn f cant effect (p < 0.01) on a growth trait. The nconsistency o literature estimates indicated the importance o est mation o environmental factors that affect yearling weight within specific experimental herds and environment. Model incorporating both direct and maternal additive genetic effect, covariance and correlations of direct-maternal and permanent environmental maternal effects was adopted for the study Direct and maternal heritabi ty est mates of 0.18 ± 0.001 and 0.04 ± 0 001 were observed, respect vely. Direct-maternal genetic correlat on was low and posi ve, 0.07± 0.012. The regression of average direct breeding values on year was almost zero and the regression of average maternal breeding values on year 0.03 kg/yr. Correction of environmental effects was necessary to increase accuracy for selection of yearling weight in local Tuli cattle. Maternal genetic effects should be included in a model of covariance components estimation at 12 months of age. t i , i , i i i ll i f f i f