Growth of Mashona cattle on range in Zimbabwe. II. Estimates of genetic parameters and predicted response to selection.

For 1,456 Mashona calves sired by 88 bulls heritability estimates from paternal half-sibs were 0.44 +/- 0.11 for birth weight, 0.38 +/- 0.10 for 205-day weaning weight, 0.39 +/- 0.10 for 18-month weight, 0.37 +/- 0.10 for pre-weaning daily liveweight gain and 0.41 +/- 0.11 for daily gain from weaning to 18 months of age. Genetic correlations were relatively low for birth weight with weaning weight (0.42 +/- 0.18), 18-month weight (0.56 +/- 0.16), pre-weaning gain (0.33 +/- 0.19) and post-weaning gain (0.36 +/- 0.19). Higher genetic correlations were observed for pre-weaning gain with weaning weight (0.98 +/- 0.01) and 18-month weight (0.59 +/- 0.14) and for 18-month weight with weaning weight (0.67 +/- 0.12) and post-weaning gain (0.73 +/- 0.10). Post-weaning daily gain was not significantly correlated genetically with both pre-weaning gain (-0.11 +/- 0.22) and weaning weight (-0.03 +/- 0.22). With 10% retention of males and 60% of females expected genetic improvements per generation from direct selection for weaning weight or 18-month weight were 8.11 kg and 12.12 kg respectively. These improvements would be reduced by 18% and 35% if selection indices were used to produce no correlated change in birth weight.