EVALUATION OF BOS-INDICUS AND BOS-TAURUS STRAIGHTBREDS AND CROSSES .3. DIRECT AND MATERNAL GENETIC-EFFECTS ON GROWTH TRAITS

Data on Brahman and Hereford cattle and their crosses were used to est imate direct additive, direct heterosis, maternal additive and materna l heterosis effects for pre-weaning and post-weaning liveweights, aver age daily gain (ADG) and height at various ages. The cattle were born at Grafton, N.S.W., and raised on high, medium and low quality pasture s until weaning. During the post-weaning period, the steers were grown in three environments in New South Wales, while the heifers remained at Grafton. Genetic effects were estimated by regression and the addit ive components expressed as deviations from Hereford effect. Weaning w eight and pre-weaning ADG of Hereford calves (both sexes) were 237.8 k g and 827 g/day on high, 210.5 kg and 704 g/day on medium, and 128.3 k g and 425 g/day on low quality pastures respectively. Post-weaning ADG of Hereford steers (weaning to 36 months) and heifers (weaning to 30 months) was 296 and 240 g/day respectively. Direct heterosis was signi ficant (P<0.05) for most traits. Estimates of direct heterosis for wea ning weight were 24.9 and 20.2 kg, and for pre-weaning ADG were 79 and 68 g/day, on high and medium quality pastures respectively. Direct he terosis for ADG of steers (weaning to 36 months) and heifers (weaning to 30 months) was 91 and 76 g/day respectively. Estimates of maternal heterosis for weaning weights were 14.9, 30.9 and 37.8 kg and for pre- weaning ADC were 31 (not significant), 105 arid 153 g/day, for high, m edium and low quality pastures respectively. Maternal heterosis for AD G of steers (weaning to 36 months) was -47 g/day. There was a negative direct additive effect on post-weaning ADG in environments where past ure quality was good, but the effect was not significant on poor quali ty pasture. Maternal additive effect was negative for birth weight for high and medium quality pastures and positive for weaning weight and pre-weaning ADG on low quality pasture. The performance of untested cr osses can be predicted from the estimates and models provided.