The performance of Brahman-Shorthorn and Sahiwal-Shorthorn beef cattle in the dry tropics of northern Queensland. 3. Birth weights and growth to weaning

Abstract

The birth weights and weaning weights of Bus indicus cross calves from 4 inter se mated herd groups in a dry tropical environment were studied. The calving season commenced in late October, about 2 weeks before the start of the pasture-growing season. Second and subsequent generations of 112 Brahman and 112 Sahiwal crosses and first backcross, and later generations of 314 Brahman and 314 Sahiwal crosses, were represented. The Bus taurus component of the crosses was primarily Beef Shorthorn. In general, Brahman crosses were heavier at birth and grew faster to weaning than Sahiwal crosses (P<0.05), with consequent advantages in weaning weights of 11 and 6 kg in first backcross and late generation crosses, respectively. There was a birth weight advantage (P<0.05) of 112 crosses over 314 crosses, which was eroded by the time of weaning. Superior growth rates of 314 crosses were primarily expressed in years with greater nutritional stress and appeared to be due to better adaptation to environmental stresses by the calf. The only difference between filial generations was the growth rate advantage (P<0.05) of F2 1/2 crosses over F3 112 crosses, apparently due to suckling of F1 and F2 dams, respectively. Males exhibited an 8% average advantage (P<0.05) over females for all weight and growth traits in late generation calves. Calves with mature dams were 1.8 kg heavier (P<0.05) at birth. This, along with their higher (P<0.05) preweaning growth rate (19-49 g/day), resulted in calves with mature dams being 4-10 kg heavier (P<0.05) at weaning than calves of young cows. Differences between years in birth weights and preweaning growth rates were 125% (P<0.05). Birth weight was affected by nutrition of the dam in late pregnancy (early calves were generally about 1 kg lighter than late calves), and growth of calves was higher in years when the pasture growing season commenced earlier.