EVALUATION OF HEREFORD AND 1ST-CROSS COWS ON 3 PASTURE SYSTEMS .2. GROWTH OF HEREFORD AND BRAHMAN SIRED CALVES OUT OF MATURE COWS

The preweaning growth of the progeny of mature cows grazing high, medium or low quality pasture was evaluated. The cows were 5-9 years of age at the beginning of the study and were either purebred Hereford (H x H), first-cross Brahman x Hereford (B x H), Simmental x Hereford (S x H) or Friesian x Hereford (F x H). Hereford and Brahman bulls were mated to these cows for three mating seasons commencing in 1982, at Grafton, New South Wales, Australia. Records on 634 calves born over three consecutive years were used. Most traits were subject to significant sire breed or dam breed effects or their interactions with one or more of the other main effects (pasture, year of birth of calf, cow age and sex of calf). The incidences of calving difficulty and stillbirths were exceptions. Stillbirths (mean of 3.8%) were not affected by any of the effects studied, while calving difficulty was affected only by sex of calf effect (males, 3.9%; females, 0.8%). The mean calving date of Brahman-sired calves was 11.4 days later (P < 0.05) than that of Hereford-sired calves. Differences between Brahman-sired and Hereford-sired calves for weaning weight were not significant for S x H (Brahman, 237 kg; Hereford, 232 kg) and F x H (Brahman, 238 kg; Hereford, 238 kg) dams. For H x H dams however, calves sired by Brahman were heavier at weaning (205 kg) than those sired by Hereford (193 kg) bulls, while for B x H dams the reverse was true (Brahman, 222 kg; Hereford, 231 kg). For calves with B x H dams average daily gain (ADG) was the same (957 g/day) for each sire breed, while for the other dam breeds, Brahman-sired calves had a higher ADG than Hereford-sired calves (862 v. 779, 1014 v. 946 and 1022 v. 950 g/day for H x H, S x H and F x H, respectively). Calves sired by Brahman bulls had > 90% eyelid pigmentation while Hereford-sired calves had 44.74%. On high quality pasture, the weaning weights and ADG of calves of F x H and S x H dams were higher than those of B x H and H x H dams. On medium quality pasture, weaning weight of calves of crossbred dams (B x H, S x H and F x H) were similar but higher than those of H x H dams. On low quality pasture, mean weaning weight of calves of B x H was higher than those of S x H and F x H dams, which in turn, were higher than that of H x H dams.