ALBERT

Description: SUMMARYHereford (H × H), Brahman × Hereford (B × H), Simmental × Hereford (S × H) and Friesian × Hereford (F × H) females born over a 5-year period (1973–77) were placed on pastures of high, medium or low nutritive value at Grafton, New South Wales, Australia, at weaning (7–8 months of age). The first mating of heifers on high pasture was at 15 months (1974) while that on medium and low pastures was delayed until 27 months of age (1975). This paper reports the reproductive performance of these cows up to 5 years of age and the preweaning growth of their calves which were sired by Hereford bulls at Grafton, Australia. In total, 1222 calving records were analysed.Most traits were subject to interaction between genotype and other main effects (pasture, year of birth of cow, cow age and sex of calf). Eyelid pigmentation was an exception, with calves from B × H cows having more than calves of other genotypes (73 v. 43%). There were significant genotype differences in calving difficulty among 2-year-old heifers only, with H × H (33%) requiring more assistance than F × H (15%) and SxH (10%) heifers, while B × H heifers did not require any assistance. Genotype differences in percentage of calves born and weaned were observed on low pastures only, where B × H (66% born, 65% weaned) exceeded H × H (48%, 39%) and S × H (39%, 38%) cows, with F × H (58%, 50%) cows being intermediate. Calves by H × H cows were the slowest-growing and were the lightest at weaning on all pastures, with mean gains of 759, 604 and 340 g/day, and mean weaning weights of 212, 188 and 110 kg, on high, medium and low quality pastures, respectively. F × H and S × H cows produced the fastest-growing calves on high quality pasture (966 and 936 g/day, respectively) while B × H cows produced the fastest-growing calves on medium (823 g/day) and low (679 g/day) quality pastures. F × H cows weaned the heaviest calves on high quality pasture (274 kg) while F × H and B × H weaned the heaviest calves on medium (230 and 229 kg, respectively) and low (162 and 169 kg, respectively) quality pastures. Differences in body measurements followed a pattern similar to weaning weight.

Description: SUMMARYThe 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 FxH (Brahman, 238kg; Hereford, 238kg) dams. For HxH 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 FxH, 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 HxH dams. On medium quality pasture, weaning weight of calves of crossbred dams (B x H, S x H and FxH) 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.

Description: Milk yield was determined by the weigh-suckle-weigh method over 2 years (1983 and 1984 calvings), for a total of 305 purebred Hereford (H×H) and first-cross Brahman×Hereford (B×H), Simmental×Hereford (S×H) and Friesian×Hereford (F×H) cows grazing three pasture systems at Grafton, New South Wales, Australia. The age of the cows ranged from 6 to 11 years. The data were used to evaluate different estimates of milk yield and to examine the effects of milk yield on growth of calves up to weaning.Of all the cow traits studied, average lactation milk yield (average of early, mid and late-lactation milk yields) had the highest correlation coefficient with calf 210-day weight (r=0·73) and pre-weaning average daily gain (ADGtotal, r=0·73), and explained 〉50% of the variation in the calf traits. However, milk yield was also moderately correlated with other cow traits (liveweight and body condition score). Thus, to predict calf performance, milk yield data may not be required if detailed data on other cow traits are available. This is supported by the finding that differences in the coefficients of determination (R2) between models for calf 210-day weight and ADGtotal which included average lactation milk yield and other cow traits (highest R2=69%) and models which included other cow traits but no milk yield estimate (highest R2=57%) were