EVALUATION OF HEREFORD AND 1ST-CROSS COWS ON 3 PASTURE SYSTEMS .1. CALF GROWTH AND REPRODUCTIVE-PERFORMANCE OF YOUNG COWS

Hereford (H x H), Brahman x Hereford (B x H), Simmental x Hereford (S x H) and Friesian x Hereford (F x 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 x 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 x H (33%) requiring more assistance than F x H (15%) and S x H (10%) heifers, while B x H heifers did not require any assistance. Genotype differences in percentage of calves born and weaned were observed on low pastures only, where B x H (66% born, 65% weaned) exceeded H x H (48%, 39%) and S x H (39%, 38%) cows, with F x H (58%, 50%) cows being intermediate. Calves by H x 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 x H and S x H cows produced the fastest-growing calves on high quality pasture (966 and 936 g/day, respectively) while B x H cows produced the fastest-growing calves on medium (823 g/day) and low (679 g/day) quality pastures. F x H cows weaned the heaviest calves on high quality pasture (274 kg) while F x H and B x 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.