Evaluation of Hereford and first-cross cows on three pasture systems .3. Milk yield and its influence on calf performance

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 x H) and first-cross Brahman x Hereford (B x H), Simmental x Hereford (S x H) and Friesian x Hereford (F x 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 preweaning 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 (R-2) between models for calf 210-day weight and ADGtotal which included average lactation milk yield and other cow traits (highest R-2 = 69 %) and models which included other cow traits but no milk yield estimate (highest R-2 = 57%) were < 13%. Cow breed rankings for average lactation milk yield were similar to those for calf 210-day weight and ADGtotal. On high quality pasture, S x H and F x H cows produced the most milk (S x H, 7.5 kg/day; F x H, 8.3 kg/day; B x H, 5.7 kg/day; H x H, 5.5 kg/day) and weaned the heaviest calves (S x H, 255 kg; F x H, 252 kg; B x H, 215 kg; H x H, 217 kg), while on low quality pasture, B x H and F x H cows produced the most milk (B x H, 4.2 kg/day; F x H, 3.7 kg/day; S x H, 2.9 kg/day; H x H, 2.7 kg/day) but B x H cows weaned the heaviest calves (B x H, 180 kg; F x H, 168 kg; S x H, 159 kg; H x H, 124 kg).