Abstract
Lactating Hereford and Hereford ✕ Angus cows, 2 to 6 yr old, and their calves were used in two trials to study the effects of energy intake on the postpartum interval (PPI) and the adequacy of the cow's milk production for calf growth. In trial 1, 23 cows were fed either 120 (high energy, HE) or 100% (adequate energy, AE) of National Research Council energy recommendations. Cow weights, calf weights and milk production were determined 1 wk after calving and every 2 wk until 17 wk postcalving. One half of the calves received creep feed from the start of the study, whereas the other half did not receive creep feed until their average daily gain was below .23 kg/d. In trail 2, 19 cows were fed energy levels of 100 (AE) or 85% (low energy, LE). Estimated percentage body fat (EPBF) was estimated twice during the study; other variables were determined as in trial 1. In trial 1, the HE cows gained more weight (P<.01) and produced more milk (P<.01). In trial 2, the AE cows gained more weight (P<.01) and produced calves 17 kg heavier (P<.01) at the end of the study than did the LE cows. Milk production was not influenced by energy treatment (P>.2). It required 7.5 kg of milk and 2.3 kg of creep feed to produce 1 kg of calf gain in trial 1. By wk 9 of lactation, milk production was not adequately supporting calf growth; however, creep feed intake was able to compensate and rapid calf growth was maintained. Increasing milk production extended the PPI whereas increasing energy intake and EPBF shortened the PPI. A multiple regression including the linear and quadratic effects of energy intake and EPBF accounted for 71% (P<.01) of the variation in PPI. Copyright © 1984. American Society of Animal Science. Copyright 1984 by American Society of Animal Science.