Energy requirements for maintenance of crossbred beef cattle with different genetic potential for milk.

Maintenance energy requirements were estimated in two gestation and one lactation feeding trials for three groups of cows. All cows in the second gestation trial completed the first gestation and lactation trials. The three groups were chosen to represent cattle similar in growth rate and mature size but different in amount of milk provided to their calves. The low (L) group included Hereford x Angus, the medium (M) group included Red Poll x Angus and the high (H) group included Milking Shorthorn x Angus cows. Cows were individually fed to maintain net body weight (minus gravid uterus for gestation) constant. Allowances were made in energy intake for gestation and lactation. Cow weights were adjusted to an average condition score in each trial. Daily maintenance requirements during gestation were 18% lower than those during lactation. The H and M cows required 12% more energy per unit metabolic weight than L cows to maintain body weight during both gestation and lactation. Differences in milk production explained 23% of the variation in maintenance requirements, suggesting that important differences exist beyond those associated with milk production potential. Repeatabilities of maintenance requirement measurements ranged from .44 to .64. Maintenance requirements for calves under feedlot conditions in the postweaning phase were estimated from data collected from 494 calves, half-sibs and offspring of the cows described previously. Energy requirements were 11% higher for the H and M groups than for the L group.