Components of performance and biological efficiency of crossbred beef cattle with different genetic potential for milk

Three cow groups similar in growth and mature size but different in amount of milk provided to their calves (low (L) = Hereford x, medium (M) = Red Poll x and high (H) = Milking Shorthorn x Angus) were studied. Two gestation and one lactation trials were conducted to estimate maintenance energy requirements. 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. Variation in milk production explained 23% of the variation in maintenance requirements. Repeatabilities of mesurements ranged from.44 to.64. Maintenance requirements for calves under feedlot conditions in the postweaning phase were 11% higher for the H and M groups than those for the L group. Reproductive performance was not significantly affected by milk group under the pasture-feeding and management conditions in this study. Days to first postpartum estrus, calving date, pregnancy rate and calf-crop percentage were essentially the same. Average mature weights were 530, 476 and 503 kg for L, M and H cows, respectively. The highest weights were at weaning; the lowest were at calving (spring) for L and M cows and at the start of the breeding season for H cows. Biological efficiencies to weaning and slaughter were estimated as the ratio of estimated calf weight weaned or carcass weight produced by a 100-cow herd, to estimated metabolizable energy required by the cows and preweaning non-milk or preweaning non-milk and postweaning by the calves. Efficiencies to weaning were 28.1, 28.2 and 28.0 g/Mcal and to slaughter were 21.8, 20.8 and 20.0 g/Mcal for L, M and H cows, respectively