Effects of postweaning rate of gain on onset of puberty and productive performance of heifers of different breeds.

Angus, (n = 78), Hereford (93), Red Poll (61), Brown Swiss (47), Charolais (36) and Simmental (90) heifers were used in a study designed to evaluate the effects of breed and postweaning rate of gain (low, L = .4 kg/d; medium, M = .6 kg/d; high, Hi = .8 kg/d) on the onset of puberty and subsequent maternal performance. After a 184 d feeding period, one-half of the heifers in each group were moved to pasture and one-half were kept in the feedlot through breeding (70 d), then moved to pasture. Breeds differed (P less than .01) in weight, height and condition. Increased postweaning rates of gain resulted in increased heifer weight (P less than .01), height (P less than .10) and condition (P less than .01) before calving (198 to 635 d) but these differences were not observed after rebreeding (930 d). Quadratic regressions of percentage pubertal vs age were significantly influenced by the interaction between breed and postweaning rate of gain. Both mean age and weight at puberty were influenced by breed (P less than .01) and postweaning rate of gain (P less than .01). No interactions were observed (P greater than .10). Calf birth weight was influenced (P less than .01) only by breed. Milk production was influenced by breed (P less than .01) and postweaning rate of gain (P less than .10). Significant time after parturition and time X breed interaction effects on milk production were observed. Calf weight at 120 d and at weaning was influenced by breed (P less than .01), heifer postweaning rate of gain (P less than .05) and sex (P less than .05). These data suggest moderate underfeeding or overfeeding during the postweaning period may have a prolonged influence on the productive performance of heifers and demonstrate that breeds differ widely in age at puberty and later productivity under the type of management and environment of this study.