INCREASED POSTWEANING GAIN OF BEEF HEIFERS ENHANCES FERTILITY AND MILK-PRODUCTION

Four hundred fifty-two (452) weanling heifer calves (192+/-23 kg) were used to determine the effect of postweaning weight gain on subsequent reproductive performance and lactation. Heifers grazed stockpiled tal l fescue pastures and were fed a high (H) or low (L) amount of ground corn supplement (3.68 and 2.99 kg/[animal d], respectively) during a p ostweaning treatment period of 136 d. Postweaning gain of heifers rece iving L and H was .43 and .62 kg/d, respectively. These treatments res ulted in a range of postweaning gain from .07 to 1.17 kg/d. Heifers re ceiving H were 26 kg heavier (P < .01), had .15 cm more fat thickness (P < .01), 5% greater pelvic area (P < .01), and tended (P = .08) to h ave greater hip height than heifers receiving L at yearling. More heif ers in the H group were pubertal before the start of the breeding seas on (70.9 vs 61.3%) (P < .05). No Significant differences were found in pregnancy rate or first-service calving rate between treatment groups . Mean milk production was 10% greater for H- than for L-fed heifers ( P < .01) and resulted in heavier calves at 54, 104, and 153 d of age ( P < .05). Regression analysis revealed that as weaning weight and post weaning gain increased, so did the probability for reaching puberty be fore the breeding season. Increasing weaning weight also increased the probability of calving to the first AI service. As heifer weaning wei ght and postweaning gain increased, subsequent milk production also in creased. Increasing postweaning weight gain of lightweight heifers fro m .07 to 1.17 kg/d increased both reproductive and lactation performan ce.