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 tall 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 postweaning treatment period of 136 d. Postweaning gain of heifers receiving L and H was .43 and .62 kg/d, respectively. These treatments resulted in a range of postweaning gain from .07 to 1.17 kg/d. Heifers receiving 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 have greater hip height than heifers receiving L at yearling. More heifers in the H group were pubertal before the start of the breeding season (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 postweaning gain increased, so did the probability for reaching puberty before the breeding season. Increasing weaning weight also increased the probability of calving to the first AI service. As heifer weaning weight and postweaning gain increased, subsequent milk production also increased. Increasing postweaning weight gain of lightweight heifers from .07 to 1.17 kg/d increased both reproductive and lactation performance.