Effects of Early Weaning Calves from First-Calf Heifers on Calf and Heifer Performance

Abstract

Sixty-three Angus × Hereford calves from first-calf heifers were assigned at birth to remain with their dams until weaning (NW) at 7 months or to be early weaned (EW). Calves were born between February 18 and April 17 and those assigned to be EW were weaned every 2 weeks at 6 to 8 weeks of age. EW calves were raised in drylot and self-fed high concentrate diets until July, when one-half of the calves were moved to pasture and creep-fed. Heifers with EW calves and heifers with NW calves were bled at weekly intervals between 6 and 13 weeks postpartum for plasma progesterone analysis. All heifers were exposed to Angus bulls from May 29 to July 31. NW calves weighed 169.3 kg, at 7 months of age, compared to 169.8 kg for EW calves. Moving calves to pasture with creep feed reduced (P>.05) gains of EW calves by 20 kilograms. Conception rate was greater (P>.05) among EW (96.8%) than among NW heifers (59.4%) during the 64-day breeding season. The average interval from parturition to conception was reduced (P>.05) from 90.5 to 73.0 days by early weaning. Ovarian activity, as indicated by progesterone levels greater than 1 ng/ml, was initiated by 85 days postpartum in 90.3% of the EW heifers, compared to 34.3% of the NW heifers (P>.005). EW heifers gained more rapidly (P>.05) during the summer.