Supplemental Feed Protein Concentration and Weaning Age Affects Replacement Beef Heifer Performance

Sixty-four Simmental heifer calves were utilized in a 2 × 2 factorial treatment arrangement designed to determine the effects of weaning age and supplemental feed CP concentration on performance, reproduction, and milk production of heifer calves reared as replacements. Weaning occurred at an average of 89 ± 1.6 d of age (early weaning; EW) or 232 ± 1.8 d of age (normal weaning; NW); supplemental diets were either 12 or 17% CP. A weaning age × supplemental feed interaction (P<0.01) was observed for calf performance. Providing EW heifers additional CP improved (P=0.03) ADG; however, additional CP decreased (P=0.003) ADG in NW heifers. Normal-weaned heifers provided a 12% CP supplement had greater (P=0.001) ADG than did EW heifers; however, weaning age did not influence (P=0.20) ADG of heifers consuming a 17% CP supplement. Supplemental DMI was greater (P<0.001) for EW heifers. Early-weaned heifer BW was lesser (P≤0.08) through breeding. Despite lesser BW, more (P=0.05) EW heifers (81.3%) were pubertal at 8 mo of age than NW heifers (59.4%). By 83 d postpartum, no BW differences were observed (P=0.56) relative to weaning age. Diet did not influence puberty onset or postweaning BW (P≥0.30). Neither dam weaning age nor previous supplemental CP concentration influenced (P>0.15) first or second lactation milk production and calf performance. The influence of supplemental feed CP concentration on heifer performance is dependent on weaning age; however, reproduction and milk production were not affected. Early weaning reduced heifer BW until breeding and increased percentage of pubertal replacements at an early age without influencing milk production.