Effects of feeding energy or protein supplements before or after calving on performance of spring-calving cows grazing native range.

In three consecutive years, spring-calving Hereford and Hereford x Angus cows (n = 348) were used to determine effects of level of supplemental energy or protein before and after calving on cowherd performance. Beginning on November 1, cows were individually fed 1.22 kg/d of a 40% CP (PROTEIN) or 2.44 kg/d of a 20% CP supplement (ENERGY) until calving. After calving, cows remained on the same supplement, were switched to the other supplement, or were fed 2.44 kg/d of a 40% CP supplement (HI PROT). Supplementation ended on April 20, the start of a 65-d breeding season. Cows fed ENERGY during gestation had greater BW gains (9 kg) at calving than PROTEIN-fed cows (P < .01). Calf weaning weight was not affected by supplementation. Cows fed ENERGY before calving had an 11% greater pregnancy rate than the cows fed PROTEIN (P < .002). Cows fed PROTEIN or ENERGY after calving had similar BW gains but cows fed HI PROT after calving lost less BW during supplementation (P < .002). Pregnancy rates were not influenced by treatments fed for a short period after calving. In conclusion, conception rates were significantly improved by feeding greater levels of supplemental energy prepartum but not postpartum. Energy supplements can affect reproduction with minimal effects on BW or condition.