Effects of early and late fall calving of beef cows on reproduction and calf growth

Effects of early and late fall calving on gestation length, pregnancy rate, and weaning weight were evaluated in Angus x Hereford cows during 4 years. Sixty fall calving cows were blocked according to age and prior calving date, and allocated for insemination in late fall (Nov. 7-8) or winter (Jan. 4-7). Control of ovulation was accomplished with the Ovsynch protocol. All cows grazed native grass pastures and were fed supplemental protein in the winter to control body condition scores (BCS, 1=emaciated and 9=obese) such that cows maintained a BCS of at least 5 during breeding, 4 or greater at the end of winter supplementation, and greater than or equal to 6 at calving. The percentage of cows with ovarian function at the start of breeding and percentage of cows pregnant were not significantly different for the early and late calving seasons. Early fall born calves were exposed to higher ambient temperatures and had shorter gestation lengths ( P < 0.05) than late fall born calves. Early fall born calves had similar birth weights as late fall calves, however, weaning weights were greater (P < 0.01) for late fall born calves compared with early born calves. Similar feed requirements and reproductive performance for early and late fall calving cows, with greater weaning weights for late calving cows, indicates that late fall calving is more profitable in central Oklahoma.