Abstract
A STUDY was made of the effect of relative first calving date in beef heifers on lifetime production using production records records from two beef herds. The study involved 2036 spring calves from 481 cows weaned in October or November of each year. An initial calving group was determined for each heifer based on the relative birth date of her first calf. A subsequent calving group was similarly assigned to each additional calf from the same cow. Heifers calving initially in the Early, first and second groups tended to calve earlier throughout the remainder of their productive lives than heifers calving initially in later groups. However, repeatability estimates for calving group in the two herds were 0.092 and 0.105 indicating that only moderate improvement might be made by culling cows that calve late during the normal calving season. Calves born in earlier groups grew significantly faster from birth to weaning and weighed more at weaning than calves born in later groups. Lifetime production was significantly affected by initial calving group. Early calving heifers had higher average annual lifetime calf production than late calving heifers. This study indicates the importance of managing and breeding heifers so they will calve early in the season and thus tend to maintain early calving throughout their productive lives. Such management should contribute profit in the cow-calf operation. Copyright © 1973. American Society of Animal Science . Copyright 1973 by American Society of Animal Science.