Effect of postpartum bull exposure on calving interval of first-calf heifers bred by natural service

Abstract

Ninety-four first calf heifers were utilized to evaluate the effect of bull exposure on the calving interval. Heifers were alternately assigned after calving to a pasture containing epididymectomized bulls for 60 d or were not exposed. Thirty-five days prior to the breeding season the bulls were removed and the two groups co-mingled. Bull-exposed heifers had a 9-d increase in calving interval and a 7-d delay in average calving date compared to unexposed heifers (P < 0.05). Bull exposure early postpartum did not shorten the calving interval of heifers in condition score of 5 or better at calving and bred by natural service under the conditions of this study. Key words: Bull exposure, first-calf heifers, reproduction, calving interval, postpartum