Service Sire Influences on Fertility Rates of Repeat Breedings

Abstract

Data from 6232 inseminations with semen of 39 bulls by 1 man in one area of Washington from Aug., 1949 through Oct., 1951 were used for this study. No important breed differences with respect to 180-day nonreturn rates or avg. repeat service intervals were present. High fertility bulls showed a 180-day nonreturn 1st service rate of 70% compared with 63 and 59%, respectively, for medium and low fertility bulls. The fertility level of the bull had a marked effect on the fertility of repeat services with semen from other bulls. Low fertility bulls were 17% below their 1st service avg. when bred to repeats of low fertility bulls, but only 4-5% lower when bred to medium and high fertility bulls. The fertility of repeat services by high fertility bulls was -1, -4, and -7%, respectively, when they followed bulls of high, medium, and low fertility.