On-farm monitoring of mating performance of single yearling Hereford bulls

Abstract

The reproductive performance of 18 yearling Hereford bulls was monitored in detail to relate mating marks (from chinball harnesses) to subsequent pregnancy and calving results and calving dates. Single-sire mating groups with Hereford yearling heifers and cows at pasture (average 27 females per group) were monitored over 8 – 10-week mating periods in the springs of 1983 – 85. The herd was of interest because of a suspected problem with bull fertility. Over the 3 years, 520,10 of females put to the bull were marked in the first 3 weeks; 36% of those put to the bull calved in the first 3 weeks of calving. Over the whole calving period, 71 % of females calved, including those put to five bulls of low reproductive performance. Two of these were identified during mating, one with few mating marks (first 3 weeks) and one with a high return rate (Weeks 4 – 5). However, under the commercial beef farming conditions prevailing, the other three were not identified until pregnancy diagnosis. There was greater variation in reproductive performance among yearling bulls within a year than among years. About one-fifth of each mating group consisted of yearling heifers, which had been monitored for puberty using vasectomised bulls before the entire matings began. More heifers (+ 21 %) subsequently became pregnant to entire bulls in the 8-week mating period if heifers had reached puberty by the start of mating than if they had not.