Serving Activity of a Beef Bull to Heifers in which Estrus was Synchronized

Sexual behavior and reproductive efficiency of Nihon Tankaku (Japanese Shorthorn)bull to ll heifers were examined in a 10m×15m free barn, where they were housed for 48 hr during the winter of 1977. Ten of the heifers had been injected with PGF2α analogue 43 hr before the observation started. Estrous behaviour appeared definitely in 7 of the treated heifers during a period from 43 to 91 hr after PGF2α injection. Onsets of estrus were not observed at any particular time during the aeriod. The bull mounted 4 to 20 times(89 in total)and ejaculated 3 to 8 times (29 in tota1)for 7 estrous heifers which comprised 6 PGF2α-treated and l non-treated ones. The bull showed serving activity to 6 of the estrous heifers in order. As a result of the trial, 7 of 8 estrous heifers were conceived by housing with a bull for 48 hr.