SYNCHRONIZATION OF ESTRUS AND ARTIFICIAL INSEMINATION IN BEEF CATTLE

Fifty Aberdeen Angus cows were group-fed 1 kg of meal containing 10 mg of 6-chloro-Δ6-17 acetoxyprogesterone (CAP) per female per day for 14 days, followed by 1 kg of meal containing 5 mg of CAP per female per day for 4 days. Twenty-five cows were injected with 1,000 IU of human chorionic gonadotrophin (HCG) 48 hr after the last CAP feeding. The cows injected with HCG were artificially inseminated 12–24 hr after the injection. Non-injected cows were inseminated approximately 12 hr after the onset of standing heat. CAP was successful in suppressing estrus in 47 (94%) of the cows during the feeding period. Seven of the 20 non-injected cows which showed heat conceived to the first post-treatment service. Six of the 15 HCG-injected cows which showed heat and four of the 10 HCG-injected cows which did not show heat conceived to the first post-treatment service. Of the 27 cows which showed a second post-treatment estrus and were inseminated, 13 cows conceived, giving a total of 30 cows conceiving to the artificial insemination services. The HCG injection had no significant (P > 0.05) effect on the incidence of estrus or conception; however, it did eliminate the problem of detecting estrus and significantly (P < 0.01) reduced the time required for restraining and inseminating the cows.