Synchronization of estrus following 7 or 9 day treatment with chlormadinone acetate (CAP)

Abstract

Synchronization of estrus and fertility were determined in a series of 8 trials. Various levels of chlormadinone acetate (CAP) were fed for either 7 or 9 days. An injection of 5 mg of estradiol valerate and CAP was given at the start of the feeding period. In some trials estradiol 17β was injected near the end of the feeding period. In trial 1, 98% of the CAP-treated heifers were in estrus in a 5-day period, but only 46% conceived at first service compared to 80% in the non-synchronized heifers (P<.01). In trials 2 through 6, 0.25 mg estradiol 17β injected either 60 or 72 hours after the last CAP feeding reduced the interval to ovulation in heifers that ovulated. However, use of estradiol 17β reduced the number of heifers ovulating in most trials. In trials 7 and 8, estrus was effectively synchronized with either 7- or 9-day feeding of 7.5 or 10 mg of CAP daily followed by .5 mg estradiol 17β, 72 hours after the last CAP feeding. Pregnancy rates at first service varied from 21 to 45% in heifers in the synchronized groups, compared to 58% in the controls in trial 7 (P<.05). In trial 8 pregnancy rates at 1st service varied from 29 to 47% in treated heifers compared to 72% in controls (P<.01). In this series of trials, fertility was reduced from 24 to 43% with the use of CAP and estradiol valerate. Conception rates at first service were not improved by varying the length of feeding (7 or 9 days), level of CAP (7.5 or 10 mg) or by attempting to reduce the variation in ovulation time with estradiol 17β. None of the combinations of these three drugs used increased fertility in these trials.