SYNCHRONIZATION OF ESTRUS AND SUBSEQUENT FERTILITY IN CATTLE, USING PROSTAGLANDIN-F2ALPHA ANALOG, ICI 80996 (CLOPROSTENOL)

The prostaglandin analog, ICI 80996 (cloprostenol), was administered s.c. to synchronize estrus in cattle. One injection, or 2 injections 12 days apart, of 400 .mu.g gave optimal results (78 and 72% synchronized, respectively) for the Hereford cross heifers used. Heifers treated with cloprostenol from days 1-5 of the cycle, did not respond to the 1st injection, but did so to a 2nd injection given 12 days later. A greater percentage of heifers, treated in the mid or late luteal phase of the cycle, exhibited estrus after the 1st injection of cloprostenol rather than after the 2nd injection. The percentage of these heifers showing induced estrus varied from 44-100%. There was a peak in the incidence of estrus between 49-72 h after injection but the distribution ranged from 24-120 h. Peripheral blood progesterone concentrations, palpation of the ovaries and subsequent cycle lengths, indicated that the cloprostenol had no adverse effects in the majority of heifers. About 30% of the heifers that responded to an initial injection of cloprostenol given in the mid luteal phase of the cycle failed to respond to a 2nd injection. Some of these heifers had abnormal progesterone profiles and subsequent reproductive patterns. Fertility, following 1 or 2 subcutaneous injections of cloprostenol and artificial insemination at the set times of 72 and 96 h, was 30 and 46%, respectively. If only heifers inseminated at the optimum time were considered, fertility at pregnancy diagnosis (73 and 65%) and calving (53 and 57%) was acceptable.