Synchronization of oestrus and subsequent fertility in cattle, using the prostaglandin F₂α analogue, ICI 80996 (cloprostenol)

Abstract

The prostaglandin analogue, ICI 80996 (cloprostenol), was administered subcutaneously to synchronize oestrus in cattle. One injection, or two injections 12 days apart, of 400 pg gave optimal results (78 and 72 per cent synchronized respectively) for the Hereford cross heifers used. Heifers treated with cloprostenol from days one to five of the cycle, did not respond to the first injection, but did so to a second injection given 12 days later. A greater percentage of heifers, treated in the mid or late luteal phase of the cycle, exhibited oestrus after the first injection of cloprostenol than after the second injection. The percentage of these heifers showing induced oestrus varied from 44 to 100 per cent. There was a peak in the incidence of oestrus between 49 and 72 hours after injection but the distribution ranged from 24 to 120 hours. 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. However, about 30 per cent 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 second injection. Some of these heifers had abnormal progesterone profiles and subsequent reproductive patterns. Fertility, following one or two subcutaneous injections of cloprostenol and artificial insemination at the set times of 72 and 96 hours, was 30 and 46 per cent respectively. However, if only heifers inseminated at the optimum time were considered, fertility at pregnancy diagnosis (73 and 65 per cent) and calving (53 and 57 per cent) was acceptable.