Current concepts in synchronization of estrus: Sheep and goats

Estrus synchronization (ES) in goats and sheep is achieved by control of the luteal phase of the estrous cycle, either by providing exogenous progesterone or by inducing premature luteolysis. The latter approach is not applicable during seasonal anestrus, whereas exogenous progesterone in combination with gonadotropin can be used to induce and synchronize estrus in anovular does and ewes. In the United States, ES in small ruminants is limited by the availability of appropriate pharmaceuticals, and there is a need for use of products designed and approved for the major livestock species (cattle and swine). The traditional product of choice for ES in goats and sheep is the intravaginal sponge impregnated with progestagen (e.g., flurogestone acetate or methyl acetoxyprogesterone) for 9 to 19 d followed by PMSG injected -48 to 0 h from sponge removal. Alternative choices of progesterone/progestagen have been controlled internal drug release (CIDR) devices, supplying natural progesterone, norgestomet implants, and orally active melengestrol acetate. Other products used alone or in conjunction with progestagens are PGF2α or an analogue (cloprostenol), a combination of PMSG/hCG, and zeranol. This review summarizes some of the research efforts in the 1990s to establish optimal dose levels and timing of administration, particularly for extra-label use products, achieve tighter synchrony in support of timed insemination, and use the male effect and short-term nutritional manipulation in nonpharmacological approaches to induce ovulation and enhance ovulation rate.