In general, small ruminants are seasonally polyestrous breeders. Sexual activity is affected by daylight (it starts when the daylight is shorter). In the tropics, reproductive activity is unaffected by seasonal variations. During the breeding season, in healthy nonpregnant females, ewes have an estrous cycle every 16–17 days (range 14–17 days), and does exhibit estrous cycles every 20–21 days (range 18–24 days).
The length of estrus in each species varies and might vary further with season, breed, age, and male presence. On average, estrus lasts 36 hours in both sheep (range 24–36 hours) and does (range 24–48 hours).
Protocols of estrus synchronization or induction in sheep and goats depend on when they are used: breeding season, transitional period, or nonbreeding season. As with cattle, similar protocols for estrus synchronization and superovulation may be considered, with small variations to increase conception rate and litter size. Likewise, many drugs discussed are considered as extralabel use in the US and are used more commonly outside of the US.
Estrus Synchronization in Goats and Sheep
During the breeding season in cycling goats, luteolysis can be induced by administration of prostaglandin F2alpha (PGF2alpha; 2.5–5 mg, IM, once [1]) or cloprostenol (75–150 mcg, IM [2]) as early as day 3 of the estrous cycle (estrus is day 0) in both sheep and goats. In sheep, PGF2alpha (3) or cloprostenol is effective after day 5 following ovulation.
Estrus can be synchronized in sheep and goats by the administration of two doses of prostaglandin, 11–13 days apart in does or 7–9 days apart in ewes (4). Other common ovulation synchronization protocols akin to those described above include the NCSynch method (5), in which two doses of prostaglandin are administered 14 days apart (on days 0 and 14). In addition, GnRH (4.2 mg, IM) is administered on day 7 and again on day 17 to stimulate ovulation (6, 7).
Estrus can also be synchronized in cyclic does and ewes by the administration of progestogens via intravaginal, implant, oral, or parenteral means. Intravaginal sponges impregnated with progestogens (medroxyprogesterone acetate or fluorogestone acetate) have been the most widely used agents for ovulation control; however, they are not available for clinical use in the US.
Progestogen treatment to control ovulation in sheep and goats is administered for 10–14 days in ewes and 14–21 days in does (2, 6). Shorter duration of progestogen treatment requires a luteolytic drug (eg, PGF2alpha) administered parenterally at the end of treatment.
In small ruminants, a controlled internal drug release (CIDR) intravaginal plastic device impregnated with progesterone (300 mg) can also be used for controlling ovulation (6). In the US, CIDRs are currently labeled for use in sheep and considered as extralabel use in goats.
The CIDR is maintained in the vagina for 7 days, and a luteolytic dose of PGF2alpha is administered 1 day before or at device removal. The administration of GnRH at the time of CIDR insertion has also been shown to be effective (2). The estrus response is high, occurring within 48–96 hours (2).
In regimens involving treatments other than prostaglandin alone, fertility might be decreased on the first estrus after treatment in ewes but not in does. During the transitional and nonbreeding seasons, melatonin implants (18 mg) induce fertile estrus 50–70 days after implant insertion (8).
Better estrus induction results are obtained when a melatonin implant is inserted late in the nonbreeding season or during the transitional period. The implant is biodegradable and does not need to be removed.
Estrus synchronization in small ruminants can be improved by the use of an estrus synchronization protocol at the end of implant action. During the nonbreeding season, a source of gonadotropin is required. Outside of the US, the most commonly used gonadotropin is equine chorionic gonadotropin (eCG), administered at the end of progestogen treatment (or 24 hours before device removal).
The eCG dose for goats and sheep depends on the season, breed, age, and postpartum interval, among other factors, and has been reported to range between 200 and 750 IU, IM, once (2, 6). A high eCG dose is characterized by superovulation, low fertility, shortened estrous cycles, pregnancy loss, and future gestational problems with multiple lambs or kids, such as pregnancy toxemia (6). Repetitive use of eCG has produced antibodies against eCG in certain sheep and goats, resulting in modification of the time of ovulation and consequent decrease of fertility when artificial insemination at a fixed time is done (6, 9, 10).
Within the US, extralabel gonadotropin treatment combining eCG (80 IU/mL) and human chorionic gonadotropin (40 IU/mL) (hCG), marketed for used in pigs and administered at the end of the progestogen treatment (2–3.5 mL, IM, once [11]), has been successful in small ruminants during the transitional period.
In addition to inducing out-of-season cyclicity, the eCG-hCG protocol, together with FSH, has superovulatory effects, increasing ovulation rates and potential litter size. It also enables fixed-time artificial insemination programs for the breeding of large groups of animals or for purposes of advanced reproductive techniques, such as embryo transfer.
For More Information
Waqas MS, Tibary A. Manipulation of ovarian function in sheep and goats. Clin Theriogenology. 2025;17(special issue):24-35.
Wildeus S. Current concepts in synchronization of estrus: sheep and goats. J Anim Sci. 2000;77(suppl E):1-14.
Pugh DG, Baird AN, Edmondson MA, Passler T, eds. Sheep, Goat, and Cervid Medicine. 3rd ed. Elsevier; 2021.
References
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Tibary A, El Allali K. Manipulation of the estrous cycle in sheep and goats. In: Tibary A, El Allali K, eds. Small Ruminant Theriogenology. John Wiley & Sons; 2026:313-321. doi:10.1002/9781394309832.ch19
Hackett AJ, Robertson HA. Effect of dose and time of injection of prostaglandin F2α in cycling ewes. Theriogenology. 1980;13(5):347-351. doi:10.1016/0093-691X(80)90046-1
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Waqas MS, Tibary A. Manipulation of ovarian function in sheep and goats. Clin Theriogenology. 2025;17(special issue):24-35. doi:10.58292/CT.v17.11653
Mirzaei A, Mohebbi-Fani M, Omidi A, et al. Progesterone concentration and lambing rate of Karakul ewes treated with prostaglandin and GnRH combined with the ram effect during breeding and non-breeding seasons. Theriogenology. 2017;100:120-125. doi:10.1016/j.theriogenology.2017.06.005
Abecia JA, Forcada F, González-Bulnes A. Hormonal control of reproduction in small ruminants. Anim Reprod Sci. 2012;130:173-179. doi:10.1016/j.anireprosci.2012.01.011
Roy F, Combes B, Vaiman D, et al. Humoral immune response to equine chorionic gonadotropin in ewes: association with major histocompatibility complex and interference with subsequent fertility. Biol Reprod. 1999;61(1):209-218. doi:10.1095/biolreprod61.1.209
Roy F, Maurel MC, Combes B, et al. The negative effect of repeated equine chorionic gonadotropin treatment on subsequent fertility in Alpine goats is due to a humoral immune response involving the major histocompatibility complex. Biol Reprod. 1999;60(4):805-813. doi:10.1095/biolreprod60.4.805
Cross LJ, Cross RM, Stormshak F. Optimal dose of PG600 when given to progestogen-synchronized ewes during anestrus as affected by day of the year and temperature. Transl Anim Sci. 2018;3(1):433-442. doi:10.1093/tas/txy092
