Synchronization of Estrus in Goats

Estrous cycle synchronization can be performed in several ways, depending on the time of year and the relationship to the doe’s natural breeding season. Out-of-season breeding is of interest to dairy goat owners, because it reduces seasonal fluctuation in the herd’s milk production. In meat production systems, increased conception rates and litter sizes are important, and breeding can be manipulated using nutritional and hormonal therapies.

Sudden introduction of an odoriferous buck in the transitional period (the Male Effect) often advances the onset of cycling in does by a few weeks, and the does also may show some synchronization. The buck should be housed out of sight, smell, and hearing range from the does for ≥ 3 weeks before introduction for this technique to be effective. Even if the whole group does not cycle, this method can enable a few does to conceive earlier in the season.

Methods to artificially induce cycling in does have been developed to mimic the short-day conditions during the breeding season. Melatonin, which is secreted by the pineal gland during periods of decreasing day length, helps bring goats into season. Decreasing exposure to artificial lights may cause does to begin secreting more melatonin and start cycling. However, it may take weeks for this method to take effect, and does must be exposed to long days first to prevent them from becoming photorefractory.

Exogenous melatonin may also be administered alone or in conjunction with lighting protocols to produce short-day effects and induce breeding activity in both does and bucks. However, no melatonin sources are currently approved for use in goats in the US.

The Animal Medicinal Drug Use Clarification Act (AMDUCA) of 1994 places limits on extralabel drug usage in food-producing animals in the US and restricts extralabel use to animals that are suffering or in danger of death (1). Under AMDUCA, pharmaceuticals cannot be used extralabel to alter reproduction for production purposes.

The Medicinal Uses in Minor Species (MUMS) Act of 2004 helps expedite use of certain drugs and allows pharmaceutical companies to acquire conditional approval for their use in minor species, such as goats (2). Controlled intravaginal drug-releasing (CIDR) devices labeled for sheep are being considered for conditional approval in goats under MUMS, although, if approved, a valid veterinary-client-patient relationship will be a requirement.

The following comments about manipulating reproduction are provided for informational purposes and for use in countries outside the US.

In does with a functional corpus luteum, administration of a synthetic PGF_2α analogue (dinoprost tromethamine 7.5 mg, IM, once) will cause luteolysis and bring does into heat in about 2–5 days (3). This method is not effective during anestrus because of the absence of ovulation and corpus luteum formation (4).

For cyclic does, a common synchronization protocol is to administer two doses of PGF_2α 10 days apart, followed by heat checking and breeding by the AM:PM rule for 7 days (5).

Another synchronization method has been developed by researchers at North Carolina State University to perform timed artificial insemination (AI) in cycling does (5). This method begins with administration of PGF_2α (day 0), followed by administration of a GnRH agonist 7 days later (day 7), administration of another dose of PGF_2α 7 days later (day 14), and administration of the GnRH agonist and AI 72 hours later (day 17). The author has used this protocol with much success and will sometimes modify it to include placing a CIDR insert at the same time as GnRH agonist administration and removing it at the second PGF_2α dose.

Progestagen treatment can be administered to synchronize does either within or outside the breeding season. It can be administered in the form of injections with an oily base every 3 days, impregnated vaginal sponges (eg, flurogestone acetate or methyl acetoxyprogesterone, also known as medroxyprogesterone acetate or MPA), norgestomet implants, oral administration of melengestrol acetate, or CIDR intravaginal inserts.

Progestagen devices may be applied using short (approximately 5 days) or long (approximately 14 days) protocols. Because of declining progesterone concentrations when CIDRs are in place for > 7 days, short-day protocols are commonly preferred, though longer protocols tend to be preferred for out-of-season breeding.

A dose of PGF_2α is recommended when initiating a short protocol (ie, at CIDR insertion), to ensure no corpus luteum is present at the time of CIDR removal. When using long CIDR protocols, PGF_2α may be administered 24–48 hours before CIDR removal or completely omitted, because the corpus luteum lifespan should be exceeded by the time of removal.

After progestagen treatment, administration of a GnRH agonist (gonadorelin 100-125 mcg, IM, once), follicle-stimulating hormone (FSH) (55–200 mg, IM, once), or pregnant mare serum gonadotropin (PMSG) (200–750 IU, IM, once) will promote the onset of estrus activity (4, 6). A commercially available product marketed for use in swine that contains both PMSG and human chorionic gonadotropin is also commonly administered at the end of progestagen treatment.

Both FSH and PMSG have a superovulatory effect and can be used to increase ovulation rate and litter size in does. Good conception rates can be achieved with this system when used within or outside the breeding season, and it allows for fixed-time insemination.