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, increasing conception rates and litter sizes are important and can be manipulated using nutritional and hormone therapies.
The sudden introduction of an odoriferous buck in the transitional period often advances the onset of cycling by a few weeks, and the does also may show some synchronization. The buck should be housed out of sight and smell from the does for ≥3 weeks before introduction. 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 to bring goats into season. Decreasing exposure to artificial lights may cause does to begin secreting more melatonin and start cycling. 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 extra-label drug usage in food-producing animals in the US and restricts extra-label use to animals that are suffering or in danger of death. Under AMDUCA, pharmaceuticals cannot be used extra-label 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. Currently, controlled intravaginal drug-releasing 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 PGF2alpha analogue will cause luteolysis and bring does into heat in about 2–5 days. This method is not effective during anestrus because of the absence of ovulation and corpus luteum formation. For cyclic does, a common synchronization protocol is to administer two doses of PGF2alpha 10 days apart, followed by heat checking and breeding by the AM:PM rule for 7 days. Another synchronization method ( NC Synch) has been developed by researchers at North Carolina State University to perform timed artificial insemination (AI) in cycling does. This method begins with administration of PGF2alpha (day 0), followed by administration of a GnRH agonist 7 days later (day 7), administration of another dose of PGF2alpha 7 days later (day 14), and administration of the GnRH agonist and AI 72 hours later (day 17).
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), norgestomet implants, oral administration of melengestrol acetate, or CIDRs. Progestagen devices may be applied using short (~5 days) or long (~14 days) protocols. Because of declining progesterone concentrations when CIDRs are in place for >7 days, short-day protocols are becoming more popular. A dose of PGF2alpha is recommended when initiating a short protocol (ie, at CIDR insertion), to ensure no corpus luteum is present at CIDR removal. When using long CIDR protocols, PGF2alphamay 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 either a GnRH agonist, follicle-stimulating hormone (FSH), or pregnant mare serum gonadotropin (PMSG) will promote the onset of estrus activity. A commercial product marketed for use in swine containing both PMSG and human chorionic gonadotropin is also commonly administered at the end of progestagen treatment. Both FSH and PMSG have a super-ovulatory effect and can be used to increase ovulation rate and litter size. Good conception rates can be achieved with this system when used within or outside the breeding season, and it allows for fixed-time insemination.