Estrus can be induced 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 hormone therapy.
The sudden introduction of an odoriferous buck often advances the onset of cycling by a few weeks, and the does also may show some synchronization. The buck should be housed well away from the does (out of their sight and smell) for ≥3 wk before introduction. Even if the whole group does not cycle, this method can get a few to conceive in the theoretically out-of-season period.
Providing 20 hr of light per day in January and February (northern USA), with a sudden return to available daylight on March 1, will bring goats into estrus several weeks later. In this system, it is more difficult for the owner to pick out the does that are in estrus; consequently, running a young, vigorous buck with the does gives the highest conception rate. If a portion of the herd is artificially synchronized, some of the remaining does also may come into estrus.
The Animal Medicinal Drug Use Clarification Act of 1994 (AMDUCA) places limits on extra-label drug usage in food-producing animals in the USA and restricts extra-label use to animals that are suffering or in danger of death. Under AMDUCA, pharmaceuticals cannot be used to alter reproduction for production purposes, and the following comments about manipulating reproduction are provided for use in countries outside the USA.
If the corpus luteum is functional, a synthetic PGF2α analogue will induce estrus; however, this is not effective during anestrus. Additionally, it may provoke short cycles that tend to be seen normally at the beginning of the season. Melatonin implants may also be used to produce short-day effects and induce sexual activity in both does and bucks.
Progestagen treatment, followed by administration of FSH or pregnant mare serum gonadotropin (PMSG), will cause out-of-season estrous activity. Good conception rates can be achieved with this system, and fixed-time insemination is feasible, but these products (FSH and PMSG) are not approved for use in goats. Progestagen treatment can be 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 a controlled intravaginal drug-releasing device, or CIDR (which is a form of progestagen-impregnated silastic for vaginal use). A commercial product marketed for use in swine containing both PMSG and human chorionic gonadotropin will also cause does to cycle outside the normal breeding season when administered at the end of progestagen treatment.