Hormones are commonly used to manipulate the estrous cycle. The major indications for hormonal control of estrus are to induce luteolysis, induce ovulation of a mature follicle, suppress estrus, induce cyclicity in anestrous animals, and superovulate cyclic animals. Effective treatments for these manipulations of the estrous cycle vary between species. Additionally, a number of treatments currently lack regulatory approval; prescribing veterinarians should follow label instructions and adhere to relevant laws and regulations.
Hormonal control of estrus in horses, ruminants, and small animals is discussed in this section. For pigs, refer to Breeding Management in Pigs Breeding Management in Pigs Sows and gilts are nonseasonal and polyestrous, with the estrous cycle lasting 18–24 (average 21) days. Sows are behaviorally anestrous during pregnancy. Ovulatory estrus usually is not seen... read more .