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 of Pigs Domesticated sows and gilts are classified as nonseasonal and polyestrous, with the estrous cycle lasting 18–24 (average 21) days. However, pigs do show seasonal declines in fertility associated... read more .