Hormones are commonly used to manipulate the estrous cycle in animals. 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, or superovulate cyclic animals. Effective treatments for these manipulations of the estrous cycle vary between species, especially in animals that are seasonally regulated.
Of the common domestic species, horses and cats are long-day seasonally polyestrous breeders that experience periods of estrus during times of extended daylight in a given geographical location. In contrast, small ruminants are short-day polyestrous breeders; and cows, pigs, and dogs experience no seasonal impacts (see the table ).
Characteristics of the Estrous Cyclea in Common Domestic Species
Species | Seasonality | Cycle Type | Ovulation Control | Average Length of Estrous Cycle (Range) |
|---|---|---|---|---|
Horsesb | Long-day seasonal breeders | Polyestrous | Spontaneous ovulators | 21 d (18–24 d) |
Cattlec | Nonseasonal breeders (continuous) | Polyestrous | Spontaneous ovulators | 21 d (18–24 d) |
Sheepd | Short-day seasonal breeders | Polyestrous | Spontaneous ovulators | 17 d (14–20 d) |
Goatsd | Short-day seasonal breeders | Polyestrous | Spontaneous ovulators | 21 d (18–24 d) |
Dogse | Nonseasonal breeders | Monoestrous | Spontaneous ovulators | 6–10 mo (varies widely) |
Catsf | Long-day seasonal breeders | Polyestrous | Primarily induced ovulators; spontaneous ovulation possible | 14–21 d (varies by breed and breeding status) |
a See the table . b Moss C, Lu K. Hormonal manipulation of the estrous cycle in mares. Clin Theriogenology. 2025;17(special issue):49-63. doi:10.58292/CT.v17.11651 c Kasimanickam R, Harting Q, Hanson R, Boler R. Estrus and ovulation synchronization strategies in beef cattle. Clin Theriogenology. 2025;17(special issue):9-23. doi:10.58292/CT.v17.11650 d Waqas MS, Tibary A. Manipulation of ovarian function in sheep and goats. Clin Theriogenology. 2025;17(special issue):24-35. doi:10.58292/CT.v17.11653 e McRae G, Runcan E, Johnson A. Estrous cycle manipulation in dogs. Clin Theriogenology. 2025(special issue);17:82-86. doi:10.58292/CT.v17.11647 f Barnes J, Vansandt L. Estrous cycle manipulation in cats. Clin Theriogenology. 2025(special issue);17:67-81. doi:10.58292/CT.v17.11649 | ||||
Stages of the estrous cycle commonly include the follicular phase under estrogen dominance and the luteal phase under progesterone dominance; however, the individual designation (proestrus, estrus, metestrus, diestrus) and progression vary substantially between species. In addition, a number of treatments currently lack regulatory approval; prescribing veterinarians should follow label instructions and adhere to relevant laws and regulations.
Hormonal control of the estrous cycle in horses, ruminants, and small animals is discussed in this chapter. For pigs, refer to Breeding Management in Pigs.
