Estrogen
The hormone estradiol has limited use in equine reproduction. It can be used to cause estrous behavior in a non-cycling or ovarectomized mare. Estradiol cyprionate, 5-10 mg daily for 1 week, will induce estrous behavior if there is no CL (no progesterone). This approach is often used to create a mare that will be in estrus and used to tease stallion on which semen collection is desired.
Estradiol 17-B (1-2 mg given 24 hr before breeding) will induce estrous behavior in mares with a follicle (35-45 mm) if the mare does not exhibit estrous behavior on her own. The estradiol 17-B will also trigger increased LH to cause ovulation. In some problem mares that do not exhibit estrus, this approach is used to induce estrus behavior and ovulation when a follicle is detected and natural service is desired.
