Regumate for Horses

Last Updated on February 22, 2022 by Allison Price

Regumate is a generic name for altrenogest, a synthetic hormone. Regumate is the only medication that has been proven to exhibit progesterone-type biologic activities in horses. Regumate is used in the clinical management of transition periods, heat suppression in performance mares, and maintenance of pregnancy in trouble mares.


Mares with limited ovarian development have little to no heat and are not susceptible to estrus. Follicle growth is triggered by longer days and begins in late winter or early spring. There are several waves of follicles in a mare that can grow and regress, and they do not ovulate during the transition between winter anestrus or the physiologic breeding period. Transitional Mares may have irregular or prolonged periods of sexual receptivity with each follicular cycle.

Regumate therapy is used during transition to reduce long periods of erratic estrous periods, and advance the first ovulation. Treatment is more effective in the transition period (i.e. After the middle of March, treatment is more effective than during the transition period. It is recommended that you have a 14 to 18-day treatment.

How closely should you monitor your mare’s heat cycle. Hormone therapy may be necessary to prepare your broodmare for breeding season. You can find all the information you need to prepare for breeding season in the free report by AQHA, Mare Care: Breeding Tips.

Regumate for Horses

Behavior Suppression

Mares in heat can be difficult to train and/or not perform to their full potential. It might be beneficial to suppress estrous behavior during performance or critical training sessions. Regumate is the most common hormone prescribed to suppress estrus in mares. The treatment should be started at least three days before the event or show and continued every day to maintain estrous suppression. Regumate can be used for a longer time period without any adverse effects on fertility or reproductive performance.

Ovulation Control

An embryo-transfer program might require synchronization of the ovulations from a donor mare and a recipient mare. It might also be necessary to modify or manipulate the estrous cycles of a mare in order to schedule breeding. Both of these tasks can be accomplished by regumate. Progestin is given once daily for 10-14 days. A dose of prostaglandins can be administered on the last day. After treatment is completed, mares can return to heat within three to five days. They can usually be bred within seven to nine days.

Pregnancy Maintenance

The corpus Lutum produces progesterone, which is necessary for maintaining pregnancy in the first two to three months. The placenta assumes the progesterone-producing role after 90 days. Some mares may experience early embryonic death due to insufficient progesterone production by the corpus. Mares who have had repeated early pregnancy losses are often advised to supplement with exogenous estrogen.

No matter how long you have been breeding horses, it can be difficult. Mare care: Breeding Tips will help you learn everything about getting your mare into foal. This free report will show you how to prepare your mare and when to breed. It also includes tips on how to order semen and induce ovulation. Get your copy now.

Regumate can also be used to maintain pregnancy in horses who appear to be returning to heat, even though an embryo is clearly visible during an ultrasound examination 14-16 days after ovulation. Regumate is also used to treat problem pregnancies and embryo transfer recipient mares. Colic, pregnant mares that have been subject to long transportation and manual reduction of a double pregnancy.

The progestin Regumate is a good choice for mares’ reproductive management. Exogenous progestins should not be used in all cases. Many mares are given the drug without any medical indication. For more information about safe and effective use, please consult your horse veterinarian. Dr. Patrick M. McCue, a reproductive specialist at Colorado State University’s Equine Reproduction Laboratory, is available to help you.

Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!