Mare Care

Breeding — The Goal of Getting in Foal

There’s nothing more gratifying for a breeder than a promising new foal hitting the ground, but a successful outcome starts months prior. The initial breeding and identifying the time of ovulation are crucial for a successful outcome. Most breedings will result in conception when they occur 24 to 36 hours before ovulation or the day of ovulation.

During winter and early spring before your mare is bred, open mares experience winter anestrus followed by a transitional period preceding the onset of regular estrous cycles.


  • Mares have a 21-day estrous cycle.
  • Behavioral estrus (heat) lasts five to seven days.
  • Ovulation occurs one to two days before the end of estrus.

There are several tools you can use to approximate ovulation and help facilitate scheduled breeding, including:

Your best resource for breeding management is your veterinarian. He or she can accurately predict ovulation and help you more efficiently manage your breeding program.

Put your mare’s cycle on your schedule.
As the synthetic form of progesterone, progestins have several applications in a breeding program:

  • Suppress estrus in mares.
  • Facilitate attainment of regular cycles in the transitional mare.
  • Facilitate management of the mare exhibiting prolonged estrus.
  • Facilitate scheduled breeding.

Oral progestin hormone, Regu-Mate® (altrenogest), effectively suppresses estrus during the time it’s administered. When treatment is discontinued, mares come in estrus within 4 to 5 days and ovulate within 5 to 7 days following the onset of estrus. Mares with active ovaries (follicles greater than 20 mm in diameter) frequently respond with regular post-treatment estrus cycles. Progestin treatment can be started at any point in a mare’s cycle.

The use of Regu-Mate® (altrenogest) to suppress estrus in order to facilitate scheduled breeding requires a veterinarian’s prescription and consultation. Ask your veterinarian to put together a breeding plan customized for your operation.

Talk to your veterinarian about proper use and safe handling of Regu-Mate®. Avoid skin contact. Always wear protective gloves when administering Regu-Mate®. This product is contraindicated for use in mares with a previous or current history of uterine inflammation. Pregnant women, or women who suspect they are pregnant, should not handle this product. For complete safety information, please read label.