Breeding Mares & Heat Cycles

Best times to breed your mare.

The mare's heat cycle is referred to as equine estrus, estrous or oestrous cycle. It is the period of time which she will produce a fertile egg (or ovulate) and will accept a stallion. A mares best times for coming into heat are the warmer and longer days of the year, such as mid to late spring and the summer months.

Most mares will come into heat every 21 days. Usually 21 days after the day the mare first comes into heat, she will start into heat again, but some mares vary anywhere from 18 to 31 days in their heat cycles. Heat periods are generally longer earlier in the breeding season and many older mares have longer than average heat cycles.

Ovulation, or the period of time when the mare is fertile and can conceive a foal generally only occurs 24 to 48 hours before the mare goes out of heat. Thus no matter how long she is in heat, ovulation will only occur shortly before the end of her heat cycle. Sperm will only live in the mare's reproduction tract for about 24 hours, so it is absolutely necessary to breed her shortly before she goes out of heat. It is best to breed the mare on the second day of her heat cycle and then breed her every other day until she goes out of heat. That way she will have live sperm in her genital tract when the egg is released from the ovary.

Mare's that have just foaled will come into heat about 9 days after the foal is born, but sometimes this varies from 4 to 18 days. This is called the "foal heat". You can breed her at this time if she foaled cleanly and without complications. If she had problems foaling, then you should at least wait until her next heat period which will usually occur 18 to 21 days after the foal heat. This will give her time to heal and get ready to rebreed.

A mare is not too old to breed if she is in good health and if bred to a stallion expected to produce a foal of normal size. Foaling or birthing is easier on younger mares because their pelvis is held together with more cartilage than bone. You should keep a closer eye on an older bred mare.


Please note: All mares used for breeding should be examined and under a veterinarians supervision. The above tips are not meant as a diagnosis, treatment advise or replacement for the medical advisement of your veterinarian. It is offered as a general informational resource based on personal experience and study.

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