Printed in Atlantic Horse and Pony, February, 1996

When Should You Breed Your Mare?

Winter, spring, summer, fall: consider the options

By Jos Mottershead

Once you have selected a suitable stallion for your mare, and completed all the paperwork required for arranging a contract, you must decide when you want the foal to arrive. Equine pregnancies last about 11 months, so your decision on the date of delivery will determine when you breed your mare.

Mares are seasonally polyestrous - they have multiple estrus (heat) cycles during one part of the year and none at another. These two periods are separated by transitional phases, during which mares experience irregular estrous cycles, either longer or shorter than normal. In the northern hemisphere, mares show a lack of estrus from roughly November through to March. If they do show signs of heat, they will probably not ovulate, and if they are bred they will not conceive. This is nature's way of preventing the arrival of a foal in the middle of the winter, when temperatures are low, and food scarce.

A major consideration in deciding how early in the year to breed your is your intended use for the foal. Horses have an "official birthday" on January 1st, although most experts agree that it would make more sense for horses in the northern hemisphere to have it on April or May 1st.


If you intend to race the foal, or shown in futurities, you will probably want your mare to foal early, in January or February, to allow for maximum growth during the year. To accomplish this goal, you would have to breed the mare in February or March.

To breed this early, you must manipulate the mare's natural cycling tendencies, using artificial light, to persuade her that spring has arrived early. You must start this process 60 to 80 days prior to the desired onset of regular cycling. Doing so will allow the mare to complete at least one, preferably, two regular cycles each consisting of five to seven days of standing heat, followed by 14-16 days out of heat, prior to breeding. The artificial lighting must be started in November in order to breed in February.

If you have not started this by the time you read this (February), you can pretty much give up the idea of a very early foal next year! If you are planning to have an early foal another year, you should consider whether your stabling is sufficient. Obviously, you will have to provide adequate shelter for the mare and foal in 11 months time, but using artificial lighting to stimulate early cycling will cause the mare to shed her winter coat early, so don't plan to build the foaling location during the summer. The mare will need extra warmth before she's even bred.

There are other things to think about if you are planning a winter foal, especially if you are inexperienced at foaling. A veterinarian may not be able to reach you during stormy weather if you live "off the beaten track".If necessary transporting your mare or mare and foal to a veterinary facility, such as the Atlantic Veterinary College in Charlottetown could also be difficult over winter roads. At a more basic level, you may not want to be get up every hour through the night to check your mare when it's -14 C. or colder.


If you are not under pressure to have an early foal, then the late May to mid July period is probably the best. The foal will be born in mild weather, and grow substantially before winter rolls around again. By the end of their third year, foals born at this time will have caught up developmentally with those foaled earlier.

During this period, the mare and foal will also be at pasture at a time when there is good nutrient value in the grass. If you have an early or late foal, you will have to supplement the feed for both the mare and foal to a greater extent.

Mares can also foal outside during these warmer months. Many authorities recommended the outdoors as the best place to foal, but you must provide shelter from direct sunlight, and avoid the time when flies are at their worst in your area.


Breeding later than August gives rise to a host of other considerations. The mare may be in transitional cycle phase by this time, with erratic heats. If your mare does not become pregnant on the first heat cycle she is bred on she will have an even later foal.

If you breed for a late foal, your mare will be carrying the foal through the warm summer months. She will be uncomfortable, and you will not be able to ride or drive her.

Weaning is always a difficult procedure, and it may be even more difficult for a late foal, especially if you do not have a lot of stall space, and the mare and foal are able to see each other. Earlier in the year, the mare can be put in the barn, and the foal kept with other foals at pasture.


Regardless of what breeding time you decide on, talk to the stallion owner. An early booking or breeding discount may be connected with the stud fee. If there is an early booking discount, find out whether the mare have to be bred by a certain date. Ask if the stallion is available for breeding year round. Many stallions compete, and are therefore not available at certain times. If you are using transported cooled semen, you must ensure that the stallion owners will ship semen at all times, or if not, when they will.

© 1996 Jos Mottershead, Atlantic Horse and Pony Magazine and
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