MSD Manual

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Pet Owner Version

Breeding and Reproduction of Horses


John A. Bukowski

, DVM, MPH, PhD;

Susan Aiello


Reviewed/Revised Jul 2011 | Modified Oct 2022
Topic Resources

Mares reach puberty at about 18 months of age and undergo an estrous, or heat, cycle. Mares go into heat repeatedly during the breeding season, which usually continues while day length is long and ends when winter approaches. Exposing mares to increasing periods of artificial light can get the breeding season started earlier. During the breeding season, mares ovulate regularly every 3 weeks, but they are in heat and receptive to a stallion for only 2 to 8 days. Heat is generally longer early in the season (spring) and only 2 to 3 days in late June. Gestation (pregnancy) lasts 330 to 342 days, with lighter breeds generally having a longer pregnancy (340 to 342 days) than heavier breeds (330 to 340 days). Pregnant mares generally have a single foal; twins are rare. Foals can see and stand to suckle soon after birth.

Nursing, horse

Nursing, horse

Foal Care

As soon as a foal is born, you should remove any mucus or other material around its nostrils to assist the foal in breathing, and coat the umbilical stump with iodine to prevent bacteria from entering the body and causing a serious blood infection. The foal should begin to nurse within the first 1 to 2 hours. This is critical because the initial mare’s milk, called colostrum, contains antibodies that provide the young foal with immunity against disease. If the mare rejects the foal, a milk replacer can be used as a substitute. Foals should also have a bowel movement within their first 2 hours or so; if they do not, you will need to give the foal an enema. Contact your veterinarian immediately if the foal does not begin to nurse, or if you observe any other problems during the first few hours after foaling.

As much as possible, the mare and the foal should not be disturbed. Many mares are very protective of their foals, and someone will likely have to hold the mare while another person attends to the foal’s needs, such as removing mucus, coating the umbilical stump, and so forth.

You should spend at least 15 minutes every day with a new foal, touching its hooves, ears, nose, and other body parts, as well as tapping on its feet and generally rubbing it all over. Handling a foal early on will make it much easier to handle as an adult.

Vaccinations usually begin around the age of 3 months, with appropriate booster vaccinations 1 month later. Vaccination for equine influenza generally begins when the foal is 8 to 10 months old. Your veterinarian can advise you on the best vaccination program for your foal.

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