Instructions
How to Tell If a Mare Is in Heat
Watch for behavioral changes. Some mares will show personality changes while in heat, such as grumpiness, irritability, and anxiety. That behavior may be directed toward other horses, toward humans, or both.
If possible, introduce the mare to a stallion to see how she behaves. If your mare is in heat, she will be accepting of the stallion and may overtly encourage the stallion to mount her. If your mare is not in heat, she will likely kick, bite, or show other hostile behavior toward the stallion.
Look for signs of "winking" if you suspect your mare is in heat. Winking is a term used to describe the opening and closing of the lower vulva by a mare during her heat cycle. While this phenomenon is difficult to describe in words, it is very obvious upon visual inspection.
Determine if your mare is urinating more frequently than normal by keeping track of her habits. Mares in heat will often urinate small amounts often, and some may squat and spread their legs when urinating. If her urine is dark or blood-tinged, she should be seen by a veterinarian to rule out an infection or other problem.
Take your mare for an ultrasound and examination. An evaluation will determine if your mare is in heat, while helping to pinpoint exactly where she is in her cycle. This is really only necessary if you suspect infertility based on multiple failed breeding attempts.
How to Tell If a Mare Is in Heat
A mare's estrous cycles usually only occur in the spring, summer, and early fall. Mares cycle approximately once every 21-23 days, with some mares having longer or shorter cycles. Knowing how to tell if a mare is in heat is important if you want to breed her or need to predict mood changes that may interfere with training or other activities.