When does a horse first come in heat?

A horse typically comes into heat, or estrus, for the first time around 12 to 15 months of age, although this can vary based on the breed and individual development. Seasonal factors also play a role, as many mares are influenced by daylight length and may only come into heat during the spring and summer months. It's important to monitor their behavior for signs of heat, which can include increased restlessness and interest in stallions.