When a mare gives birth to a colt, she is referred to as the colt's mother. The term colt refers to a young male horse, and mare is the term used for a female horse. A colt mother is therefore simply a mare who has given birth to a colt.
Mares typically give birth to one foal at a time, although twins and triplets are not unheard of. The average gestation period for a mare is 11 months. After giving birth, the mare will produce milk for her foal which is high in fat and nutrients essential for the foal's growth and development.