A mare is an adult female horse or other equine. In most cases, a mare is a female horse over the age of three, and a filly is a female horse three and younger. In Thoroughbred horse racing, a mare is defined as a female horse more than four years old. The word can also be used for other female equine animals, particularly mules and zebras, but a female donkey is usually called a "jenny". A broodmare is a mare used for breeding. Reproductive cycle. Mares carry their young (called foals) for approximately 11 months from conception to birth. (Average range 320–370 days.
https://en.wikipedia.org/wiki/Mare