Once the stallion is mounted, he will insert his penis into the mare's vagina and ejaculate. The mare's cervix will then close, preventing the sperm from leaking out. The sperm will then travel through the mare's reproductive tract and fertilise an egg. If the egg is fertilised, it will develop into an embryo and then a foetus. The mare will then carry the foal (baby horse) for about 11 months before giving birth.
Horses can only breed with other horses. They cannot breed with other animals, such as donkeys or zebras.