Fillies

A filly is a young female horse. In common usage, the term refers to a female horse that is under four years old, though in some contexts four years or older is considered a mare. Fillies are distinguished from mares, which are adult female horses.

Young horses are categorized by age: a foal is a horse from birth to weaning; a weanling is a recently weaned foal; a yearling is one year old. A filly becomes a mare as she reaches reproductive maturity, typically around four years of age, but definitions vary by breed and discipline.

In sport and breeding, fillies may perform as athletes in races specifically for fillies, such as the Oaks or Kentucky Oaks, and they can also join open races with colts and geldings under certain rules. In breeding, fillies are kept for future breeding as mares; many are kept for potential broodmares, while some are sold or retrained for other disciplines.

Care for fillies includes appropriate nutrition to support growth, routine veterinary care, vaccinations, parasite control, dental care, hoof care, and exercise under guidance. Early handling and training emphasize welfare, safety, and gradual conditioning. Proper social housing and boarding are important for development.