A filly is defined as a female horse less than how many years of age?

A filly is defined as a female horse that is less than three years of age. This definition is important as it separates younger female horses from mares, which typically refers to adult female horses generally over the age of three. Understanding this age classification helps in proper horse management, training, and breeding practices, as different life stages may require varying care and handling techniques. A filly is still developing, and recognizing her age influences everything from nutrition to training goals, ensuring her well-being as she matures into a mare.