Template:Short description Template:About A filly is a female horse that is too young to be called a mare. There are two specific definitions in use:
- In most cases, a filly is a female horse under four years old.
- In some nations, such as the United Kingdom and the United States, the world of horse racing sets the cutoff age for fillies as five.<ref>Template:Cite book</ref><ref>Template:Cite news (Zenyatta was foaled in 2004, making her a 4-year-old at the time.)</ref>
Fillies are sexually mature by two and are sometimes bred at that age, but generally, they should not be bred until they themselves have stopped growing, usually by four or five.<ref name=HandH149>Ensminger, M. E. Horses and Horsemanship: Animal Agriculture Series. Sixth Edition. Interstate Publishers, 1990. Template:ISBN p. 149-150</ref> Some fillies may exhibit estrus as yearlings.
The equivalent term for a male is a colt. When horses of either sex are less than one year, they are referred to as foals.<ref>Template:Cite book</ref> Horses of either sex between one and two years old may be called yearlings.