<P> A colt is a male horse, usually below the age of four years . </P> <P> The term "colt" only describes young male horses and is not to be confused with foal, which is a horse of either sex less than one year of age . Similarly, a yearling is a horse of either sex between the ages of one and two . A young female horse is called a filly, and a mare once she is an adult animal . In horse racing, particularly for Thoroughbreds in the United Kingdom, a colt is defined as an uncastrated male from the age of two up to and including the age of four . </P> <P> An adult male horse if left intact is called either a "stallion" or a "horse" (sometimes full horse); if castrated, it is called a gelding . In some cases, particularly informal nomenclature, a gelding under four years is still called a colt . A rig or ridgling is a male equine with a retained testicle or one which has been incompletely castrated . </P>

At what age is a colt considered a stallion