"Old Billy," an English draft horse, was the longest living horse when he died at age 62, according to the Guinness Book of World Records. Although most horse owners know their hoofed friends probably will not make it into the record books for longevity, geriatric horses can live a happy and fulfilling life.

Jill Eyles, DVM, is an equine surgery intern at the University of Illinois College of Veterinary Medicine in Urbana. "I would consider most horses geriatric by 20," she said.

"Old" is a relative term depending upon the use of the horse. For example, racehorses are old by age five or six, but for a hunter-jumper that is still young.

Just as with humans, there is no age at which retirement should be mandatory. "Regular exercise is the best thing for horses that are sound enough to do so," advised Eyles. Pay attention to how your horse feels when exercised