Your 20-year-old gelding is starting to look like a senior citizen; there’s more sway in his back and less bounce to his step. Horses generally don’t become senile or as physically frail as elderly humans, but their bodies go through a number of physical changes as they grow older.

Julia Wilson, DVM, Dipl. ACVIM, of Turner Wilson Equine Consulting LLC, in Stillwater, Minn., says horses experience both external signs of aging as well as internal changes. The gastrointestinal (GI) tract, heart, immune system, and other body systems might not function as efficiently as they did when the horse was younger.

Debra Powell, MS, PhD, associate professor at The Ohio State University Agricultural Technical Institute, says most people consider old age in horses to be 18-plus.

"Some individuals age more quickly or slowly, depending on physiologic conditions," she explains. "Some show signs of aging as early as 16, and some don’t look old until they’re in their mid-20s. We see more evidence of aging problems today, just because horses are living longer, thanks to good care. Life expectancy has increased." She adds that some horses age more quickly simply due to genetics