To guess a horse’s age you can look at his teeth … or the length of his telomeres and his immune system function, according to researchers with the University of Kentucky’s Gluck Equine Research Center.

Scientists studying the mechanisms behind aging-related decline in immune function of horses confirmed that telomere erosion–progressive shortening of the specialized protective “caps” found at the end of chromosomes—occurs as horses age. 

Telomeres are thought to function as a type of cellular “clock.” Once the telomeres become too short, the cell is incapable of replicating and dies. Telomere shortening occurs as all species age, although its significance remains unclear.

“It was hypothesized that a reduction in telomere length in peripheral blood mononuclear cells (PBMCs, a particular type of white blood cell in the bloodstream) plays an important role in age-related changes and deterioration of immune responses,” said David W. Horohov, MS, PhD, professor of immunology and the William Robert Mills Chair in Equine Infectious Diseases at the Gluck Center