Aging Horses by their…Telomeres?

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.

In this study, the researchers compared the length of telomeres in the PBMCs of 19 mixed-breed horses from 1 to 25 years of age. They attempted to correlate changes in telomere length with age-related alterations in various immune responses.

Younger horses with longer telomeres had higher antibody concentrations and higher rates of cellular replication as well as lower concentrations of inflammatory mediators.  The older horses had shorter telomeres, reduced antibody concentrations, decreased cellular immune responses, as well as increased production of pro-inflammatory cytokines.

"One surprising finding from our work was that not all of the horses showed the same degree of telomere erosion or immune dysfunction," Horohov said.  "Some of the oldest horses had relatively long telomeres while some younger ones had shorter telomeres."

Further research to assess the overall impact of age and telomere length on equine health is required.  In particular, the impact of environment, prior exposure to disease-causing organisms, and genetics on telomere length remain to be investigated.  Understanding these processes could lead to better approaches to assure improved health in the aged horse.

The study, "The effect of age and telomere length on immune function in the horse," was published in the July 2008 edition of Developmental & Comparative Immunology

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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