Published February, 2015

Sure, age is just a number, but human doctors know that's not necessarily the case when it comes to nutrition and nutrient digestibility. So do aged horses follow this same pattern? Does aging correlate with a reduced ability to digest vital nutrients even in healthy horses? That’s what an international research team recently sought to find out.

Sarah Elzinga, MS, now a PhD candidate at the University of Kentucky Gluck Equine Research Center, in Lexington, worked with colleagues from the Michigan State University Department of Animal Science, in East Lansing, and the WALTHAM Center for Pet Nutrition, in Leicestershire, U.K., to compare nutrient digestibility in mature and senior horses. The team employed 17 healthy stock-type mares—nine adults (5-12 years old) and eight aged (19-28 years old). The team matched each adult and aged mare by body condition and randomly assigned each pair to consume a diet consisting of either:

• Mixed timothy hay (HAY);
• Mixed timothy hay with a high-fiber, high-fat, low-starch concentrate (FF); or
• Mixed timothy hay with a low-fat, high-starch concentrate (CHO).

The mares consumed each diet for six weeks before being reassigned so that each mare ultimately ate all three diets. The team evaluated how well the mares digested a variety of parameters including digestible energy, dry matter, calcium, phosphorus, energy, neutral detergent fiber (an estimate of how much "bulk" forage [cellulose, hemicelluloses, and lignin] a horse can consume), crude protein, and fat.

Ultimately, the team identified no differences between healthy adult and aged mares with regard to any of the parameters measured. These results indicate that, while older horses might have health concerns that warrant specialized diets, there's no need to change a healthy senior horse's diet just because he reaches a certain age.

Although all the aged mares in this study had normal dentition, the authors cautioned that poor or missing teeth could negatively impact nutrient digestion.

“The aged horse population is growing, with horse owners increasingly concerned with how to care for these animals," said Elzinga. "Our research shows that the healthy aged horse is able to digest various nutrients similarly to a horse in its prime."

The study, "Comparison of Nutrient Digestibility Between Adult and Aged Horses," was published in the Journal of Equine Veterinary Science. 

Kristen M. Janicki, MS, PAS provided this information.