Thinking of changing your veteran’s diet?

Does nutrient digestibility decline with age? Researchers at Michigan State University investigated.

In species such as humans, rats, and dogs, altered nutritional requirements associated with aging include a decrease in energy requirement. Older cats also experience a decrease in their ability to digest fat and protein, and older dogs have an increased requirement for protein.  There is little research comparing digestibility in healthy adult versus healthy aged horses.

Researchers from Michigan State University investigated whether there was a difference in macronutrient digestibility between 8 adult (5 to 12 years) and 9 aged (19 to 28 years) horses fed 3 different diets.

The horses (all mares) were pre-examined to ensure normal dentition then randomly assigned one of three diets for a 5-week period:

  1. hay only
  2. hay plus a starch and sugar-rich concentrate
  3. hay plus a fat (oil) and fiber-rich concentrate

Each diet period was comprised of 3 weeks of outdoor group dry lot feeding, 2 weeks of indoor stalled individual feeding, followed by a 72-hour digestibility trial including total urine and fecal collection.

Feed, fecal, and/or urine samples were analyzed to calculate dry matter (DM), crude protein (CP), fat, energy, calcium (Ca), and phosphorus (P) apparent retention as well as apparent digestibility. Neutral detergent fiber (NDF) digestibility was also determined.

Researchers found the following:

Body condition score (BCS), did not differ between age groups but average bodyweight was lower in aged than adult horses.

No age differences in digestibility, apparent digestibility, or apparent retention were seen for any of the variables measured.

Researchers were able to conclude that total tract macronutrient digestibility appeared to be similar between healthy adult and aged horses.

Although the horses in the present study did not appear to have any problems, decreasing appetite is one of the biggest issues associated with age and nutrition in humans, dogs, cats, and horses. This can contribute enormously to inadequate intake of nutrients and often leads to subsequent health problems. In addition, older horses often have poor dentition, which can make mastication difficult or painful. This initially limits the breakdown of feedstuffs and, if severe enough, can lead to decreased intake.

This study indicates that, providing they are in good health and body condition, older horses (aged 19+) do not automatically require changes to their core diet.


Elzinga, S., Nielsen, B.D., Schott, H.C., Rapson, J., Robison, C.I., McCutcheon, J., Harris, P.A. and Geor, R., 2014. Comparison of Nutrient Digestibility Between Adult and Aged Horses. Journal of Equine Veterinary Science34(10), pp.1164-1169.