At what age does a horse become “aged” or “senior” with respect to nutrition? At 10? 15? 20?

NRC 2007 suggests 3 ways in which “old age” can be defined:

  1. chronologic – number of years from birth
  2. physiologic – the decline in physiologic functions as the threshold for old age
  3. demographic – reflects an age-group population within the whole horse population.

Many nutritional studies done on older horses have arbitrarily used 20 years of age as the threshold for “aged” or “senior”. NRC 2007 suggests the best way to define this population of horses may be a combination of chronological age and physiological signs of aging.

Some physical signs of aging are:

  1. Loss of body score (body condition or body fat)
  2. Graying of the haircoat, especially on the muzzle and around the eyes
  3. Loss of muscle along the topline – may lead to a “swaybacked” appearance
  4. Hollowing out above the eyes
  5. Dental disease and/or loss of teeth

Loss of body condition and muscle along the topline could be related to less efficient processing of certain nutrients in the older horse, most notably protein. Tribute Equine Nutrition, as well as others, has found improving the amino acid balance in the older horse may help reverse such changes.

Other research has shown potential diminished ability to digest fiber and absorb phosphorous with age. There is conflicting evidence on age-related differences in Vitamin C status between young and older horses, but adding an antioxidant like Vitamin C to older-horse diets will not be deleterious and may help with body cell health.

Older horses are also prone to Cushing’s Disease (or Syndrome), which is discussed in a separate article. Hyperglycemia (elevated blood glucose) and hyperinsulinemia (elevated blood insulin) can be associated with Cushing’s Disease, but can also occur in other metabolic conditions such as Insulin Resistance (IR) or Equine Metabolic Syndrome (EMS), also discussed more fully in other articles.

In addition, Cushing’s horses often lose muscle mass to a higher degree than a normal aging horse. Again, improving the amino acid balance (not just feeding MORE protein) can help reverse the loss of or maintain muscle mass.

Providing calories in the form of highly digestible fiber from sources like beet pulp, soy hulls and dehydrated alfalfa meal, as well as from fat, can lessen the dietary effects on blood glucose and insulin in affected horses. Dental issues also likely to contribute to poorer digestion in the older horse, especially fiber digestibility.
Though a number of nutritional studies have been done on older horses, there is not enough evidence to support age-related changes in nutrient requirements, according to the NRC 2007 Committee on Horse Nutrition.

Regardless, some evidence suggests there may be some effects of aging on nutrient metabolism, and formulating diets for older horses using this information is certainly not harmful, and may help.

Suggestions for TOTAL diet – hay and grain combined (dry matter basis):

  1. 12-14% protein. Make sure protein QUALITY is high.
  2. 03. – 0.4% phosphorous.
  3. 0.6 – 0.8% calcium.
  4. increase Vitamin C?

Management suggestions:

If the horse can still eat hay:

  1. Use higher fat, and/or heat-processed feed (like extruded or pelleted)
  2. Extrusion/heat-processing increases foregut digestibility
  3. Assure adequate intake of all other vitamins and minerals
  4. Offer free-choice vitamin/mineral mix designed for horses eating grass hay

Tribute Suggestions:

If the horse cannot eat hay (leaves wads of hay by feeder – “quidding”)

  1. Feed complete feed with highly digestible fiber
    • beet pulp
    • dehydrated alfalfa meal
    • soy hulls
  2. Assure high quality sources of protein, vitamins and minerals
    • soybean meal
    • appropriate chelated minerals
  3. If horse can’t chew well, can make slurry of complete (and/or) extruded feed
  4. Feed at least 4x a day
  5. Total intake should be 1.5 – 2.0% of horse’s body weight (15 – 20 lbs. For 1,000 lb. Horse)

Tribute Suggestions:

D.J. Burke, Ph.D.