No difference was found in healthy horses.
The population of horses 20 years of age and older is rising, and little research exists exploring the differences in nutrient digestibility in aged horses versus adult horses. It is widely accepted that aged horses have a decreased ability to absorb nutrients from the diet. The objective of the experiment, conducted at Michigan State University, was to compare the digestibility of various feedstuffs in healthy adult horses in contrast to healthy, aged horses.
Eight adult (5 to 12 years) and 9 aged (19 to 28 years) stock-type mares were fed. Horses were rotated through three diets: hay only, hay plus a cereal-based feed, or hay plus a fat and fiber-rich feed. Horses were housed and fed one of the three diets outdoors in a group for 3 weeks, and then indoors in individual stalls for 3 weeks to record feed refusals. During week 6 of each period, a 72 hour digestibility trial was conducted in which feed intake and feces and urine were collected. The same protocol was followed for each diet.
No age by diet interaction, or differences in daily feed and hay intake were detected. No differences in fecal or urine output were noted between the horse groups. There was no effect of age on fiber, crude protein, energy and digestibility, or mineral retention.
These results indicate that under most practical feeding scenarios, it is unlikely that differences in digestive capacity are present between adult and aged horses. However, all horses utilized in this trial were healthy, and it's possible that there are differences in compromised (i.e., diseased) older horses, or those with dental disorders.