Q.Is it true that senior horse feed isn’t really suitable for older horses because they have a high fiber content, and aged horses don’t actually digest the nutrients, they just run through their digestive tracts?

—Via e-mail

A.Many senior feeds are high in crude fiber compared to other types of commercial feeds because they are complete feeds. This mean they contain all the forage a horse needs in the diet. You can give complete feed as a horse’s sole diet with no additional hay or pasture. To maintain hindgut function when fed alone, fiber content in these feeds must be high. Typically, the percent crude fiber in senior feeds is in the high teens or low 20s.

This amount of fiber is high compared to what you’ll see on feed tags for products formulated for performance and growing horses, but the crude fiber content of senior feeds is well below what hay contains. A hay pellet might easily contain 30% crude fiber. The crude fiber amount is supposed measure the indigestible portion of carbohydrates within a feed, yet it’s likely an underestimate of what’s truly indigestible.

While these feeds’ crude fiber portions might not be particularly digestible, it’s incorrect to say that because of this the horse can’t digest other nutrients. Fiber is only one component in a feed, and it’s not the sole source of nutrients. Most commercial senior feeds utilize readily digestible feed ingredients such as beet pulp, rice bran, wheat middlings, soybean meal, vegetable oil, and possibly grains such as oats. These feed ingredients provide sources of quality protein, fat, and readily available carbohydrates. Additionally, senior feeds are fortified with essential vitamins and minerals. Often these vitamins and minerals are included at rates higher than in feeds for other mature horses, because senior horses might have a decreased ability to absorb some minerals.

Also, senior feeds’ physical form makes them more digestible than, for example, hay. The particle size of commercial feeds is small, and this increases the relative surface area that digestive enzymes and intestinal bacteria have to work compared to the particle sizes of chewed hay. As a result, the nutrients in senior horse feed are likely better utilized.

A well-formulated complete senior horse feed with adequate crude fiber can be wonderful substitution in the diet for equids with no access to pasture or unable to consume long-stem hay.