Q. What role does fat play in feeding horses, and what’s the recommended percentage of fat for the equine diet?

—Barbara, North Carolina

A. Typically, when we think of feeding fat to horses, it is to increase the energy density in the diet. Fat is a good candidate for this because it provides 2.25 times more calories per gram than the same amount of carbohydrate. Research suggests increasing calories from fat rather than simple carbohydrates might help your horse stay levelheaded compared to feeding the same additional calories from starch.

Feeding some fat in the ration offers other benefits, as well. Over time, as horses adjust to having fat in the diet as an energy source, metabolic adaptations can occur that increase fat oxidation during exercise. Because the body can only use fat as a fuel when working aerobically, this switch to preferentially burning fat as a fuel when working aerobically preserves glycogen stores for use during anaerobic work. This can potentially increase time to fatigue. Another important role of dietary fat is facilitating the absorption of fat-soluble vitamins such as A, D, E, and K.

Certain types of fat provide sources of essential long-chain fatty acids. These include the polyunsaturated fatty acids (PUFAs) linoleic acid and alpha-linolenic acid. These and other PUFAs play structural roles within cells and are precursors for important hormonelike compounds such as prostaglandins and eicosanoids. They’re also involved in inflammatory response.

A forage-based diet comprising predominantly good-quality pasture might offer 2-5% fat. This will be lower (about 2-3%) in conserved forage diets because the process of curing hay can damage fat composition. Diets of good-quality pasture will have higher levels of omega-3 than omega-6 fatty acids—about three times more. Conversely, hay-based diets have closer to two times more omega-3 than omega-6 fatty acids. Once you add concentrate feed, the amount of omega-6 fat tends to be higher than omega-3. This potentially has implications at the cellular level, because omega-3 and -6 fats have different impacts on inflammatory response. As a result, feeding horses supplemental sources of omega-3 fatty acids has become popular.

Omega-6 fats have developed a bad reputation in recent years, as they are labeled as being proinflammatory, while the omega-3 fats are deemed anti-inflammatory. However, in certain situations some level of inflammation is beneficial. In fact, the National Research Council (NRC) doesn’t give an equine requirement for omega-3 fat but does for the omega-6 fatty acid linoleic acid. This doesn’t mean omega-3 fats are not required, but a requirement has not been quantified.

Horses’ linolenic acid requirement is about 50 grams per day for a 500-kilogram (1,100-pound) horse eating 2% of its body weight in forage per day. A 500-kilogram horse eating 10 kilograms of dry matter from fresh pasture with a fat content of 3% fat is consuming 300 grams of fat per day. Most commercial feeds with a 4% fat content or more include a fat source such as rice bran or some kind of plant-based oil. The higher the fat percentage, the more of these ingredients the feed contains.

With consumer demand for higher omega-3 levels, more feed companies are including ingredients such as flax, which provides both omega-3 and -6 PUFAs. If you’re feeding your horse 6 pounds of a 12% fat performance feed, you’re feeding 490 grams of fat and, therefore, easily exceeding the NRC’s minimum recommendations. On the far end of what amount of fat horses can handle in their diets, research has shown they can digest and utilize up to 20% of their diet by weight as oil.

Take-Home Message

Whether feeding a small amount to help improve coat quality or a larger amount to help maintain condition, fat is an important nutrient in the equine diet. If you want to increase calories from fat in your horse’s ration for weight gain, a fortified high-fat feed, as opposed to oil, has the benefit of being fortified with other nutrients to help ensure a properly balanced diet.