Question
I have been struggling to keep weight on my Arabian mare (12 years old, 780 lb or 354 kg) due to her extensive training schedule for endurance competitions, so I contacted my vet for advice. He suggested I feed soybean or canola oil. However, I have heard some discouraging reports about the digestibility of oil. For example, because horses do not have a gall bladder, I have heard it is very hard for horses to digest the oil, which in turn decreases the availability of other essential vitamins and minerals. Is there any legitimacy to this statement? Is it OK to give oil to horses?
Answer
Most studies have found that fat is 90% digestible in the horse. Even though the horse does not have a gall bladder, the liver produces bile, which is released into the small intestine and emulsifies the fats in the digestive tract to prepare them for digestion. From there, fat digestion in the horse is the same as in the human; from the digestive tract, fat travels by way of the lymph system to the liver and then it is distributed throughout the body.
Certain vitamins (A, D, and E) require fat in the diet to facilitate their absorption. Called fat-soluble vitamins, they are handled by the body in the same way as fats (absorbed into the lymph system and spread from the liver). Fats help carry vitamins to and through the liver.
Kentucky Equine Research (KER) has done extensive studies on fat supplementation. Researchers investigated the effect of a high-fat diet on the digestibility of other nutrients and found no significant decrease in the digestion of any minerals or other nutrients, such as protein or fiber.
Of course, there is a limit to the amount of fat the horse can digest, with the maximum about 15% of the total diet, forage included, and there is a bit of difference depending on whether it is vegetable or animal fat (vegetable is better digested). Normal feeding rates of oil are usually between one-fourth cup and two cups per day, and are generally tolerated well. There is also a limit on the amount each horse will tolerate in its feed without losing interest in eating it, but that seems to vary from horse to horse. You know if you are feeding too much fat if a horse refuses the feed or if changes in manure occur (loose and glossy; more like cowpies than road apples).
Fat provides three times the calories of an equal weight of oats, so it is a concentrated source of energy. It increases the caloric density of the diet without increasing the bulk.
High-fat diets have been used in endurance horses for years with success. There is another advantage to feeding fat: with regular feeding it will improve the utilization of fat as a fuel source for exercise, thereby sparing muscle glycogen. It does take an adaptation period to rev up this mechanism, so it would be best to start feeding fat at least three to four weeks before the next major competition.
Oil is a good way to supplement fat, and either canola or soybean is suitable. Although horses find corn oil most palatable, it is not recommended anymore because it is high in omega-6 fatty acids and practically void of omega-3 fatty acids. Equine nutritionists believe that it is important to keep a balance of omega-3 to omega-6 fatty acids in the diet. Oils like canola have more omega-3s than corn oil.
If you’d rather not feed oil, there are other high-fat feedstuffs, such as rice bran, linseed, and chia. Linseed and chia are especially high in omega-3s.
