Despite the fact they don’t have gallbladders, horses digest fat well if it is introduced slowly into the diet. But why would a species that evolved on forage need fat?
As it turns out, horses benefit from fat in several ways. According to Catherine Whitehouse, M.S., a nutrition advisor at Kentucky Equine Research, “Dietary fat is necessary for the absorption of the fat-soluble vitamins, A, D, E, and K, but it has turned into a useful feedstuff outside of that.”
In addition to its role in vitamin absorption, fat contains nine calories per gram, as opposed to carbohydrates, which contain four calories per gram, making fat more than two times as energy dense. “For a hard keeper, a horse owner can add significant calories by supplementing fat. Further, research described in the National Research Council’s Nutrient Requirements of Horses suggests that horses adapted to higher fat diets may have improved endurance by sparing glucose and burning fat for energy,” said Whitehouse.
Fat is also an alternative energy source for horses that require limited carbohydrates, such as horses suffering from certain muscle diseases (polysaccharide storage myopathy, recurrent exertional rhabdomyolysis) and those prone to laminitis.
Fat can be incorporated into a horse’s diet in numerous ways. One of the most common methods is top-dressing a concentrate with oil. Benefits of vegetable oil include low expense, availability, and ease of feeding. Disadvantages include messiness, unpalatability in some horses, and inconsistent products.
Fat also supplies omega-3 and omega-6 essential fatty acids. According to Nutrient Requirements of Horses, soy, corn, sunflower, and safflower oils are rich in omega-6 fatty acids, whereas flaxseed oil is rich in omega-3 fatty acids. Deodorized fish oil, such as EOâ€¢3, offers a direct source of long-chain omega-3 fatty acids. Of particular importance to health and well-being are the omega-3 fatty acids known as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).
Other fat sources include stabilized rice bran and flaxseed, both of which are palatable to horses. Some commercial feed companies produce fat supplements that may be extruded or pelleted. Fat alone is devoid of balanced nutrients, so some commercially produced products include vitamin and mineral fortification as an added benefit.
When top-dressed, oil is absorbed well by most commercial feeds, beet pulp, and hay cubes. When the feed absorbs oil, it tends to make it harder for the horse to sort out and pools less at the bottom of the feed bucket. If a horse leaves oil behind, it is important to clean out the feed bucket so the fat does not become rancid. Spoiled fat can pose a health risk if the horse consumes it.
As with any change, adding fat to a horse’s diet should be done slowly, and maximum benefits may take several weeks to manifest. If the feeding goal is to feed 1 cup (237 ml) of oil per day, begin with offering one-fourth cup (60 ml) for four or five days, and then increase to one-half cup (120 ml). Continue increasing the amount oil fed daily slowly until the full cup can be given.
If a horse presents with greasy or loose manure or refuses to eat the feed after the addition of fat, reduce the amount offered for several days, then gradually start to add fat back over the course of two to three weeks. Most horses tolerate fat well if properly adapted.