Feeding fat (oil) to horses

Fats and oils are made up of triglycerides that each consist of a glycerol molecule to which three long chain fatty acids are attached. Fats and oils are the same compounds nutritionally; however, oil at room temperature will be a free-flowing liquid, whereas fat at room temperature will be solid. Fats/oils are digested in the small intestine of the horse and are a concentrated source of dietary energy, providing approximately 2.25 times more energy than an equal weight of digested carbohydrates. The typical horse diet consisting of pasture, hay only or hay plus concentrate has low amounts of fat (2-4%). The fat content in the diet can be increased by selecting feedstuffs in the concentrate part of the diet with a high fat content or by adding fats or oils. Feedstuffs high in fat include vegetable oils (100%), rice bran (15-18%), flax seeds (30-40%), and heat-treated soybeans (15-22%). In addition, commercially available fat-added concentrates typically contain 5–14% crude fat. Commercially, the level of fat or oil added to a concentrate is often limited by manufacturing constraints.

Fat provides various fatty acids for the horse. Essential fatty acid requirements have not been established for horses, however, most equine diets will likely meet essential fatty acid needs. Linoleic acid and α-linolenic acid are essential fatty acids that cannot be made by the horse and must be supplied by the diet. Omega-3 and omega-6 fatty acids have received the most attention due to their important biological roles in the body. These fatty acids help maintain cell membrane integrity, neural and retinal development. In addition, they have roles modulating immunity and inflammation. Omega 6 fatty acids promote inflammatory responses whilst Omega 3 fatty acids do not. Thus, it is more desirable to have greater amounts of Omega 3’s compared to Omega 6’s. There are many different oils and brands on the market and it may be difficult to decide which oil is the best to feed? Forages, flaxseed, and fish oils are typically rich sources of omega-3 fatty acids, whereas cereal grains, vegetable oils, and rice bran are high in omega-6 fatty acids. Table 1 illustrates the estimated Amounts of Omega-6 and Omega-3 fatty acids available to a 500-kg horse consuming different diets.

Fat/oil is beneficial for a number of reasons. In general, a half a scoop of oil would contain the same amount of energy as a full scoop of concentrates. For any horse that needs lower starch in the diet, oil can replace the calories lost when lowering the starch content. So, feeding supplemental fat will increase the energy density of the diet, allowing for a reduction in the amount of concentrate needed to meet the horse’s energy needs. Examples of horses requiring lower starch are horses with chronic exertional myopathies, respiratory disease (RAP/COPD), recurrent colic and gastric ulcers. The added energy can also help older horses or poor doers. Oil decreases the thermal load and enhances metabolic adaptations which potentially could improve athletic performance. Lastly, oil is great for skin and coat condition.

Supplemental oil should be introduced slowly to avoid intestinal disturbances (loose feces). Once adapted, horses can utilize up to 20% of the diet as fat. A suggested upper limit of oil supplementation is 1 ml/kg BW/day. For reference, one standard measuring cup contains 250 ml (8 fluid ounces) of oil and provides approximately 1.8 Mcal of DE. Initially, 1/4 cup of oil/day can be added to the ration. Over a two to three week period, the amount of added oil can be increased up to 2 cups per day, divided into 2 to 3 feedings.

One concern with the addition of a substantial amount of oil per day to an existing ration is an unbalanced diet. Fats/oils exposed to air and light may degrade which can lead to reduced palatability, loss of vitamins and formation of pro-inflammatory compounds. Supplementation with vitamin E (1-1.5 IU/ml added oil) may be needed to prevent oxidant stress or rancidity. Alternatively, some oil products with added vitamin E are available. Commercial concentrates with added oil are fortified to maintain appropriate nutrient-to-calorie ratios, and are designed to complement the forage source.

Fat is an ideal source of added energy as it does not provide any other nutrient. Fat/oil can be top-dressed or a high-fat commercial diet can be used. The level of fat to include will depend on the feeding goals and desired outcome. Be careful of feeding too much fat indiscriminately because a horse can become overweight. Have a goal in mind when using high-fat diets for horses.

Table 1  . Estimated Amounts of Omega-6 and Omega-3 Fatty Acids Available to a 500-kg Horse From Different Types of Diets^a,b,c

^aThe estimates above were based on the following assumptions: a) 500-kg horse with a daily intake of 10 kg DM; b) hay + concentrate diets are based on total DM intake consisting of 50% hay and 50% as concentrate; c) concentrates are made up predominantly of cereal grains, grain byproducts and oil seed meals; d) corn oil, which is rich in omega-6, was used as the fat source for the concentrates with 6 and 10% crude fat; and e) 50% of the fatty acids in forages, 75% of the fatty acids in cereal grains, and 100% of the fatty acids in corn oil are available for absorption in the small intestine.
^bOmega-6 and omega-3 fatty acids in example diets are predominantly in the form of linoleic acid and α-linolenic acid, respectively and are based on average fatty acid concentrations observed in commonly used feedstuffs
^cEquine Applied and Clinical Nutrition. 2013. ISBN 978-0-7020-3422-0