Endure Extra Energy Supplement EndurExtra contains a minimum of 50% fat from several sources such as stabilized rice bran, soybean oil, and flaxseed, making it an excellent source of dietary energy. Fat contains more than two times the energy that carbohydrates and proteins do, thereby fueling horses more efficiently. Flaxseed supplies omega-3 and omega-6 fatty acids, including linoleic acid, an essential fatty acid that must be supplied in the diet of horses.