In recent years, horse owners have been warned against rushing for the jug of corn oil when a beautiful coat is desired or additional calories for weight gain are needed.
The primary reason corn oil has fallen out of favor has to do with its fatty acid profile. Corn oil contains 50 times more omega-6 fatty acids than omega-3 fatty acids. As more is learned about the numerous health benefits omega-3s (anti-inflammatory molecules) have to offer compared to omega-6s (pro-inflammatory molecules), the use of corn oil in combination with concentrates has declined and often substituted with alternative vegetable oils such as soybean and canola.
Essential fatty acids are not produced by the body, so they must be supplied by the diet. Although an ideal ratio has not been identified for horses, concentrate feeds are typically formulated to have a ratio of less than 10:1 (omega-6:omega-3), which helps create a more favorable balance for the entire diet. Fresh and conserved forages contain more omega-3s than omega-6s, but some horses cannot thrive on forage alone, so selecting the appropriate feedstuffs becomes important.
Flax is widely used in equine diets as a source of fat and omega-3s as well as fish oils which ensure essentialfatty acids are directly available for their anti-inflammatory value and other health benefits, including improvements in glucose tolerance, reproductive function, and immunity.
Increased inflammation is a clinical symptom of certain equine conditions, such as Cushing’s disease and inflammatory airway disease. For these horses, diet manipulation of the omega-3:omega-6 ratio is important, as adding corn oil, with its pro-inflammatory omega-6s, only adds insult to injury.
Keep in mind, though, that corn oil is not the devil. If your horse is prone to gastric ulcers or discomfort there may be justification to add a small amount of corn oil to his diet. One study* found that daily supplementation of corn oil, about three tablespoons, resulted in reduced gastric acid output and this may offer an inexpensive way to support gastric health.
*Cargile, J.L., J.A. Burrow, I. Kim, N.D. Cohen, and A.M. Merritt. 2004. Effect of dietary corn oil supplementation on equine gastric fluid acid, sodium, and prostaglandin E2 content before and during pentagastrin infusion. Journal of Veterinary Internal Medicine 18(4):545-549.