Alpha Linolenic Acid (Omega 3) and Linoleic Acid (Omega 6) are Essential Fatty Acids meaning they must be supplied in the diet. Oleic Acid (Omega 9) can be manufactured in the body. These fatty acids are important in the production and maintenance of cell membranes and also act as a source of lipid mediators involved in the synthesis of chemicals which control the inflammatory response including Prostaglandins, Thromboxanes and Leukotrienes collectively called eicosanoids. These are incorporated into cell membranes where they can influence the structural character of the membranes and how they respond to insult like trauma or infection. Eicosanoids derived from the Omega 6 fatty acids provide a stronger inflammatory response to insult than the weaker response generated by the Omega 3 family of eicosanoids. Ultimately the balance between the two determines the inflammatory outcome.
The natural diet of the horse is high in Omega 3 and lower in Omega 6 FA’s. Grass pasture has around 9-11g/kg DM Omega 3 but only 4g/kg DM Omega 6 or in other words an Omega 3: 6 ratio of approx. 3: 1. This balance is reversed in grains where in oats for example the Ratio is 1: 23 and corn even worse at 0.7: 21. The only seed with a positive Omega 3: 6 ratio is flaxseed at 228g Omega 3 to 59g Omega 6, a ratio of almost 4: 1.
As the natural grazing diet has been replaced by grain based diets for working horses, the Omega 3 intake has declined, and the Onega 6 intake simultaneously increased. This change in the ratio favors a more reactive inflammatory environment in the body with potential to promote chronic, long term or low grade inflammation. The idea behind supplementing Omega 3’s is to redress that balance in performance horses on grain diets and in so doing, to reduce the pro-inflammatory influence of the balance between Omega 3 and Omega 6.
Precise requirements for Omega FA’s have not been established for horses, but from other species we expect requirements would be comfortably met by horses on pasture diets. The best ratio between Omega 3 & Omega 6 is also unknown and it is likely that the intake quantity as well as the ratio influence the inflammatory response result.
Experiments to assess the effect of Omega 3 supplementation have given mixed results. For example, one trial showed decreases sensitivity to mosquito bites (Queensland Itch) in supplemented horses, but another similar trial showed no difference compared to controls. Omega 3 oils, usually flaxseed and fish oils, are often used as joint supplements, probably due to some human studies showing benefits in Rheumatoid Arthritis, but the Osteoarthritis in horses is a very different disease process and the limited experimental work has failed to show a clear beneficial reduction in clinical signs of pain and lameness scores. Further studies are needed to confirm the value of Omega 3 supplementation or lack of it.