Omega 3 fatty acids are an essential part of the horses diet, however it isn't commonly found in majority of horse feeds. Omega 3 can be added to your horses diet via oils. Oils that contain higher levels of omega 3 relative to omega 6 fatty acids are considered to be less likely to result in muscle, blood vessel, and other cell wall damage when used as an energy source.
It can take as long as 6-8 weeks before the omega 3 fatty acids added to the diet are incorporated into the cell membranes and have a beneficial effect.
I personally use Linseed oil to provide my horses with the extra omega 3 in their diets. Happy Horse = Happy Riding!