Tried FB on Premierflex HA. I thought he improved but couldn't say for sure so I didn't buy anymore. He then got a lot worse, so I bought some more, loaded him up again and he is definitely much, much better with it than without it.
I have a feeling that the quantity of cod liver oil you would need to feed would be pretty high for an animal as big as a horse and many horses will not tolerate a lot of oil in their diets, plus it is an animal based product (not natural for horses).
I think that soaked linseed contains a lot of the omega nutrients, but I'm sure someone else on here will give you the details about that as I really have no idea.
I look after an 18yr old mare who has arthritis in both hocks, shes been on NAF Superflex since March and there is a definite improvement since feeding it.