Strategy by AFK nutrition or do having touch threw master feeds
We add corn oil to some of our horse's grain
Ric bran works great and I've never had a horse that wouldn't eat it.
Rice Bran and cocosoya (coconut and soy oil) are great high fat supplements
Maybe the food irritates his stomach could have ulcer or any type of blistering in his mouth could always try mashing the food by adding water to it
Should add that I am in Canada!