I suggest you try this after your next training ride..be sure it is after a good long ride..
Take whatever mash you would give your horse (I use soaked Beet Pulp with Dynamite PGR-pelleted grain ration) and put about half of what you might normally give him. Soak it before you leave. When you get back, fill the bucket about half way with water and then push hay into this slurpy mash-tasting water. I can almost guarantee he will eat it, and the bonus is he get more hydration. I have taught every horse I have ever ridden to eat this way after every training ride..when I get to a ride, they dive into it. You can mix the mash before you leave on the loop, then dump the water and hay into the bucket when you get to the vet check.
At a ride, I also put a bit of DynaSpark (happens to have molasses in it) into the water..my horses love it!
Good luck..Ranelle (who once won a "fattest horse" award!)
Courage is being scared to death, but saddling up anyway. ~ John Wayne