How can I get weight on my elderly horse?

codyskeeper Asked: How can I get weight on my elderly horse?

I have a 28 year old paint horse gelding that is in good shape and gets ridden lightly once or twice a week and still enjoys it. The problem is I cant seem to keep weight on him! He is not deathly skinny or anything but you can see a few ribs and I dont like it.
In the morning I feed one large coffee can scoop of 12% pellet feed and 2 scoops (scoop that came with it) of Farnam weight builder for horses. I soak it all in lots of warm water to make a mash so that he can eat it because he doesnt have very many teeth left (cant chew hay so I feed alfalfa pellets).
At noon I feed large coffee can scoop of alfalfa pellets that have been thoroughly soaked in hot water for about an hour.
At night he gets fed one large coffee can scoop of 12% pellet feed also soaked in warm water.
Sometimes I will give him a little hay but he cant chew it very well and it just balls up and he spits it out. He always has fresh water available and is on a regular deworming schedule.
He is fed separately from my other horse so she doesnt chase him off him feed.
Other things I have tried that didnt work-
Upping feed to 2 scoops two times a day (made no difference over a 3 month period)
Tried feeding a little rice bran (gave him diarrhea)
Tried feeding Purina Amplify supplement for 2 months (didnt work)
Im sure Im forgetting something else that I have tried LOL!
Any ideas will be greatly appreciated! Thanks!