Hey! How's he doing? You've had some good replies- I would also make sure he's dewormed and teeth are checked... you can feed high-fat grains which won't hurt him BUT WILL NOT help him gain weight either.

I know I know, america has heard this for a long time...but it's not what makes the tons of fat you see on some horses... try it yourself...lol just kidding! I don't care if you eat a tub of straight lard...your body just won't absorb all the fat like that. It absorbs very little. I've studied health for eight years. Have you ever heard of Dr. Joel Wallach? DVM, MD- He has been a vet for over 25 years and is also a natropathic doctor. He did studies on animals and then to humans for several years and found alot of stuff untrue that america was pushing... carbohydrates such as wheat and white bread...sugar also...is why america has some of the most overweight people. Not too far from animals either...

I fed one of mine this winter who has weight problems...I kept him off of the fat cr*p and fed him all the hay he could eat, along with 12% mixed with wheat flour. Oats is great too. He picked up weight very fast. I've used weight-gain products and also senior feed which has alot of fat in it. That was before I knew that fat isn't absorbed into the body hardly at ALL.
Beet pulp is good for weight gain too. I've said all this because of experience, I hope you don't think I'm saying it because I just heard it from someone else lol!! I'm a critic and I like to make sure something is true before I pronounce it to the world lol!!