Gotcha...then good for you :) If ample amounts of horse feed isn't an option you may consider giving day old bread a shot. I've heard so many people talk about how well that works at helping a horse boost their weight. Commercial feed can really hit the horse chow budget hard...I've got one on Empower Boost right now to help him gain--he's my only difficult keeper.
1. Too much grain is not good for a horse's stomach. More hay is probably a safer and more affective option (I have a hard keeper myself)
2. Why would you recommend something you haven't tried yourself? I personally have never heard of feeding...day old bread.