Just a little tip -- a lot of the muscle-building products for horses contain gamma oryzanol, which is a substance found in rice bran oil. So, it would probably be cheaper just to feed rice bran oil. If your local feed store doesn't carry it, ask them if they will order it for you so you don't have to pay for the shipping. Rice brain oil is pretty cheap, but the shipping is what kills you! A few years ago, I was riding a horse that really needed to build muscle, and I asked my local feed store if they would start stocking rice brain oil for me -- they were more than happy to accommodate me. I saw great reults with it (although, like Nicole said, proper exercise is also key).