Fattening up a Horse

I have a yearling I have been trying to fatten up. I think I've found the perfect mix, as it seems to be doing the trick. I use pelleted timothy hay (soaked in water), milk replacer (yes even with a yearling), cool calories, and a blend of oil (corn, canola, olive, soy, and cocoa). She is a picky eater, so many tricks haven't worked because she refuses to eat them. But.... This seems to be the perfect "mash" for her.