Barring the ulcers, nerves, stress etc.that was mentioned above, if it just a case of the foal not liking grain products, I have found that if you just take a little handful and stick it in their mouths several times a day, they will get to liking it. You have to make sure you are actually getting it in the mouth, don't just offer it by hand. Obviously, not a big ol' mouthful they will choke on, but just a tablespoon or so. At first they will go to great lengths to spit every single morsel of it out. After a few times, or a few days of doing this they get a taste for it and you never have to worry about it again! I have actually had two different foals that wouldn't touch the stuff, even when their momma was chowing down on it. This is how I got both of them to start eating it. Good luck with it. I know weaning time can be stressful for EVERYONE sometimes.