I would really try to get that baby on the momma! I know it can be really difficult to do sometimes, but , frankly, bottle feeding a baby is also very difficult as they need to be fed very frequently! It can be done, but is a LOT of hard work.
Is the momma standing well for the baby to nurse? Sometimes it can take that little foal quite awhile to figure it out, and it is difficult to watch as you find yourself wanting to jump in and help. Be patient and let the little guy nuzzle around. They usually figure it out within 15 minutes to a couple of hours, normally. As long as the momma is standing well, and the little guy is up and trying, they should be able to work it out. The more time the foal spends feeding from a bottle, the more it is going to think the teat doesn't feel right. Only bottle feed often enough to keep the foals strength up, not enough to keep it full. Hopefully it will get hungry enough to figure it out! Best wishes!