I also have two horses, with one being the pig and dominate. I have to definitely recommend that you separate them to feed so the mare can eat in peace. I also think a recommendation of more hay is needed than a few flakes here and there if there is not much grazing and if you excersize them regularly. I also have a round bale for free choice feeding and it seems to work out fine, If not, you can always pull some off and make a separate pile. Good luck. Peggy