When feeding from square bales, how much you feed will depend on the size of the bale and the quality of the hay. When we used square bales in our younger days, we calculated a minium of 1/2 bale per day for our horses and cattle. It was good quality prairie hay. Not as good as alfalfa or timothy, but it was still very good hay. Our bales weighed 60-80 pounds, depending of whether hubby ran the baler (made the bales about 60 pounds so mother in law and I could handle them) or father in law ran the baler (in which case the bales ran around 80+ pounds and he didn't care how mother in law and I had to move them - that was our job!)
The horses and cattle both stayed fat all winter, with the cattle getting a few range cubes and the horses getting a small feeding of oats (also home grown).