About a half an acre a horse, but you can always throw it a flake of hay to make sure. Also, dpeneding on the breed, you can monitor the weight of the horse when you first begin on the field, and see if they are eating just right/too much/too little.
Not exactly sure about in Indiana but i live in Kentucky and where i live it is 1 acre fenced in per horse. I sugest 2 acers fenced in or more per horse because it alows them more room to run and graze. Good luck to you!
1 acre = 40.5 ares
1 acre = 43,560 square feet
1 acre = 4,046.86 m2
Answer: 1 acre = 0.004046 km²
Answer: 1 acre = 6,272,640 in²
1 acre = 40.468564224 are
One acre contains 40468564.224 square centimetres.
1 acre = 43560 sq feet.
1 acre = 43,560 square feet
1 acre = about 4,046.86 square meters
Answer: 1 acre = 43,560 ft²