Reading the "Pellets vs Hay" thread started me wondering about this. Say you're going on a multi-day pack trip with no grazing along the way, so you have to pack all the food for you and your horse. How many days can you go?
For comparison, as a human backpacker, and using freeze-dried & dehydrated foods (finding water along the way), I could pack for a week easily, maybe two at a stretch. If I had to carry my water, maybe three days max.