With good, tight, full 4x6 bales, I figure 1 bale per 30 cows per day. Or 1 bale will last 1 cow 1 month. I keep hay in feeders full time and unroll hay of better quality also. That way all the cows can have some better quality hay and also have a feeder full to fill up on. I buy some 5x6 bales that I figure 45 cows per bale per day, but that is baled really full and is really good orchard grass, fescue, and clover, so it goes further than some of the other hay. I like the 5x6 because it is so much cheaper and less percentage waste, but not many people use that size baler anymore.