Well, like I said, maybe I've got the luxury of having more hay available than most people. If feeding hay is a major cost for you, then I suggest exploring the options that might be avaible to reduce the cost of that practice. I know this might not apply to all who read this because this is a Global Forum, but in my part of the world I have been able to form partnerships and alliances with neighbors, friends, mom & pop farms that have slowed down or quit and other active farmers that have given me access to more hay ground than I really need. Much of the land is free for the upkeep and some tracts cut 4 times a year with adequate rainfall.
Keeping the hay trailers stuffed full is more convenient for me because I have several other businesses I run and we don't always have time to fill them up just when they become empty. It also allows me the opportunity to time filling ahead of inclement weather. They can't waste very much anyway because of the design of the trailers we build and use. I don't care if my cows don't clean up ALL the pickings because in the spring I compost the mounds around the hay trailers and feeders and turn that into a product to sell for a profit too. I already have the equipment to do this with and you would be suprised at the market I've developed and the cash that brings in each summer. I feel that with MY cows, they ration themselves to what they need when it is freely available, and much like minerals they won't gorge themselves after being without for a little while. Not to disagree with Dun, as he is a prominent figure here, but I will clean up after my cows (and make a profit on that too) and my cows will never have to go lacking. I prefer them to be full at all times.
That works here, in my situation, just my opinion.