https://www.gobobpipe.com/goBobOrangeOxHayConserverBaleFeeder.htm
I have 3 Hay Monster feeders, and I love them! I wish I would have got a picture the other day, I had feed 3 bales in one spot and you couldn't fill the loader bucket with hay.
The key is moving them often. I run cows on corn stalks all winter through spring thaw. I feed a bale or two then move the rings. The cows will pick through what is left.
The big things that really affect hay waste are; Hay quality, strong/hot fences, and making them clean it up.
A neighbor has always complained about how much hay his cows go through. He has hay rings in a concrete feed yard and when there is a 1/3 of a bale left he gives them another bale on top of what is left. He asked me to do chores for a week while they visited relatives. He has just moved a bale for his 13 cows and thought I might have to move 2 while they were gone. Theses are 1,600lb rnd bales. I didn't move any, and when he got back he couldn't believe how I was able to get the cows to clean up their hay.
My cows are BCS 4.5-7 in the winter you don't have to starve them to get them to clean up their hay.