Oh wow. 5 bags! Luxury!
When I was at CARD every stall, except one, got 1/2 bag every morning. They were pretty much emptied after mucking, and with a tight budget and all *shrugs*. The horses were out nearly all day, but I don't recall seeing any of the horses ever laying down in the stalls.
There are mats in all the stalls too. I think they were completely changed weekly.