The cost of hay is high cost but there are methods to decrease hay waste. A paper in the Journal of Equine Veterinary Science out of the University of Minnesota indicated that hay waste was much greater when hay was fed on the stall floor rather than in a feeder, so using a feeder is really important.
However, there are differences in feeders. The ones tested were basket feeders, hayracks, and slat feeders, and these were compared to not using a hay feeder at all and to feeding hay on the ground. Horses fed using no feeder at all wasted 13 percent of their hay so if you are not using a feeder for feeding square bales, you are wasting a lot of hay. Horses fed in slat feeders only wasted one percent of their hay, while horses fed out of basket and hay rack feeders wasted three percent and five percent respectively.
Basically, the feeders that provided less access also had less waste of the hay. Although the slat feeder has the lowest amount of waste, it also decreased the horse's consumption of the hay due to limited access. Feeding without a feeder decreased the amount of hay consumed because of the amount of hay lost as waste. So overall, less feed was consumed using a slat feeder or no feeder, and these horses lost weight. In comparison, horses fed hat out of the basket feeder and hayrack feeders resulted in an increase in hay intake, a slight increase in body weight, and decreased waste. So if you are not using a feeder for your horse, you need to do so. The basket type feeders or hay racks will allow your horse to ingest more of their hay while wasting less of this expensive feed.