How long to keep hay?

Hey all, I am wondering how long you should store hay. I bought hay last winter for my horses and stopped feeding in spring when the gr started growing and have some left over. Right now we have them turned out in the irrigated pasture because hay is so expensive but I am wondering how long I can keep the 6 bales I have left in the barn. It is dry and away from elements so would a year be ok or should I just start feeding it to get it out? Thanks!