As long as it is dry and unsoiled, it is okay to keep. If loose hay sits in a pile too long it may get dusty, so clean it out if it gets to that point, but there is no set expiration date on left over hay. If the hay is sheltered from the elements it will last longer. If it is outside in the weather, it should be replaced at least every few days, to prevent mold growth. Basically just use your best judgement. If it still looks fresh, keep it, if not, pitch it.
Last edited by kiltsrhott; 05-26-2014 at 12:11 AM.