Many people wonder how long they have to wait before feeding freshly baled hay. According to Steven Jackson, Ph.D., in a talk given at one of Kentucky Equine Research’s short courses on equine nutrition, the answer may be not at all. Dr. Jackson stated: “I have on numerous occasions gone and picked up hay out of the field in an afternoon and fed it to horses in the barn that evening and have never had any detrimental reactions.” Shocked’
Jackson is referring to hay that has had a proper time for curing/drying in the field before being baled. Exactly how long this is depends on both the type of hay (legumes, like alfalfa, take longer) and the weather conditions at the time. During this curing, the freshly cut grass will lose moisture and any soluble sugars will break down. However, we are talking a matter of days here, not months. Jackson argues, and correctly so, that any hay that produces enough heat after being baled to make you hesitant to feed it doesn’t belong in your barn in the first place. For one thing, it is likely to mold eventually. Another reason is that this continued generation of heat is the cause of “spontaneous” barn fires.
Of course, in real life not too many hays get perfectly field-cured. Hays that are baled before cured will continue the drying and sugar breakdown process. Again, how long this takes will depend on the type of hay and how far along curing was when it was baled. Because it is more difficult for the interior of a bale to dry, curing could take weeks instead of the few days it would take with grass spread out in the field. The only way to tell if hay is safe to feed is to open the bale. If there is no detectable heat go ahead and feed it — whether it is months old or days old.