Horse owners and managers should be concerned about mold growth in hay when feeding horses. Unlike ruminants, horses are very sensitive to moldy hay. Large round bales may not be consumed by horses before it molds unless there are adequate numbers of horses eating it. Not all people realize that this can be a hazardous condition. Many assume that the horses will consume the hay quickly enough that it will not be a problem, but this is not always the case.
If new hay is put out before the horses run out of clean hay, they typically will leave the older hay. The problem occurs when horses run out of good, dry hay and are hungry. Feeding hay up and off the ground and/or under cover to keep the hay away from rainfall may be helpful to prevent or delay molding. When the leftover hay deteriorates and becomes questionably safe for horses to consume it, remove it from the area, to be safe.
