Weanlings fed rain-damaged and moldy alfalfa gained less weight and had less wither height gain than those fed undamaged hay. The moldy hay was of lower nutritional value. Horses are prone to respiratory problems that become more serious in winter. Inadequate ventilation in stalls results in poor air quality. Hay and bedding are major sources of dust in a stable.
All hays have some mold spores.
Mold spores are the most common cause of inflammation and irritation of the horse's small airways. Wetting or soaking hay reduces a horse's exposure to molds. Be sure to only wet one hay feeding at a time. Straw bedding contains higher levels of small, respirable mold spores than other bedding materials. Horses kept outside with adequate shelter are less likely to have respiratory problems.