Feeding Moldy Hay
Feeding moldy hay to livestock is a tough decision. Although all hay contains some mold, when mold becomes noticeable the decisions become important. Usually, mold makes hay less palatable, which can result in lower intake or in animals refusing to eat the hay.
Many other problems from mold occur because of mycotoxins produced by certain mold fungi. This also is part of the decision problem since not all molds produce mycotoxins and the amount produced by those that do is unpredictable.
Direct negative affects of moldy hay are difficult to document. Horses may be the most sensitive to mold among common livestock. For instance, mold spores often contribute to respiratory and digestive problems like colic or heaves in horses. Cattle apparently are less affected by mold, but certain molds can cause mycotic abortions or aspergillosis. People, too, can be affected by mold spores. Mold can cause a condition called farmer's lung, where the fungus actually grows in lung tissue. So try to avoid breathing in many of these spores. The best course of action often is to minimize feeding moldy hay to more sensitive animals, like horses or pregnant cows. This may require a keen eye or sensitive nose when selecting hay to feed each day. Mixing moldy hay with other feedstuffs can dilute problems sometimes, but be careful that you don't make your animals sick by tricking them into eating bad hay that they normally would refuse.
Mold is a difficult problem to deal with. Common sense and good observation often are your best decision aids.
Dr. Bruce Anderson, Professor of Agronomy
Agronomy & Horticulture, University of Nebraska–Lincoln, Lincoln, NE