Mold in livestock hay can be a significant problem, particularly in years where we have had a lot of moisture and humidity during harvest. The summer of 2016 was not overrun with moisture, however, when we have a shortage of hay, many producers are forced to feed less than ideal quality hay and mold can once again become a challenge.
Mold can grow on hay with moisture levels above 14-15%. Mold growth produces heat and can result in large amounts of dry matter and TDN (total digestible nutrients) loss. In some cases, that heating can be enough to cause spontaneous combustion and fire. Drying of stored hay is enhanced by increased ventilation, creating air spaces between bales, and reducing stack size. However, dry hay will draw moisture from humid conditions, particularly on the outer 6-12” of the exposed surface. Any moisture level above 20% on the exposed surface can result in mold growth and levels greater than 30% can result in the stack’s entire surface becoming covered in black sooty mold.
Molds are more of a hazard in non-ruminant animals than in ruminants. Horses, in particular, are noted as being susceptible to moldy forages. Mold can cause respiratory issues such as RAO (recurrent airway obstruction) and is thought to be a contributing factor to COPD (Chronic Obstructive Pulmonary Disorder). This is doubly true if forage is not fed in a well-ventilated area or if it is extremely dusty. Mold can also cause significantly higher rate of digestive upset or colic issues in horses due to the anatomy of their digestive tract. Slightly to moderately moldy hay, (spore counts up to 1 million cfu/gram) is relatively safe if fed to cattle and small ruminants. While cattle are ess affected by mold, certain molds can result in mycotoxins that can cause abortions or aspergillosis. For more information on hay quality contact your local UGA Extension Agent.