Do not feed moldy hay

Do not feed moldy hay

Do not feed moldy hay

When purchasing lower quality hay for cows or horses, be careful the hay does not contain mold. Grey or black hay is an indication of mold and should be avoided at all costs. Take a bale apart to check the inside; black sections of mold inside the hay indicate bad baling or storing procedures. Mold makes hay less palatable, resulting in lower intake or in greater animal hay refusal. Many other problems from mold occur because of mycotoxins produced by certain types of mold fungi. Be cautious as you prepare to feed, but if you see mold in your hay, keep in mind that not all mold produces mycotoxins, and the amount produced by the different types of fungi is unpredictable. 

Molds commonly found in hay include Alternaria, Aspergillus, Cladosporum, Fusarium, Mucor, Penicillium, and Rhizopus. Horses are more sensitive to mold then other species of livestock. Mold spores can cause respiratory conditions such as, Recurrent Airway Obstruction (RAO) like heaves and digestive problems like colic. Cattle can generally tolerate and eat a little mold without problems, but keep in mind that some types of mold may cause mitotic abortion or aspergillosis. People handling moldy hay should avoid breathing in the spores since they can grow in the lung’s tissue causing a condition called farmer’s lung.

A horse with heaves will have a normal temperature and a good appetite, but will often have decreased exercise tolerance, coughing and nasal discharge. Labored breathing occurs during exercise and, in some cases, while at rest. Hypertrophy (increase in the size of muscles) of the abdominal oblique muscle used for breathing creates the characteristic ‘heave line’ seen on horses with RAO. Some horses are highly allergic to certain mold spores while others seem to be minimally affected. Even among horses with symptoms of RAO, can be variations of their sensitivity levels to additional detrimental stimuli such as dust and poor air quality. To decrease exposure, horses should spend more time outside on pasture rather than on a dusty paddock or inside the barn. Additional ways to reduce dust exposure are as follows:

• Do not feed dusty and moldy hay and grains.

• Place feed at a lower level so particles are not inhaled through the nostrils.

• Feed hay outside to minimize dust problems. In severe cases, hay may be replaced by hay cubes.

• If the horse is housed indoors, ensure that there is good, draft-free ventilation through the stable. 

Sometimes mold spores are counted on moldy feeds to obtain an indication of the extent of molding and relative risks in feeding them. Table 1, contains classification of risks at various mold spore counts.

While most molds do not produce mycotoxins, the presence of mold indicates the possibility of mycotoxin presence and animals being fed moldy hay should be watched carefully for mycotoxin symptoms. These symptoms may include: Intake reduction or feed refusal; Reduced nutrient absorption and impaired metabolism, including altered digestion and microbial growth, diarrhea, intestinal irritation, reduced production, lower fertility, abortions, lethargy, and increased morbidity; Alterations in the endocrine and exocrine systems; Suppression of the immune system which predisposes horses to many diseases. A suppressed immune system may also cause lack of response to medications and failure of vaccine programs; Cellular death causing organ damage.

If hay is dusty, take care in feeding to sensitive animals and those, especially, in areas with poor ventilation. If hay is moldy, the recommendation is to not feed it to horses at all. If symptoms of mycotoxin poisoning are observed (which can occur from mold not visible), check with a nutritionist to make sure the ration is properly balanced and with a veterinarian to eliminate other disease/health problems. Quick test kits (ELISA kits) are available to determine presence of mycotoxins but they can give false positives. Some forage testing laboratories will provide other mycotoxin tests. Often, the best strategy is to remove a suspected mycotoxin-contaminated feedstuff from the diet and see if symptoms disappear. If mycotoxins are present, the feedstuff can often be fed at a diluted rate and/or with approved feed additives.


Monitoring Mold When Feeding Hay, Rocky Lemus, Extension Forage Specialist

Moldy Hay for Horses, Dan Undersander, University of Wisconsin (