Hay, Molds, and Feeding Problems in Montana
All hay contains molds, but not all molds are directly dangerous to livestock.
2016 Winterby Barry Jacobsen
Associate Director, Montana Agricultural Experiment Station and Emeritus Professor of Plant Pathology, Montana State University
Molds in hay can affect animals by infecting them, producing mycotoxins (or changing natural plant compounds to toxic compounds), producing allergic reactions, and, ultimately, reducing the palatability and nutritional value of the hay.
Mold problems in hay can result from infection of the forage before cutting. A common example is ergot, which is caused by a fungus that infects the floral organs of grasses at or near the time of flowering. Ergot is typically a problem when cool, wet springs favor infection by the ergot fungus. The small black ergot sclerotia (i.e., black, hard bodies varying from the size of the grass plant’s seed up to ½ inch, depending on the grass) can be found in the heads of all grasses. When ingested by animals, it will cause ergotism, which is characterized by skin necrosis (i.e., death of cells), rough hair coats, necrosis of the ears or tail, lameness or loss of extremities, poor milk production, and poor weight gain. When these symptoms are visible, hay should be examined for the presence of the small black ergot sclerotia that resemble rodent feces.
Fescue toxicosis, caused by alkaloids produced by fungal endophytes (i.e., fungi organisms that live between plant cells) of forage grasses, can also cause problems similar to ergot poisoning. In Montana, grasses infected with endophytic fungi, particularly tall fescue, have been identified, but a case of fescue toxicosis has never been observed. This is most likely because the problem is typically associated with pure stands of tall fescue and in Montana, mixed species of grasses are more common in pastures and hayfields.
Slobber syndrome, another issue related to moldy hay, is associated with Rhizoctonia infection of red clover and a few other legume forages. The Rhizoctonia fungus produces the mycotoxin slaframine which, upon ingestion, causes excessive salivation. This problem is not common in Montana, but is much more common in the Midwest and adjoining portions of Canada.
Once hay is cut, molds, including yeasts, will grow until moisture is less than 14-15%. The most common fungi associated with moldy hay are members of the fungal genera and include Alternaria, Aspergillus, Cladosporium, Fusarium, Mucor, Penicillium, and Rhizopus. As these fungi grow, they produce heat and moisture as they break down plant tissues, which, ultimately, can result in spontaneous combustion of haystacks under certain conditions. The temperature, moisture content, and duration of moisture content above 15% will determine the extent of mold growth. Depending on which molds predominate in a hay source, there may or may not be mycotoxins present. Analysis of moldy hay samples, particularly those showing heat damage, will show lower levels of total digestible nutrients (TDN) and lower levels of vitamins A, D3, E, K, and thiamine availability, creating an immediate loss of nutritional value in moldy hay. A second effect is that mold spores can cause allergic reactions and symptoms resembling human asthma in both horses and cattle. Production of mycotoxins by molds that can cause direct toxicity or suppress the immune system are members of the genera Alternaria, Aspergillus, Fusarium, and Penicillium. While Mucor species do not produce mycotoxins, they, along with some species of Aspergillus, can cause mycotic abortion when they infect cattle.
Every year, MSU receives samples of moldy hay with questions regarding feed safety, colic, abortion, poor performance, or even death. Frequently, these samples have been submitted to a lab and a mold spore count is reported. Labs will discuss livestock feeding risks based on mold spore counts. While this might be useful in addressing potential for allergic reactions, it is the mold species present that is critical in determining mycotoxin risk - not the total mold count.
To determine mycotoxin risk, it is important to determine what mold species are present. If Aspergillus or Fusarium species are present, there are laboratory tests that can determine levels of some common and specific mycotoxins such as aflatoxin, T2, DON, and Zeralenone. Unfortunately, there are few laboratories that can do specialized determination of mycotoxins produced by Alternaria and Penicillium species. It is likely that multiple mycotoxins from a single species or from multiple species can be present and their effects can be additive or even synergistic. Representative samples can be sent to the Schutter Diagnostic Lab at Montana State University for determination of fungal species present. If mycotoxigenic fungi are present, diagnosticians can suggest laboratories where actual mycotoxin content can be determined.
Determining the risk of mycotoxin poisoning from moldy hay can be very difficult and often can only be implied following a veterinary pathologists’ report or observation of the symptoms expressed on the animal(s) in question. Diagnosis can be further complicated by the fact that the suspect hay has typically already been consumed, making sample availability minimal.
Symptoms associated with feeding moldy hay include, though are not limited to, feed refusal, allergy symptoms similar to asthma (e.g., heaves or recurrent airway obstruction in horses or interstitial pneumonia in cattle, also known as “Farmers Lung” in humans), reduced feed intake, poor weight gain, colic in horses, diarrhea, lower fertility, abortions, lethargy, poor hair coats, increased water consumption, estrogenic effects such as unexpectedly swollen nipples and vulva, poor kidney or liver function, lameness, and vaccine failure, among other serious problems. It is important to remember that allergies and health problems associated with mold spores also affect people, not just livestock. When working around moldy hay, wear a mask capable of excluding 5 to 10 micron particles.
Where hay or straw has been flooded or kept above 90% moisture, the Stachybotrys species can grow and produce mycotoxins in straw or be associated with inhalation of the black mold spores they produce. This is one of the key fungal species responsible for “building sickness.” These mycotoxins affect humans and most warm-blooded animals. Strachybotyrs symptoms include dermatitis, fever, various chest and upper airway symptoms, inflammatory disorders of the mouth, rhinitis, conjunctivitis, and neurological disorders. Generally symptoms start within two to three days of exposure. Without new exposure, symptoms may last for three weeks or more.
Determining whether moldy hay is safe to feed depends on several factors, including:
- Species: Ruminant animals are generally less sensitive since many mycotoxins are broken down in the rumen. Horses, which are cecal digesters, are considered to be the highest risk.
- Reproductive state: Pregnant animals and young animals are at higher risk.
- Nutritional status: Animals in poor condition are more likely to be affected.
- The dose: The dose makes the poison. Consider what proportion of the ration moldy hay comprises and what the level of mycotoxin present is. If feeding moldy hay, consider spreading the hay out on the ground so that animals avoid the moldy portions while consuming good hay.
- Total digestible nutrient (TDN) content of hay: The higher the TDN, the lower the chance of nutritional problems associated with moldy hay.
Other livestock problems that can mimic mycotoxin intoxication are the presence of toxic plants incorporated into the hay or the presence of toxic seeds. One common example is the presence of dodder seeds in hay. Dodder is a parasitic plant that will appear in field as yellowish or golden-colored string-like vines that produce numerous tiny seeds from midsummer to fall. Ingestion of these seeds will cause colic in horses. It is always a good idea to survey fields for poisonous plants or dodder before cutting.
If you have questions about mycotoxins or are concerned about moldy hay, contact Barry Jacobsen (bjacobsen@montana.edu), the Schutter Diagnostic Laboratory (http://diagnostics.montana.edu/) or your local MSU county or reservation Extension office.