E538
Mycotoxins

1. Fescue Toxicity: When fescue grass is infected with an endophyte (Acremonium coenophiliam), fescue toxicosis occurs. An endophyte is a fungus that is located within a plant. This condition is sometimes called "fescue foot" in cattle. It is thought that tall fescue plants do not become infected with the endophyte, but are actually grown from seeds that are already contaminated with the endophyte. It is thought that about half of the fescue in the United States is already contaminated with endophytes.
   
   Clinical Signs: Unlike cattle, fescue toxicity in horses most often affects pregnant animals. Horses do not typically show the common signs noted in cattle such as fever, failure to gain weight, and lethargy. When a pregnant mare does show signs, they are most always related to the pregnancy. For example, mares consuming endophyte-infected fescue can have prolonged gestation lengths (greater than 345 days). This is probably due to an interference with normal hormone function. Infected mares can also have trouble foaling (dystocia) and other reproductive problems such as stillbirths and decreased to absent milk production (agalactia). The agalactia is probably the most common sign noticed in mares. There is also some evidence that fescue toxicity can cause decreased growth rates in young animals.
   
   Diagnosis: Most cases can be identified by clinical signs and the presence of tall fescue in pastures. The problem can also be identified by testing samples of tall fescue in the laboratory.
   
   Treatment/Prevention: In most cases, little can be done for the infected animal, outside of removing the fescue from the diet. Recent studies using a drug called domperidone have shown some promise by countering the negative effects the fescue toxicity has on a mare. In preventing this problem, herbicides, prescribed burning programs, and specific fertilizing programs can help reduce the amount of fescue in many pastures. These programs vary depending on the region of the country. For example, to promote the production of Bermudagrass instead of tall fescue in the southern United States, Round-up or gramoxone applied in March and April can be effective, particularly when followed by burning. Fertilizing after mid-May will also help. In many regions of the country, fescue pastures are being planted with other types of grasses.
    
2. Aflatoxins: Aflatoxins can be produced from grains (corn and cottonseed) and soybeans infected with Aspergillus, Rhizopus, Mucor, Penicillium, and Streptomyces fungi. Conditions of drought or storm that stress the plant, followed by warm and moist weather, can cause the problem to occur.
   
   Clinical Signs: Common signs of acute toxicosis include bleeding, bloody diarrhea, not eating, weakness, tremors, and death. Abortions and signs of liver damage (fluid build-up, anemia, etc.) can occur with ongoing aflatoxin exposure. If the animal is exposed to lower levels of aflatoxins over a longer period of time, weight loss, poor hair coat, failure to gain weight, and even tumor production (carcinogenesis) can occur.
   
   Diagnosis/Treatment/Prevention: Most cases can be diagnosed by identifying the toxins in feed and/or liver samples. Feeding an animal aflatoxin-free feed and treating for liver problems can help reverse the problem in many cases. Studies show that it can take over 7 days of feeding this aflatoxin-free diet before the liver is aflatoxin-free. Prevention is really the only treatment.
    
3. Fumonisin (moldy corn poisoning or equine leukoencephalomalacia): Fumonisin is a mycotoxin that affects the liver and nervous system in animals. Is also considered to be carcinogenic (tumor producing). Fumonisins are found mainly in corn and corn screenings.
   
   Clinical Signs: Common signs of fumonisin toxicity include lethargy, confusion, sweating, weakness, tremors, blindness, and death. These signs may come on suddenly after consuming high levels of fumonisin over a period of just 7-90 days. Horses with the true equine leukoencephalomalacia will develop damaged areas in the white matter of the brain.