Mycotoxins have been a prevalent problem in U.S. grain crops for the past several years thanks to the perfect timing of wet conditions that they thrive under. U.S. food safety rules are very effective at keeping these toxins out of the human food supply but they pose an ongoing threat for livestock producers. Mycotoxins tend to begin in the field but the right conditions can spur their occurrence at any point through harvesting, handling, storage, and processing. Poor storage practices tend to increase already existing levels. Temperature, moisture, and humidity are the main factors for their growth and development.
These toxins are actually the residue of deteriorating mold, like the poisonous byproduct of a fungal infection. Fusarium and Aspergillus mold strains account for the majority of toxin problems. Not all moldy grain will end up contaminated with poisonous residue but even trace levels of some of these toxins can be harmful to livestock. And as livestock producers know all too well, the regulatory limits on mycotoxins don’t necessarily protect animals from negative effects. Regulatory limits don’t even exist for some harmful mycotoxins, and new and different strains are being found all the time.
Most mycotoxins can remain stable for years in feeds, and many survive ensiling and food processing. They can be concentrated several-fold in cereal by-products and typically concentrate threefold in distillers or corn gluten co-products. Feedstuffs are usually contaminated with a mixture of different mycotoxins. It is known that multiple contamination may impair the performance of highly productive animals. Many studies have indicated that there is often a synergistic effect of combined mycotoxins. Scientists estimate that there are 300 to 400 mycotoxins presently identified with more being isolated as new techniques and processes evolve. Below is some detailed information about the five mycotoxins that are most prevalent U.S. grain as well as some charts from BIOMIN’s latest World Mycotoxin Survey showing contamination prevalence in this year’s samples:
Aflatoxin: Aflatoxins are poisonous carcinogens and mutagens that are produced by certain Aspergillus molds. They are regularly found in corn, soybeans, wheat and other staple commodities. Corn silage can also be a source of aflatoxins. Animals fed contaminated food can pass aflatoxin transformation products into eggs, milk products, and meat. Dairy farms are generally the most concerned about aflatoxin levels as allowable levels for dairy cows (<20 ppb) is lower than that for beef (<300 ppb). All animals are susceptible to aflatoxins, but the sensitivity varies between species. Young animals and monogastrics are more at risk for toxicosis. Signs in ruminants include reduced performance, signs of liver damage, reduced immune function, abortion, and death. In swine, young nursing or weaned growing pigs are much more susceptible than adults. When aflatoxin is ingested by a lactating dam, toxic metabolites are passed in her milk, exposing the nursing pigs. These toxins reduce feed intake, average daily gain, and feed efficiency. Since aflatoxins are immunosuppressive, signs of toxicosis often include an increase in previously controlled secondary diseases.
Fumonisin: Produced principally in corn by Fusarium molds, fumonisin is known to cause equine leukoencephalomalcia in horses and pulmonary edema in pigs that eat contaminated feed. At levels well below those needed to cause hepatic lesions or pulmonary edema, fumonisins are likely to reduce growth rates and increase disease in pigs. If horses are already showing neurologic signs or pigs are demonstrating evidence of respiratory distress, the prognosis is poor.
Deoxynivalenol (DON): Commonly called vomitoxin, DON is produced by several molds in the genus Fusarium, especially F. graminearum, which causes Gibberella ear rot of corn and head blight (scab) of wheat. Fungal infection of the cereal grain typically occurs in the field, and its presence is commonly associated with times of heavy rainfall and high humidity and delays in harvesting the crop. It remains stable during storage, milling and processing, and is, at least to some extent, resistant to thermal processing of both food and feed. The mycotoxin at first causes reduced feeding by the animals and, thereby, slower gain or loss of weight. At higher concentrations of the mycotoxin, the animals are induced to vomit and totally refuse to eat. Swine and other monogastric animals show the greatest sensitivity.
Ochratoxin (OT): Also known as OTA, it is formed by the mold of the Aspergillus and Penicillium species. It is predominantly found in grains, nuts, legumes, coffee, spices and dried fruit, if the food was not dried sufficiently prior to storage. The toxin can accumulate in the organs of the animals that are fed with contaminated feed which further contaminate the products derived from them, such as milk and meat-based products. Ruminant animals are more resistant than monogastrics to OTA toxicity. In general, exposure to OTA contaminated feed reduces animal growth rates and affects animal production. Pigs are generally considered as the animal species most sensitive to the nephrotoxicity of OTA. Turkeys, chickens, and ducklings are also susceptible to this toxin.
Zearalenone: Also known as RAL and F-2 mycotoxin, this is a potent estrogenic metabolite produced by some Fusarium species that cause ear rot in corn and head blight in wheat and barley. Zearalenone is produced by the same fungi that produce DON, in the same crops, and usually at the same time. Typically, zearalenone concentrations are low in grain contaminated in the field, but increase under storage conditions with moisture greater than 30%–40%. The most obvious problems are seen in pigs: doses as low as 1–5 mg/kg can induce vulvovaginitis and vaginal and rectal prolapse in young female pigs. Sheep and cattle are more resistant, and it seems likely that rumen microorganisms are responsible for metabolizing zearalenone to compounds of lower toxicity. Chickens are also comparatively resistant, tolerating up to 30 mg/kg of zearalenone in feed.
