Mycotoxins are toxic chemicals produced by fungi. Various health challenges may occur in animals and humans when high enough levels of mycotoxins are ingested through contaminated foods. Both ruminant and non-ruminant species are at risk for mycotoxicosis – the illnesses that develop as a result of ingesting mycotoxins.
The presence of mycotoxins indicates that there has been fungal contamination in feedstuffs. There are many dozens of mycotoxins that have been identified but only a handful – those that are most common in animal feedstuffs – have been studied to a large enough extent to know how they affect animal and or human health. Mycotoxins are usually present only in microscopic amounts, being measured in parts-per-million (ppm) and parts-per-billion (ppb).
It’s important to understand that although mycotoxins are produced by fungi, not all fungi produce mycotoxins. Mold, also a member of the fungus family, tends to get the most blame for mycotoxins in animal feeds. Fungi and molds usually grow in warm, moist and humid conditions. The exact circumstances or growing conditions in which fungi produce mycotoxins is not well understood.
Mycotoxins have been around since the beginning of time. However, they began to be identified as problems in the 1960s. Prior to the emergence of globalized agriculture, issues with mycotoxins were most likely isolated and limited to short time periods and small geographic regions. A crop or a storage facility, for instance, may have developed mycotoxins for a season but would disappear as crops were rotated and storage facilities were emptied and cleaned. As commercial farming incorporates more monoculture and agriculture becomes more globalized, the prevalence of mycotoxins in the food supply has increased.
Modern animal agriculture uses grains and grain byproducts as a primary food source. Dairy cows are routinely fed diets consisting of corn, barley and wheat-based ingredients. Due to the abundance of carbohydrates, all grains are susceptible to mold growth and the production of mycotoxins when conditions are favorable. Mycotoxicosis and other metabolic challenges occur when diets contain grains and byproducts that are heavily contaminated with mycotoxins.
Feeds contaminated with mycotoxins can cause a variety of illnesses in dairy cows and young stock that may result in poor milk production, poor growth rates, poor fertility or abortions and lead to death when organs such as the liver or kidneys are seriously affected. In all cases, depending on the type and severity of mycotoxin contamination, the animal’s defense mechanisms and immune system will fight to mitigate the problems caused by mycotoxicosis.
Mycotoxins are highly resistant to degradation or destruction during processing or storage. Mycotoxins can also develop during storage even when none was present during growth. Despite processing and heat, corn byproducts such as distillers grains (DDG) and corn gluten will also remain contaminated with mycotoxins if the original corn grain was contaminated. Adverse storage conditions with high heat and humidity have been known to produce mycotoxins, as fungi are produced during storage.
Corn – including corn silage – is the most widely grown crop in the U.S. and is a primary feedstuff in dairy cow diets. Corn is highly susceptible to mold growth as it grows. Mold grows on the ears, on the leaves and on the stalks and remains there during harvest, transportation and storage. However, depending on the moisture, humidity and temperature during all stages of growth, corn may or may not develop mycotoxins in any given season.
The mycotoxins, deoxynivalenol (also known as DON or vomitoxin), fumonisin and zearalenone all come from a fungal species called fusarium and are known to be problematic for dairy cows as well as monogastric species. Mycotoxicosis in farm animals is often difficult to diagnose and treat effectively. There are great differences in the susceptibility of mycotoxicosis in animals, depending on species, age and sex. Mycotoxins have an immunosuppressive effect, although the exact target within the immune system may differ. Many are also cytotoxic meaning they can do direct damage to the gut, skin or lungs. Presence of multiple mycotoxins may be synergistic, increasing the susceptibility of the exposed animal to other infectious diseases.
Feedstuffs such as DDG or corn gluten have long been used for protein and energy supplementation in dairy cow diets. Hominy, another corn byproduct, is often used to supplement diets that are low in energy. All of these products have proven nutritional value but can still be problematic if contaminated with mycotoxins. Mycotoxin contamination in corn is nearly unavoidable and it’s difficult to find a crop of corn that does not contain a mycotoxin. In the U.S., the mycotoxin, aflatoxin, is the only mycotoxin that is regulated by the U.S. Food and Drug Administration. Aflatoxin B1 has been identified as a potent natural carcinogen and is routinely monitored in grains and is commonly found in peanuts as well as cottonseed, a product used by the dairy industry. Aflatoxins appear to be more prevalent in feeds that have been grown or stored in hot, moist and humid conditions.
Feed manufacturers and other feed handlers are required to regularly test for aflatoxins to ensure that levels do not exceed legal limits. Other common mycotoxins such as DON should also be tested on a regular basis because they pose significant health problems for all species (see table). Dairy farmers who suspect they may have mycotoxin issues in their herd should verify with their feed supplier that the feeds they bring in are regularly tested and those tests are well below dangerous levels. Once again, it is nearly impossible to find feeds that do not have at least some minute level of mycotoxins in them.
Mycotoxins in dairy feeds do not just affect corn. Other grains such as wheat, rye and barley also are susceptible to mold growth. Each of these grains can support mold growth when growing conditions are optimal. Although fungicides may be effective in decreasing fungal growth in plants, a more environmentally friendly way to limit fungi is through crop rotation and avoiding monoculture farming.
In the case of DDG or wheat byproducts such as mill run, it’s difficult to identify mycotoxin contamination with a visual examination. Laboratory testing is the most effective way to determine if plants are contaminated and what types of mycotoxins are present. Most forage testing labs offer mycotoxin testing for a number of the most commonly found mycotoxins. The key to avoiding mycotoxin contamination is to purchase feeds from reputable suppliers that test for mycotoxins on a regular basis.
There are now a number of different mycotoxin absorbents or binders available. Some are clay based (for example, aluminum silicate) and others are carbohydrate based (for example, oligosaccharides). All of these products form chemical bonds with various mycotoxins, rendering them ineffective in the animal gut. Depending on the level of contamination, problems may still persist even if binders are included in the diet. Research is ongoing to find binders that bind with specific mycotoxins. One type of binder may be more effective on certain types of toxins whereas another binder may be more effective on other toxins. In today’s dairy diets it’s always prudent and precautionary to keep a binder in the diet year-round. Check with your feed supplier or an animal nutritionist for more information.
Unfortunately for animal agriculture, mycotoxins are a growing concern as agriculture becomes more globalized and feeds are being imported and exported more frequently around the world. Knowing the geographic origin and the growing conditions of feeds and byproducts and testing of feeds is the best way to avoid mycotoxin contamination in animal feeds.
Read more: Mycotoxins and Binders