Mycotoxins are secondary fungal metabolites that pose a significant threat to animal health and productivity and are found in a variety of feedstuffs, including cereal grains, grain byproducts, harvested forages and pasture grasses. The temperature and humidity in the environment influence mold growth and mycotoxin production.
For instance, some mycotoxin-producing molds thrive in cool and wet conditions while other molds prefer hot and dry conditions. The risk for contamination begins in the field prior to harvest and continues through storage and feeding out.
Crops that have undergone environmental challenges such as heat and drought stress, excessive moisture or physical damage (e.g., hail, insects, wildlife) during certain phases of growth present with the greatest risk of colonization by molds that may produce toxins. It is important to note: Not all molds produce toxins, and toxins can be present even when mold is not visible.
Mycotoxins which are generally produced while the crop is in the field include tricothecenes (e.g., deoxynivalenol (DON aka “vomitoxin”), nivalenol (NIV), T-2 toxin and HT-2 toxin, fumonisins (FUM), zearalenone (ZEN), and ergot alkaloids, among many others. In addition, fungal species such as Penicillium spp. and Aspergillus spp. tend to be considered “storage fungi” that can produce toxins including aflatoxins, ochratoxins and a wide variety of others while feed is stored in grain bins or other structures.
What are negative effects of mycotoxins?
The severity of negative effects from mycotoxins in cattle is influenced by a number of factors including the type of mycotoxin, age of the animal, health status, and the duration and degree of exposure. Animals exposed to a high level of mycotoxins or long duration of exposure may show clinical signs of mycotoxicosis, which range widely from reduced intake, poor growth, immunosuppression, impaired reproduction or even death.
Low to moderate levels of toxins may cause subclinical signs that are not readily observable but can still cause poor growth and reproductive performance, leading to economic losses. Furthermore, the co-occurrence of more than one mycotoxin may result in animals presenting with a variety of signs that are more severe than if a single mycotoxin was present.
To effectively reduce mycotoxin risk, it is important to be aware of the feedstuff type and environmental conditions that may be favorable to the growth of fungal species that could produce a mycotoxin that potentially threatens the health of your cattle. Since every mold has its own optimal conditions for growth and toxin production, including temperature and water activity, the incidence of mycotoxins can vary by time of year, weather conditions and plant species. Some major mycotoxin-producing fungi that have been identified and are prevalent in forages grazed by cattle include endophytic species of fungi such as epichloë and neotyphodium as well as multiple fusarium species, which have historically been associated with cereal contamination.
Ergot alkaloids include a broad range of prevalent mycotoxins known to affect beef cattle in many regions of the U.S. Ergots are produced by endophytic fungi that infect susceptible small-grain species including triticale, rye, wheat, barley and oats, as well as many wild cultivated grasses such as fescue, annual bluegrass, cheatgrass, green foxtail, wild barley and wild oat, brome, timothy and wheatgrasses.
Ergot production has been associated with a cool, wet spring followed by a hot, early summer, as well as grasses exposed to excessive moisture or harvested late. Ergots may be found in grazing environments as well as harvested hays or small grains fed in cattle diets. Negative effects from ergot alkaloids, also known as ergotism, include severe vasoconstriction of small arteries leading to gangrene of the limbs and ears, rough hair coat and poor growth and reproductive performance.
Fusarium molds are believed to be produced after stress conditions followed by wet weather during flowering. Each fusarium mycotoxin presents their own negative effects on cattle growth and reproductive performance and, unfortunately, these toxins have been identified in a broad range of native grass species, legumes, cereal grains, grain byproducts and perennial grasses.
Each of the fusarium mycotoxins may display different, overlapping or even exacerbated outward signs. For instance, type A and B trichothecenes are known to reduce gut integrity by inhibiting protein and nucleic acid synthesis, resulting in reduced nutrient absorption and alterations of immune function. Similar to DON, FUM contribute to the disruption of the intestinal barrier and act synergistically in the presence of DON and other mycotoxins, imposing greater negative effects when found in combination than when occurring alone. Zearalenone is frequently found in the presence of DON and other type B trichothecenes and primarily has an estrogenic effect on animals, which can significantly impair heat cycles, embryo survival and cause abortions in cows as well as causing poor testicular development and reduced sperm production and semen quality in bulls.
Fungi belonging to the genus aspergillus and penicillium produce aflatoxins and ochratoxins, among other types of mycotoxins. These toxins can be produced in the field under hot and dry conditions but are also a concern in storage when conditions support mold growth (i.e., adequate moisture and oxygen present). Penicillium molds present an added challenge as they are able to survive and produce toxins under low pH conditions, including in silage. Aflatoxin B1, B2, G1 and G2 are of great concern to human health through direct exposure of contaminated food or indirectly through tissue, eggs, milk or dairy products from animals fed aflatoxin-contaminated feeds.
Aflatoxins also pose a threat to the health and performance of livestock and cause gastrointestinal dysfunction and can reduce weight gain, feed efficiency and milk production. Ochratoxins are less common but are produced by aspergillus and penicillium species in favorable storage conditions and greatly affect kidney function as well as cause liver and intestinal damage.
Mitigating the mycotoxin risk
Mitigating mycotoxins in cattle diets can be a challenge, as you need to identify and quantify the risk of the challenge in order to effectively reduce mycotoxin exposure and prevent negative effects. Since cattle are selective grazers and mycotoxins are not evenly distributed throughout pastures, crops or feedstuffs, obtaining representative samples for testing may be difficult. A highly contaminated sample does not mean the entire lot of feed is bad, and a “clean” sample does not guarantee all of the feed is mycotoxin-free.
Although limitations exist, mycotoxin analysis of feeds can provide useful information to aid in making decisions such as to adjust the inclusion level of the contaminated feedstuff in the diet or if an in-feed mitigation product is justified.
There are a number of clay and yeast products on the market that can bind (adsorb) mycotoxins, but it is important to pair the correct product with the correct mycotoxin. For instance, the chemical and physical properties of the mycotoxin play a big role in determining whether the toxin can effectively be adsorbed by a binder. In addition, binder products vary in their composition and chemical structure, leading to variability in their effectiveness at adsorbing mycotoxins. Aflatoxins and ergot alkaloids are often sufficiently controlled by clay-type binders.
However, zearalenone and trichothecenes are poorly adsorbed and require other methods, such as detoxification through enzymatic activity which alters their chemical structure, thus preventing biological activity of the toxin in the animal. Additional components some products may include are plant and algae extracts that have been identified to repair and reduce damage to the liver and gut as well as provide support to the immune system. Combination products that provide activity through binding, enzymatic degradation, and protective plant and algal extracts can provide broad-spectrum mycotoxin control to combat a variety of types of mycotoxins frequently identified in livestock feedstuffs.
In order to manage the risk of negative effects from mycotoxins in feedstuffs, it is recommended to routinely screen your feedstuffs to understand which types and concentrations of mycotoxins are present, be vigilant of cattle displaying signs of mycotoxicosis (i.e., poor growth, reduced intake, feed refusals, rough hair coat, immunosuppression, reproduction issues, etc.) and work with your nutritionist and veterinarian to determine if a mitigation strategy is needed.
