Mycotoxins are toxic secondary metabolites of molds, primarily produced by species of the Aspergillus, Penicillium, and Fusarium genera. Depending on weather conditions during the growing, harvesting and post-harvest season, livestock feed — particularly grains — can become susceptible to mycotoxin growth and infestation.
Due to their toxicity, mycotoxins pose severe health risks for both humans and animals. Symptoms of mycotoxicosis vary by species and range from dermal lesions and decreased growth to organ failure and death. Thus, their presence in livestock feed is monitored through federal regulations that set maximum tolerance levels based on the species, age, and production stage of the animal(s) to be fed.
In a global survey of mycotoxin prevalence, 77% of the North American livestock feed ingredient samples tested positive for the presence of at least one mycotoxin above the threshold level. Therefore, in any livestock feeding system, it is imperative to understand the threat that mycotoxins pose to animal health and implement proper monitoring and management procedures to reduce the risk of mycotoxicosis.
Before delving into mycotoxin management, it is important to understand the characteristics of commonly occurring mycotoxins, such as the fungi genera from which they are produced, feed material with the highest risk of infection, and ideal conditions for growth. Although over 400 mycotoxins have been identified, we will focus on the five most common categories of mycotoxins in feed manufacturing, which include aflatoxins, ochratoxins, trichothecenes, fumonisins, and zearalenone.
Aflatoxins include Aflatoxin B1, B2, G1, and G2, which primarily are produced by Aspergillus flavus and Aspergillus parasiticus. Aflatoxin B1 is the most common of all the aflatoxins and is also the most potent, being listed as Group 1 human carcinogen by the International Agency for Research on Cancer. Growing conditions that promote the growth of aflatoxins in field grains include warm ambient temperatures ranging from 24°C to 32°C and little to no moisture. Thus, geographic locations with hot and dry climates are more susceptible to aflatoxin infestation in grains, especially if the integrity of the grain has been compromised by insect damage. Raw feed grains that may be susceptible to aflatoxins include corn, sorghum, soybeans, wheat and barley. Animals consuming aflatoxin-contaminated feeds are likely to experience liver diseases as the liver is the primary target organ of aflatoxicosis. The US Food and Drug Administration (FDA) has determined aflatoxin in corn should not exceed 100 ppb for mature poultry or 20 ppb for chicks.
Ochratoxins are unique in that they are produced by species of both Aspergillus and Penicillium, with ochratoxin A being the most common of the ochratoxins. Growing conditions that promote the growth of ochratoxin A are not fully known, so it is commonly regarded as a mycotoxin that grows under improper storage conditions. Raw feed grains that are most likely to be contaminated by ochratoxin A are barley, oats, wheat, and rye, and animals consuming ochratoxin A-contaminated feed are likely to experience renal failure and intestinal necrosis.
Trichothecenes are Fusarium toxins and are categorized into four types. Type A and Type B are the most common and are differentiated by the presence or absence of a carbonyl group at the C-8 position of the molecular structure. Type A trichothecenes include T-2 toxin and HT-2 toxin, which are the most toxic trichothecenes. Growth of T-2 and HT-2 toxin is optimized in colder climates with temperatures ranging from 6°C to 24°C. Toxic effects of T-2 and HT-2 toxins include digestive disorders and immune suppression. There are currently no regulations for monitoring the concentrations of T-2 or HT-2 toxins in livestock feed.
Type B trichothecenes primarily are represented by deoxynivalenol (DON), also known as vomitoxin. Similar to T-2 and HT-2 toxin, DON is cultivated in cool, moist conditions. Unlike the Type A trichothecenes, DON is much less toxic in comparison and must be present in high concentrations to have a toxicologic effect in poultry. Even so, DON is highly prevalent in corn, sorghum, barley, oats, soybeans and wheat, which is why the FDA has regulated its presence in livestock feeds. Regulations state that DON concentrations in grain and grain byproducts for poultry should not exceed 10 ppm to avoid any deleterious consequences of DON toxicity.
Fumonisins, such as fumonisin B1, B2, and B3, are most commonly produced by Fusarium verticilliodes (formerly F. moniliforme) and Fusarium proliferatum. It is believed that drought followed by warm, wet weather at harvest may be responsible for the proliferation of fumonisins in field grains, specifically corn and sorghum. Fumonisin toxicity is likely to result in liver failure and immunosuppression in broilers. To minimize the risk of fumonisin toxicity, the FDA has determined that broilers, breeders, and chicks should not be fed corn or corn byproducts containing greater than 100, 30, or 10 ppm fumonisin, respectively.
Zearalenone is commonly produced by Fusarium graminearum and can infect grains when field conditions are cool and moist, similar to the trichothecenes. Zearalenone is most notable for its effects on reproduction in poultry because it is similar in structure to estrogen, which can lead to hyperestrogenism as zearalenone competes with estrogen for receptors. Raw feed grains that are likely to be contaminated with zearalenone are primarily corn but also include sorghum, barley and wheat. To date, there have been no regulations enforced concerning the concentration of zearalenone that is acceptable in livestock feed.
Of all the mycotoxins discussed, DON is the most prevalent in North America and is detected in approximately 83% of feed ingredients, followed by zearalenone (60%), fumonisin (57%), aflatoxin (5%), T-2 toxin (5%), and ochratoxin A (3%). To further complicate the evaluation of mycotoxins in livestock feeds, mycotoxin co-contamination of a single feed ingredient is more common than it is not. That is, if a feedstuff is contaminated by a single mycotoxin, it is likely that other mycotoxins are present as well. In fact, 72% of the North American feed ingredients included in the 2019 Biomin survey were contaminated by two or more mycotoxins. When multiple mycotoxins are simultaneously present in a feed ingredient, the interactive effects between mycotoxins can be described as additive, antagonistic, or synergistic. An additive interaction is one in which the combined effect of multiple mycotoxins is equal to the sum of the individual mycotoxin effects. If the combined effect of two or more mycotoxins is less than additive, the interaction is antagonistic, and if the combined effect is greater than additive, the interaction is synergistic. While it is essential to acknowledge the reality and complexity of mycotoxin co-contamination, implications of co-contamination are broad, encompassing many different mycotoxin combinations, and research in this area is still warranted.
Once cereal grains have been infected, there are very few processes that can effectively reduce the concentration or toxicity of mycotoxins. Thus, a strict plan for managing the presence of mycotoxins in feed manufacturing facilities should be established and dutifully followed to avoid introducing harmful amounts of toxic compounds to livestock. Not only is this a generally good management practice, it also can have regulatory implications. Since the adoption of the Preventative Controls for Animal Food rule in 2015, all animal feed manufacturing facilities are now required to have a Food Safety Plan outlining any potential hazards that may be inherent to the facility’s specific feed ingredients or manufacturing processes.
Subsequently, the facility must implement preventive controls to reduce the likelihood of such hazards contaminating animal feed. Per the Rule (FDA, 2015), mycotoxins are identified as potential chemical hazards posing a threat to animal health, and, if determined to be a legitimate risk, their presence must be monitored. Therefore, the following information may be useful in implementing preventive controls if mycotoxin contamination is a concern in your feed manufacturing facility.
The main objective of the mycotoxin management plan should be to identify points where mycotoxin contamination may occur and establish monitoring procedures at those points. Two primary areas of concern that will most likely be included in the plan are ingredient receiving and ingredient storage. The first step in reducing the threat of mycotoxins is to eliminate the possibility that contaminated feeds are introduced into the manufacturing facility. Two strategies to accomplish this are:
1) write clauses stating the maximum acceptable level of mycotoxins into the purchasing agreement for each ingredient suppler, and
2) develop a sample strategy for incoming bulk loads of grain and test for the presence of mycotoxins, specifically, aflatoxin, fumonisin, and DON. If a load tests greater than the regulatory threshold for a particular toxin or above the limits agreed to in the purchasing contract, it should be rejected and not unloaded. Although this can be labor intensive and time consuming, it is crucial for understanding the risk that is associated with different ingredients and ingredient suppliers.
At minimum, all bulk loads should be sampled until enough consecutive negative test results have been recorded that management feels the risk is under control. In addition, mycotoxin reports should be assessed to determine the risk of contamination. Frequency of sampling may then be reduced for ingredients or suppliers that have established the appropriate risk.
The key to effective sampling is to use the appropriate sampling tools and follow the proper sampling techniques to collect a sample that is representative of the entire bulk lot. This is especially important when analyzing mycotoxins as the concentration of mycotoxins throughout a single load are known to be highly variable.
The second step in reducing the threat of mycotoxin contamination is to maintain optimum grain storage conditions. Molds have five basic requirements for growth: oxygen, temperature, moisture, substrate, and time. Thus, grain storage bins can essentially serve as large mold incubators if storage conditions are not monitored properly. All grain storage bins will inherently have ample oxygen and substrate for mold growth. Therefore, temperature, moisture, and time become three primary factors affecting the quality of stored grain, given the initial quality of grains prior to storage is acceptable. It is generally recommended that storage conditions not exceed 14% moisture or 20°C to control mycotoxin contamination.
The toll of mycotoxins
It is estimated that mycotoxins cost the livestock industry an average of $6 million annually, according to the Council for Agricultural Science and Technology. Aside from losses associated with immediate death, the majority of poultry production losses may actually be incurred through the systemic, yet sometimes inconspicuous, reductions in growth rate, egg production, and immune system function that is experienced when mycotoxins are present in diets at concentrations below what is generally recognized as safe. Thus, it is necessary to understand the potential dangers associated with mycotoxin contamination, as well as steps that can be taken to reduce the probability of introducing mycotoxins into poultry feed.