Mycotoxicosis in Swine
Mycotoxins are toxic substances produced by molds and fungi on plants, in the field, or during storage.
The BIOMIN Mycotoxin Survey provides regular updates on the occurrence of mycotoxins in raw commodities and finished feed based on thousands of samples collected from across the globe in addition to regional reports on US corn-based feed ingredients.
Most affected raw materials pertinent to the swine industry are:
- Corn and corn by-products
- Small grains such as wheat and barley and small grain silages
- Soybean meal
- Plant oils
Mycotoxin contamination found in complete feed is often from multiple ingredients, regularly resulting in herd exposure to multiple mycotoxins over the course of their time in production.
Overall, mycotoxin risk management is critical to reduce the effects on animal health and performance, which when unaddressed, can lead to significant economic losses for producers.
General effects of mycotoxins on swine
The presentation of mycotoxicosis is a culmination of factors, including the nature of the mycotoxin exposure (duration, concentration, types of mycotoxins), the environment (management, hygiene, other pathogens, and stressors), and the status of the animal itself (species, life stage, sex).
Out of the livestock species, swine are considered the most sensitive, with poultry and ruminants being considered more resistant. Piglets and breeding stock are where mycotoxins can have the most significant impact on animal health and producer profitability.
Mycotoxins in general have drastic effects on the gastrointestinal tract, where the mycotoxins make direct contact to the gastrointestinal mucosa. Once mycotoxins are taken up into the blood stream, various internal organs and systems can be impacted. The liver, kidneys, and immune system can also be affected by several different toxins. Clinical presentations involving the respiratory system, nervous system, and integument can be observed depending on the mycotoxins present, while the reproductive system can be impacted through direct and indirect effects depending on degree of challenge. Overall mycotoxin exposure can culminate in decreased performance and increased sensitivity to pathogens.
These toxins are commonly found in areas where crops are subjected to heat and drought stress, and can be found in sub-optimal storage conditions. Aflatoxins can cause death when administered at high levels, but the greatest impact comes from reduced reproductive and performance capabilities. Aflatoxins suppress the immune system, cause hepatocellular damage and fatty liver syndrome in multiple species, and are highly carcinogenic. Aflatoxins can carry over into both meat and organ tissue.
Type A-Trichothecenes (A-Trich) consist of a group of multiple toxins, the best known of which are T-2 toxin and HT-2 toxin. Type A-Tricothecenes are considered more potent compared to Type B-Trichothecenes and are so potent that they can cause contact lesions in the oral mucosa. These toxins often contribute to reduced feed intake and poor performance, and often cause lesions throughout the gastrointestinal tract, as well as immune suppression.
Deoxynivalenol, acetyldeoxynivalenol, fusarenon X, and nivalenol, are all mycotoxins that are part of the Type B-Trichothecenes family. The most well-known is deoxynivalenol (DON), which is frequently referred to as “vomitoxin” for its ability to induce vomiting in swine.
DON inhibits intestinal nutrient absorption and alters intestinal cell and barrier functions. These mycotoxins significantly affect the immune system, reducing lymphocyte proliferation, macrophage activity, and antibody response to certain vaccinations and influence immunoglobulin levels.
Additionally, numerous studies have indicated that DON, by itself or in combination with other mycotoxins, may be a predisposing factor for disease.
Swine are one of the species most sensitive to fumonisins and can result in acute death due to porcine pulmonary edema (PPE). Although commonly thought to require high levels to impact animal health, chronic exposure can have profound impacts to gastrointestinal health, the immune system, and liver and lung function.
Low levels of fumonisins can increase the ability of E.coli to bind to enteric cells thus facilitating their crossing over into the blood stream. Chronic exposure to fumonisin B1 (FB1) decreases the proliferation of epithelial intestinal cells. Fumonisins are known to increase the risk and severity of respiratory disease in swine. Fumonisins also impair vaccination response through reducing the level of several specific antibodies and the period of vaccine protection. Fumonisins are an important consideration in mycotoxin risk management programs as they act as predisposing factors for diseases in multiple ways, and amplify the impacts of DON.
Despite relatively low levels of acute toxicity, zearalenone (ZEN) can have a significant impact on reproduction. Swine are among the most sensitive species to this mycotoxin, and even low levels of ZEN can affect reproductive performance.
Negative effects are due to the interaction of ZEN and its metabolites with estrogen receptors. In general, ZEN contaminated feed induces the swelling and reddening of the vulva, false heats, and false pregnancy. Higher levels can result in embryonic death, abortions, and stillbirths. Chronic ZEN exposure can result in atrophic ovaries and vaginal prolapse, as well as interfering with the reproductive development of replacement gilts.
Ergots can be formed by fungi growing on cereals or by endophyte fungi within tall fescue and other grasses. One of their main effects is vasoconstriction (restricting blood flow), which has an impact on hoof health, heat stress, mastitis, and reproduction.
Agalactia (due to interference with the release of prolactin), feed refusal, and consequent weight gain reductions are classical signs of ergot alkaloid intoxication. Other frequently noted symptoms have been observed in the cardiovascular and central nervous system because of increased blood pressure, causing vasoconstriction and strong uterotonic effects, resulting in stillbirths and reduced pregnancy rates.
Hepatotoxic effects, decreased performance parameters, nephrotoxicity, and necrosis are the major toxic effects caused by ochratoxin A. This mycotoxin has been shown to suppress cell-mediated immune response in pigs, resulting in reduced macrophage activity and weakened stimulation of lymphocytes. Furthermore, ochratoxin A tends to accumulate in kidneys, liver, and muscle tissues, as well as in blood serum and, therefore, it represents a potential hazard in the human food chain.
Synergistic effects of mycotoxins
Toxicological interactions between mycotoxins enhance the toxic effects, even at low levels.
Fusarium graminearum and Fusarium culmorum are known to produce several different fusariotoxins, including zearalenone and deoxynivalenol, which are known to interact synergistically. In addition, the analysis of deoxynivalenol often indicates the co-occurrence of other fusariotoxins such as other trichothecenes (T-2 toxin, nivalenol, diacetoxyscirpenol), zearalenone, and fumonisins.
Diagnosis of mycotoxicosis
Mycotoxicoses are diseases caused by ingestion of mycotoxins, inhalation, or contact with the skin. The effects of mycotoxins in livestock species are diverse, varying from immunosuppression to death in severe cases, depending on various factors including those which are toxin-related (type of mycotoxin consumed, level, and duration of intake), animal-related (animal species, sex, age, breed, general health, immune status, nutritional standing) and environmental (farm management, biosecurity, hygiene, temperature). This complexity often impedes correct attribution of problems caused by mycotoxins.
There are multiple diseases in swine that are attributed to stress stimuli and are opportunistic infections. Mycotoxins have been shown to be sufficient to induce and exacerbate multiple diseases, and thus preventative health programs for swine herds need to have a mycotoxin risk management plan in place.
Mycotoxin risk management
Robust mycotoxin risk management comprises three steps:
Reducing animal exposure to mycotoxins in feed is key. Regular analysis of feed components and complete feed can help to uncover potential threats to animals. Identifying contamination can help to reduce exposure and determine what the best options are for prevention and mitigation. However, a highly contaminated sample does not mean the entire crop is bad and a ‘clean’ sample does not guarantee that all of the feed is mycotoxin-free.
Good storage practices, along with proper bin and feeder management, are essential to avoid further growth of molds and thereby prevent the production of additional mycotoxins.
When it comes to counteracting mycotoxins, the livestock industry tends to think of toxin binders or mycotoxin binders first. (Learn the truth about mycotoxin binders). Regular application of mycotoxin binders is advisable; however, clay mineral binders are not an effective answer to all major mycotoxins. This is especially true when attempting to mitigate trichothecenes since their structures are not suitable for adsorbing by binders. Biotransformation, the use of microbes and enzymes to degrade mycotoxins, is the most effective strategy. This mode of action provides reliable protection against Fusarium mycotoxins by biodegrading mycotoxins into non-toxic metabolites.
In addition to biotransformation, a bioprotection strategy is also important. Feed additives containing plant and algae extracts provide support to the liver and the immune system.
A combination of different strategies can counteract the negative effects of mycotoxins, especially in cases of multi-mycotoxin contamination with the poorly absorbed Fusarium mycotoxins in swine feed.
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