Mycotoxicosis in swine: which are the most important ones?
Mycotoxicosis is a major problem in swine production due to its presence in feed and pathogenic effects on the farm.
Mycotoxicosis is a major problem in swine production due to its presence in feed and pathogenic effects on the farm.
What are mycotoxins and what is their impact?
There are many fungal species that produce toxic metabolites called mycotoxins. These microorganisms often contaminate animal feed as they grow on forages or stored feed when conditions are favorable.
The environment is a key factor in the development of mycotoxins since certain environmental parameters such as temperature and humidity are related to these metabolites. Fungi grow under certain conditions that allow them to produce metabolites that contaminate feed and have a great impact on swine health.
It has been estimated that in the United States the problem of mycotoxicosis in swine causes losses of USD 147 million each year. The mycotoxins involved in these losses can be aflatoxin, fumonisin and vomitoxin (DON). In addition, it is estimated that more than 20% of feed and swine feedstuffs are contaminated with fungi producing these mycotoxins. The global contamination of crops with mycotoxins is close to generating losses of USD 1.6 billion each year.
These mycotoxins are strictly regulated in each country due to their importance in animal and public health. For this purpose, analyses of animal products and food supplies are carried out to determine the mycotoxin load and ensure food safety.
How do mycotoxins originate?
Most mycotoxicosis problems in swine are associated with contaminated grains used for feed manufacture, such as corn, wheat, barley, among others.
Fungi associated with mycotoxicosis require ideal conditions for their development. Therefore, fodder and feed are a good source of carbohydrates required by the microorganisms for their metabolism, an adequate amount of oxygen and temperatures in the range of 12-25°C. In addition, crops affected by disease are more likely to suffer from fungal contamination. These stressors for forages can be extreme droughts, high temperatures, damage by insects or physical means, diseases caused by microorganisms, among others. However, it should be noted that the level of fungal contamination is not fully significant in predicting the number of mycotoxins present in a feed.
Fusarium species of fungi are characterized by growth in raw material crops with humidity conditions higher than 70% and mold growth. On the other hand, Aspergillus spp. and Penicillium spp. grow in stored foods with temperatures between 10-50°C.
Mycotoxin production occurs in all crops worldwide, however, its prevalence changes according to the geographical region involved and its environmental conditions. There are conditions that favor the growth of these mycotoxins such as crop damage, transport, sudden temperature changes, improper storage, among others. Some of these mycotoxins and related factors are summarized in Table 1.
Mycotoxicosis in swine: What is it?
Mycotoxicosis is defined as an intoxication by consumption of a high number of mycotoxins by an animal. This quantity is usually measured in parts per million (ppm) of mycotoxins consumed which have a wide variety of clinical signs and effects at the productive level. These consequences are related to the immune and health status of the animals involved.
The probability of mycotoxicosis in swine increases if the animals have a diet deficient in protein, vitamins, and minerals. In addition, animals can be affected by mycotoxicosis due to one or more mycotoxins acting together at the same time with a synergistic effect.
Some of these mycotoxins have been reported to have an immunosuppressive effect that predisposes swine to the development of other diseases.
There are six groups of mycotoxins recognized as having the greatest impact on the swine industry because of their effects on affected farms: aflatoxins, ochratoxins, DON, Zearalenone, Fumonisins, ergot alkaloids.
Aflatoxicosis in pigs
Aflatoxins (AF) are produced by fungi of the genus Aspergillus, the most important species being A. flavus, A. parasiticus and A. nomius, which are mainly found in stored feeds. These toxic metabolites are classified into AFB1, AFB2, AFG1 and AFG2. Of these, AFB1 produced by A. flavus is the most important because of its persistence in feeds that were damaged by insects or drought.
In swine, AFB1 is metabolized in the liver and produces seven toxic secondary metabolites, which bind to DNA, RNA, and proteins, causing damage at the cellular level. This affects hepatic lipid metabolism and protein synthesis, which severely affects swine health and production.
The toxicity of aflatoxins is 20 ppm in the daily diet for acute intoxication, and 2-4ppm of mycotoxins consumed daily for prolonged time where chronic lesions are seen that can be fatal. Intoxications with 270 ppb cause a long-term decrease in production efficiency by reducing feed intake in pigs and causing weight loss.
In piglets exposed to AFB1 a decrease in body weight was observed. Liver lesions were observed in animals over 65 kg.
Clinical signs observed in pigs with aflatoxicosis are depression, anorexia, anemia, ascites, coagulopathies. Liver enzymes may be elevated, as well as coagulation tests. These signs are caused by hepatic hemorrhages and fatty degeneration and hepatic necrosis. In addition, a potent immunosuppressive effect has been observed that triggers cases of swine erysipelas, dysentery, and salmonellosis.
Ochratoxin A in pigs
Ochratoxin A (OTA) is one of the most important mycotoxins in swine and is recognized for its pathogenic effect on the kidney. In this organ, this mycotoxin blocks the function of enzymes and ATP and promotes lipid peroxidation. In addition, it causes lesions of the genetic material at the cellular level which affects the function of multiple organs and causes immunosuppression.
In swine, OTA is considered lethal at doses of 1mg/kg of live weight for 5 to 6 days. At doses of 1 ppm for three months, it has been observed that animals show polydipsia, polyuria, and growth retardation. Doses of even 200ppm cause renal lesions.
Ochratoxin A in swine causes necrosis of renal cells at the level of the proximal contour tubules, altering the electrolyte balance in pigs. In addition, there is damage at the hepatic level by fatty changes and necrosis.
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Trichothecenes: T2 and DON
Trichothecenes are a broad group of mycotoxins produced mainly by the fungus Fusarium graminearum. In this group are classified mycotoxins of great importance such as T2, DAS and vomitoxin (DON).
The effects of T2 in swine are related to dermal and gastrointestinal lesions. In more severe cases, animals show cardiac failure, shock, and sudden death. Pathogenic effects can be observed even at minimal doses and DON is known to decrease feed intake in swine by as much as 1 to 10 ppm. This decrease in the amount of feed intake is produced by a series of enzymatic and hormonal reactions that are triggered by the consumption of DON in the feed. Thus, pigs enter periods of anorexia.
Zearalenone affects reproduction in sows
There is a fungus called Fusarium graminearum that produces Zearalenone, a mycotoxin with significative impact on the reproductive system of sows. This fungus grows in an environment of high humidity (23-25%) and sudden temperature changes.
Zearalenone is absorbed at the intestinal level and acts as a resorcicyclic acid lactone, generating a competition with the estrogenic hormone in cell receptors. In this mycotoxicosis, the metabolite binds to estrogen receptors in the uterus, mammary gland, liver, and hypothalamus of sows. Upon metabolization in the liver, alpha estradiol is produced which has even greater estrogenic activity, interfering with the physiological cycles of the endocrine and reproductive systems of sows.
At low doses of 1-5 ppm in sows, vulvogaginitis, vulvar edema and premature mammary development, as well as tenesmus and rectal prolapse have been found to occur. At higher doses, sows may have ovarian follicle atresia, delayed sexual maturity, prolonged periods of anestrus and reduced body weight. In addition, this mycotoxin is secreted in milk and may affect the development of lactating piglets.
Ergotism in swine
Ergot alkaloids are a group of mycotoxins produced by fungi of the species Claviceps purpurea affecting rye and wheat. This fungus invades plants and produces toxic metabolites of the alkaloid type (ergotamine, ergosine, etc).
The mycotoxicosis produced by these alkaloids is called ergotism and is characterized by gangrene and affects the reproductive system of sows. Gangrene is a product of vasoconstriction and endothelial damage produced in the blood vessels. Other signs observed in pigs include depression, reduced feed intake, tachycardia, and tachypnea. In addition, swine may suffer laminitis due to deficits in blood supply to the hoof.
At the reproductive level, ergotism generates agalactia in sows due to blockage of prolactin receptors. This affects lactating sows and growing piglets.
Fumonisins: What do they generate in swine?
Fusarium moniliforme and Fusarium proliferatum are two species of fungi that cause fumonisin mycotoxicosis, especially in corn forages. Pigs that consume these mycotoxins suffer from porcine pulmonary edema PPE (Porcine pulmonary edema PPE). The most common fumonisins are classified as B1, B2 and B3. They develop in forages with high humidity environments and are heat resistant.
Fumonisins affect cell functions and cycles by inhibiting the sphingosine converting enzyme. This interferes with cell signaling and protein formation pathways, as well as inducing cell death.
In pigs, pulmonary edema and hydrothorax are observed in 50% of the population affected by fumonisins. In addition, these sick animals have a high mortality of over 50% with signs of weakness, depression, salivation, dyspnea, tachypnea, decubitus, and death. Finally, this mycotoxicosis is considered to have an immunosuppressive effect in pigs.
How are mycotoxicoses in swine diagnosed and prevented?
The diagnosis of mycotoxins is complex due to the molecular nature of these metabolites and the scarcity of diagnostic tests focused on them. Therefore, the diagnosis of mycotoxicosis in swine is oriented to the observation of clinical signs of each type of mycotoxin and the clinical history of the farm.
There are mycotoxin analyses in forages and stored feed, but their high cost prevents them from being common tests for production. However, there is the possibility of guiding the diagnosis from paraclinical tests such as blood samples to analyze blood parameters, cell count, enzyme measurement and morphological changes at the cellular level. These tests allow a more accurate identification of lesions caused by mycotoxins in swine.
On the other hand, the prevention of this problem in swine production focuses on environmental management and the use of mycotoxin binders that allow blocking the effect of these metabolites in the animal’s organism, preventing the onset of lesions.
Environmental control focuses on crop level by taking measures against forage damage caused by insects, physical damage, and prolonged drought. Thus, it is recommended to protect crops with means to reduce the insect load and ensure sufficient irrigation for plantations. In addition, it is urged to improve storage, transport, and processing conditions of raw materials to avoid contamination by fungi.
Besides, mycotoxin binders are an excellent tool to reduce the load of toxic metabolites in the feed to be provided to pigs. Alquerfeed Antitox is a mycotoxin binder composed of Silicoglycidol which is an efficient molecule patented by Biovet S.A. This molecule is specialized in capturing these toxic metabolites without interfering in the absorption of nutrients in the digestive tract of pigs. In this way, the product prevents the damage caused by mycotoxins in a preventive way.
Mycotoxicoses are a persistent problem of great importance in the swine industry today. These molecules are toxic metabolites produced by fungi that contaminate forages and feed.
There are several conditions and factors that favor the growth of fungi and their production of mycotoxins that vary according to production systems and geographical location. Mycotoxicoses are a problem that affects pigs at a productive level, as well as causing lesions in the reproductive, digestive, and respiratory systems.
There are groups of mycotoxicoses of great importance in swine farming because they are mostly present in the cases reported at present. These groups are aflatoxicosis, ochratoxicosis, trichothecenes, zearalenone, ergotism and fumonisins. These mycotoxins are responsible for causing lesions in various organs and systems in pigs, significantly affecting swine production.
Finally, the diagnosis of mycotoxicosis requires specialized analysis to find the causal metabolite and its amount. This diagnosis should be complemented by clinical history, blood, and urine analysis (enzymes, proteins). Likewise, treatments are focused on prevention and reduction of mycotoxin load in feed with the use of mycotoxin binders and environmental management.
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