Definition and Types of Mycotoxins
Dr. Fausto Solís, Nutrition Services Manager
The term “mycotoxin” is derived from “mykes” meaning fungi and “toxicon” meaning poison. Mycotoxins are toxic metabolites of fungi commonly found in cereal grains. There are over 200 species of molds that produce mycotoxins; however, six are the most important that can affect the health and productivity of animal species. Those mycotoxins that can produce a variety of diseases in poultry and swine are Aflatoxins, Ochratoxin, Deoxynivalenol (DON), T-2, Zearalenone, and Fumonisins.
Aflatoxin is a potent mutagen and hepato-carcinogenic mycotoxin produced by the fungus Aspergillus flavus and Aspergillus parasitius that affects a wide range of animal species. Chronic exposure to aflatoxin may significantly alter productivity in animals and impose a risk to the consumers from direct exposure to contaminated food commodities. Since the liver is the target organ of aflatoxin in broilers, the contamination with aflatoxin is characterized by a severe hepatic enlargement and fatty infiltration. In poultry, aflatoxin inhibits weight gain, reduces feed efficiency, reduces egg production and egg weight; it may also increase fat in the liver, carcass bruising, poor pigmentation, and liver damage. The performance of the animal is reduced because aflatoxin decreases activities of several enzymes involved in the digestion of starch, protein, lipids, and nucleic acids, and causes immunosuppression. The immunosuppressing effect of aflatoxin may contribute to the outbreaks of many diseases and failures of vaccination.
Even though swine species are less susceptible to aflatoxin than poultry, the maximum level allowed in feed and ingredients by the Food and Drug Administration (FDA) is 20 ppb.
Ochratoxins are mycotoxins produced by the fungi Aspergillus and Penicillium. Signs of ochratoxin toxicity in poultry include weakness, anemia, decreased feed consumption, reduced growth rate and egg production, poor feathering, and excessive mortality at high dietary concentrations. Increases in the relative weights of liver, spleen, pancreas, proventriculus, gizzard, and testes in poultry are also observed in ochratoxin toxicity. Ochratoxins interfere with the synthesis of DNA, RNA, and protein and carbohydrate metabolism. Ochratoxin may also cause loss of pigmentation because it reduces the synthesis of carotenoids in broilers; this effect is more severe than that caused by aflatoxin. The most characteristic effect of an ochratoxin toxicity is the hypertrophy, inflammation, and malfunction of kidneys in both poultry and swine.
DON and T-2
DON (vomitoxin) and T-2 belong to the group of mycotoxins called trichothecenes, which are the most potent inhibitors of protein synthesis followed by a secondary disruption of DNA and RNA synthesis. Toxic effects of this group of mycotoxins include oral lesions, growth retardation, abnormal feathering, decreased egg production and eggshell quality, regression of the bursa of Fabricius, changes in liver, abnormal blood coagulation, and immunosuppression. Concentrations of T-2 that cause oral lesions are lower (0.4 ppm) than concentrations that decrease chick performance (3–4 ppm) whereas ducks are affected when the dietary concentration is as low as 0.4 ppm.
The level of DON that affects chick performance is still debated; some researchers report toxic effects at 16 ppm, whereas others report no toxic effect until dietary concentrations exceeded 116 ppm of DON.
On the other hand, pigs are the most susceptible species to DON. In several studies, it has been demonstrated that DON at concentrations ranging from 1 to 7 ppm significantly alters several key functions of the intestinal tract including decreasing villus surface area available for absorption and altering the permeability of the intestinal tract.
DON level above 1.5 ppm of feed in pigs primarily decrease feed intake, immune suppression, and, at higher concentrations, a complete feed refusal might be observed in this type of animal. In addition, higher levels of DON fed to pigs have shown to reduce average daily gain (ADG) and reduce feed efficiency.
Zearalenone is a mycotoxin produced by the fungi Fusarium graminearum and Fusarium culmorum in cereals, which have estrogenic and anabolic actions in the reproductive tract. Zearalenone has hematotoxic (blood toxicity), hepatotoxic (liver toxicity), and immunotoxicological effects (immune system) as well as carcinogenic, mutagenic, and genotoxic activity. It appears that zearalenone does not have important effects in poultry species; however, it has been shown that there is breed specific susceptibility to mycotoxins, and, in some species of poultry, an increase of the bursa of Fabrisius with 30 ppm of zearalenone has been observed; in general, turkeys have shown to be less resistant to zearalenone than chickens.
The main symptoms described in swine are anestrous and reduced litter size, edema of the vagina, mammary gland enlargement, swelling and reddening of the vulva in gilts. In several studies, zearalenone has shown to increase the size of the uterus and ovary weights in pigs, which prove the estrogenic effect of zearalenone on the reproductive system of pigs. Zearalenone acts on the secretion of the Follicle Stimulant Hormone (FSH), which depresses the maturation of ovarian follicles during the pre-ovulatory stage. Greater levels of FSH in gilts has been observed with 2 ppm of zearalenone. Higher levels of zearalenone (3.2 ppm) increased the size of the liver and kidneys in swine.
Fumonisins are mycotoxins produced by the fungus Fusarium. Although the most susceptible animals to fumonisins are horses and swine, mild to moderate toxicity has been reported in chicks, ducks, and turkeys fed rations containing 75–400 ppm. It has been reported that in diets with more than 150 ppm, liver pathology such as hyperplasia might be observed in ducklings and turkeys. It has been demonstrated that feed intake is reduced in turkeys fed 50 ppm, which suggests that turkeys are more susceptible than chickens to fumonisins.
Swine are very susceptible to fumonisins with the porcine pulmonary edema, which causes very serious pneumonia and respiratory distress as the most pronounced diseases in diets containing 10 ppm of fumonisins; at this level of contamination, decreased ADG and feed efficiency in post-weaned piglets has been observed.
Interactions among Mycotoxins and Mycotoxin Prevalence
In general, contaminated feeds usually contain more than one mycotoxin. Most of the studies showed a synergistic or additive interaction of mycotoxin on animal performance. Combination of mycotoxins, at concentrations that individually should not cause negative effects, may negatively affect animals.
In a survey done by Biomin in 2016, it was observed that 83% of the corn has at least one of the six more common mycotoxins and 58% of the samples are contaminated with multiple mycotoxins (≥2 mycotoxins). According to a 3-yr global survey, the most prevalent (65% of finished feed) mycotoxin in North American feedstuffs is deoxynivalenol (DON) known for its feed intake suppression and immunomodulatory effects in pigs when present in diets at or over 1 ppm.
Factors affecting Mycotoxin Incidence and Managing Mycotoxins
Some environmental factors such as high temperature, low rainfall, high moisture levels, and insect infestation may make the grain prone to mycotoxin contamination.
The prevention of mycotoxins should begin by preventing and controlling the fungi producing the mycotoxins. Fungi survive and grow in dark and humid environments; so, lowering the moisture content of plant seeds after harvesting and storage is one of the major steps to prevent mycotoxins. Additionally, high temperatures are favorable for the proliferation of fungi and their metabolites (mycotoxins); therefore, it is advisable to store commodities at low temperature whenever possible. Some chemical compounds such as fungicides and preservatives have shown to be effective against fungus development. A routine insect control program helps to prevent insect infestation in stored bulk. After the grains have been infected, a common way to prevent mycotoxin diseases in animals is to use adsorbent compounds such as detoxifying agents based on aluminosilicate (clays), yeasts, diatomaceous earth, and enzymes. There are some studies showing that these compounds may bind mycotoxin molecules and prevent contamination by taking them out of the organism. In other studies, it has been shown that hydrothermal treatments, including pelleting, may reduce the mycotoxin population and alleviate mycotoxin effects.
Mycotoxins can be a complicated and technical subject, but Wenger Feeds monitors toxin levels throughout the year and makes adjustments to our proprietary diets as needed. Please talk to your account leader for more information.