Mycotoxin is a toxin produced by an organism of the fungus kingdom, which includes mushrooms, molds and yeasts. Most fungi are aerobic (use oxygen). Fungi are found almost everywhere in extremely small quantities because of their spores, and are most commonly microscopically small. They consume organic matter, wherever humidity and temperature are sufficient. Mycotoxins are secondary metabolites produced by certain species of fungi growing under specific environmental conditions.
Primary metabolites are those produced by all fungi for both the synthesis of biomass and to generate the energy necessary for primary metabolism. In contrast, secondary metabolism is usually restricted to a small number of species and it occurs mainly after a phase of balanced growth, usually associated with morphogenetic changes like sporulation.
Secondary metabolites include pigments and compounds active against microorganisms (antibiotics), plants (phytotoxins) or animals/humans (Mycotoxins). The biological role of secondary metabolism in fungi is still unknown. The environmental factors that determine fungal growth and Mycotoxin production in feeds and feedstuffs are related both to the substrate itself (intrinsic factors) and to the storage conditions of the substrate (extrinsic factors). Mycotoxins are toxins produced by molds (fungi) that, when they are ingested, can cause diseases called mycotoxicosis.
These diseases are are not infectious. The effects on the animal are caused by fungal toxins in foods ingested, usually grains, and are not caused by infection with the fungus. Many different molds produce mycotoxins and many corresponding disease syndromes have been described for domestic animals.
Common Members of the Mycotoxin Family
Aflatoxins are produced by Aspergillus species, and are largely associated with commodities produced in the tropics and subtropics, such as groundnuts, other edible nuts, figs, spices and maize. Aflatoxin B1, the most toxic, is a potent carcinogen and has been associated with liver cancer.
Ochratoxin A is produced by Penicillium verrucosum, which is generally associated with temperate climates, and Aspergillus species which grow in warm humid conditions. Aspergillus ochraceus is found as a contaminant of a wide range of commodities including cereals and their products, fruit and a wide range of beverages and spices. Aspergillus carbonarius is the other main species associated in warm humid conditions found mainly on vine fruit and dried vine products particularly in the Mediterranean basin. It causes kidney damage in humans and is a potential carcinogen.
Patulin is associated with a range of fungal species and is found in moldy fruits, vegetables, cereals and other foods. It is destroyed by alcoholic fermentation and so is not found in alcoholic drinks. It may be carcinogenic and is reported to damage the immune system and nervous systems in animals.
Fusarium toxins are produced by several species of the genus Fusarium which infect the grain of developing cereals such as wheat and maize. They include a range of mycotoxins including the fumonisins, which affect the nervous systems of horses and cause cancer in rodents; and the trichothecenes, including deoxynivalenol, and zearalenone, the last two of which are very stable and can survive cooking. The trichothecenes are acutely toxic to humans, causing sickness and diarrhea and potentially death.
Effects of Mold
- Moldy feeds are less palatable and may reduce dry matter intake. This in turn leads to a reduction of nutrient intake, reducing weight gains or milk production. Performance losses of 5 – 10% are typical with moldy feeds even in the absence of mycotoxins. Mycotoxin contamination increases production losses, even when mold is not readily visible.
- Moldy feed may have reduced digestibility and energy content may need to be adjusted down by 5%. Molds grow and propagate deriving energy from the feed’s protein, fat and carbohydrate. Dietary fat in particular is reduced in mold infected feeds. Suggested that book values for energy be multiplied by 0.95 in the presence of substantial amounts of mold (ie 95% of energy value). Some researchers suggest reducing energy by as much as 10% (ie 90% of energy value).
- Moldy feeds may cause health problems. Feeding moldy feeds increased problems with mycotic abortions and respiratory disease. Feeding cattle moldy feeds is also hazardous to human health – farmers lung may result from breathing in mold spores.
Moldy Feed and Mycotoxins
- Mold spore counts may underestimate the amount of mold present and be a poor indicator of the potential risk.
- Moldy or musty feed will not always contain harmful mycotoxins. Moldy feeds may contain mycotoxins but not at harmful levels.
- Molds may produce harmful levels of potent mycotoxins under certain circumstances. Molds may always produce some mycotoxins.
Effects of Mycotoxins
- Initially mycotoxins cause relatively minor problems. The reduction in performance may be negligible. Within days or weeks, the effects of continued mycotoxin consumption on performance (milk production or weight gains) becomes more pronounced.
- Off-feed, ketosis and displaced abomasum problems may increase significantly with the consumptions of mycotoxins. Some animals develop diarrhoea or have signs of haemorrhaging.
- Estrogenic effects, swollen vulvas and nipples; vaginal or rectal prolapse may occur. Reduced fertility / conception rates or abortions may also be evidence of mycotoxin consumption.
- The effects of mycotoxins are amplified by production stress. High producing dairy cows and rapidly growing feedlot cattle are more susceptible to the effects of mycotoxins than low producing animals.
Losses Due to Mycotoxins
Losses from mycotoxins are associated with regulatory losses, as opposed to lowered production, illness, and/or deaths from the effects of the toxins. This is particularly the case for human food, but increasingly it has become the case for animal feeds, as strict feed quality control programs become the norm for large-scale animal production units. Aflatoxin are proven carcinogens, immunotoxins, and cause growth retardation in animals. Fusarium toxins, specifically fumonisins, are reported carcinogens and trichothecenes are reported immunotoxins.
Mycotoxin management costs are incurred by both producers and the Federal and state governments to prevent mycotoxins from becoming a human and animal health threat. The Food and Drug Administration (FDA) has functioning mycotoxin regulatory programs for aflatoxin, fumonisins, and vomitoxin.
Aflatoxin is the mycotoxin generating the greatest losses and the highest management costs due to its extremely high toxicity on a unit basis, and its long history of stringent regulation. The peanut, corn, cottonseed, and tree nut industries all recognize losses associated with meeting regulatory levels. The costs are inversely related to the regulatory level that must be met, and lower concentration allowances will increase the costs of crop management.
Suggestions to Prevent Mycotoxin Contamination of Feed Stuffs
- Control the environmental factors that influence fungal growth: (Diekman and Green, 1992)
- Moisture content of grain (<14%)
- Relative humidity (<70%)
- Temperature (-2.2 Centigrade)
- Oxygen availability (<0.5%)
- Minimize grain damage during harvest
- Screen grain to reduce broken kernels
Animal aspects: (Adapted from Dr. Thompson’s lecture)
- Reduce the stress to animals
- Increase plan of nutrition
Muhammad Nauman Manzoor
M.Sc. (Hons) Animal Nutrition