Mycotoxins are secondary metabolites produced by a wide variety of filamentous fungi, including species from the genera Aspergillus, Fusarium and Penicillium. The fungi typically grow on various feedstuffs, such as grains and cereals. Mycotoxins are invisible, tasteless, chemically stable, and survive high temperatures and many environmental conditions. Most animal feedstuffs are likely to be contaminated with multiple mycotoxins. The growth of moulds and mycotoxin production occurs worldwide, especially in climates with high temperatures and humidity and where grain is harvested with high water content. The Food and Agriculture Organization (FAO) estimates that as much as 25% of the world’s agricultural commodities are contaminated with mycotoxins, leading to significant economic losses.
The most common source of food and feed contamination are mycotoxins produced by the fungi Aspergillus, Penicillium and Fusarium genera. Other mycotoxin-producing fungi include Alternaria, Chaetomium, Cladosporium, Claviceps, Diplodia, Myrothecium, Monascus, Phoma, Phomopsis, Pithomyces, Trichoderma and Stachybotrys.
While Aspergillus and Penicillium species are generally found as contaminants in feed during storage, Fusarium and Alternaria species can produce mycotoxins before harvesting or immediately after. Every plant can be contaminated by more than one fungus, and each fungus can produce more than one mycotoxin. Up until now, approximately 400 secondary metabolites with toxigenic potential produced by more than 100 moulds have been reported.
Aspergillus, Fusarium, Penicillium and Claviceps produce the most extensively studied mycotoxins. Some of the mycotoxins produced by these moulds include aflatoxins, ochratoxins, deoxynivalenol (DON), T-2 toxins, zearalenone, fumonisins, Citrinin and ergot alkaloids. Mycotoxins cause diverse effects on animals, such as carcinogenesis, hepatotoxicity, and neurotoxicity, as well as impaired reproduction, digestive disorders, immunomodulation, and decreased performance.
Multiple factors determine the contamination of agricultural commodities with mycotoxins. Mycotoxin occurrence varies between crops, as fungal species and strains differ in their ability to infest a particular host. It also varies between varieties of the same plant species, as varieties show different levels of susceptibility or resistance to fungal infestation. Furthermore, environmental conditions, such as temperature and humidity, affect the infestation of crop plants with mycotoxigenic fungi and mycotoxin; therefore, climate and weather are strong determinants of mycotoxin contamination. Moreover, agricultural practices, the timing of harvest, and post-harvest handling of crops affect mycotoxin formation.
Crops may be infested with multiple strains of fungi, and most fungal strains produce more than one type of mycotoxin. Therefore, co-contamination of agricultural commodities with multiple mycotoxins is frequently observed. When feed raw materials are mixed, mycotoxin co-contamination becomes even more likely. If mycotoxins co-occur, their combined toxic effect may be much greater than the summed effects of the individual mycotoxins.
The presence of mycotoxins in poultry feed is a significant challenge causing health and performance issues, as well as substantial financial losses. Poultry are susceptible to a wide range of mycotoxins including aflatoxins, ochratoxin, fumonisins, zearalenone, trichothecenes such as deoxynivalenol, and T-2 toxin.
Aspergillus flavus and Aspergillus parasiticus produce aflatoxins, which are found in feed ingredients used for poultry. Aflatoxins in poultry are responsible for weight loss, low feed efficiency, reduced egg production and egg weight, enhanced liver fat, alteration in organ weights, decreased serum protein levels, carcass bruising, poor pigmentation, liver damage, low digestibility of starch, protein, and lipids, immunosuppression, disease outbreaks, and vaccination failures.
Ochratoxins are produced by Aspergillus and Penicillium. Ochratoxin-contaminated diets increase the weight and size of the liver and kidneys but reduce the weight and size of lymphoid glands, such as the thymus, bursa of fabricius, and spleen in broilers. In addition, ochratoxin causes lesions in the kidneys, liver, bursa of fabricius, spleen, and thymus. Ochratoxin can reduce production performance, and results in blood biochemical disturbances and severe immunosuppression in broilers and layer hens.
Fumonisins are produced by Fusarium verticillioides cultures. Fumonisins reduce body weight gain, decrease feed intake, and cause liver damage in chickens, ducks, and turkeys. In chickens, liver alteration includes multifocal liver necrosis and biliary expansion. In turkeys and ducklings, the observed liver changes include diffuse enlargement of liver cells with biliary expansion.
Fusarium graminearum and Fusarium roseum are sources of zearalenone, which is a mycotoxin with estrogenic activity. Zearalenone occurs in corn, sorghum, wheat, barley, oats, milo, rye, and other grains. Zearalenone has potential adverse effects on bird performance and egg yield and may be an indicator of other potentially toxins present in feed. Zearalenone mycotoxicosis in broiler affects the reproductive tract and sex hormone-sensitive receptors. In poultry layers and breeders, it impacts egg specific gravity, eggshell thickness, interior egg quality, decrease in serum calcium and increase of phosphorus content, reduced feed intake and egg production, inflammation of the bursa of fabricius, hormone-induced cloacal swelling, cysts developed on the peritoneal surface and within the oviduct decreased comb and testes weight, oviduct enlargement and leukopenia (decrease in the number of White Blood Cells).
Trichothecene mycotoxins are the most potent small-molecule inhibitors of protein synthesis, including T2 toxin, deoxynivalenol (DON) or vomitoxin, Nivalenol, HT2 toxin and diacetoxyscirpenol (DAS). Trichothecene causes oral lesions, reduction in growth performance, abnormal feathering, reduced egg development and eggshell consistency, regression of the bursa of Fabricius, peroxidative changes in the liver, abnormal blood coagulation, leucopoenia and proteinemia, and immunosuppression. T2 toxin reduces the relative weights of the bursa of fabricius, thymus, and spleen, and causes a swollen liver, friable, and yellowish discoloration in the gall bladder, mild haemorrhage and inflammation in the heart, erosion in the trachea, and inflammation of the air sacs in broilers. Deoxynivalenol alters the main gut functions, decreases the villus surface area available for absorption, and affects gut permeability.
Contamination of feed commodities with fungus is commonly seen in every part of the world and it varies from region to region depending upon the environmental conditions like temperature and humidity. Prominent mycotoxins occurring in agricultural commodities, include: aflatoxins (AFLA), ochratoxin A (OTA), zearalenone (ZEN), deoxynivalenol (DON), fumonisins (FUM) and T-toxin (T-2). Some of these mycotoxins have hepatotoxic, nephrotoxic, immunosuppressive, genotoxic, teratogenic, and/or carcinogenic effects in animals. During the last 10 years, incidence of multiple mycotoxins (AFLA, OTA, ZEN, DON and FUM) produced by different fungal species particularly Fusarium and Aspergillus genus have been reported in cereals from different countries. Co-occurrence now gains much attention worldwide owing to its more toxic capacity (synergistic effect) as compared to single mycotoxin. According to studies, more than 50% of mycotoxin contaminated feed samples contained multiple mycotoxins. The co-occurrence of mycotoxins can affect both the production of mycotoxin and the toxicity of the contaminated material. Frequency of mycotoxins produced by Fusarium fungal species containing DON, FUM, ZEN are more frequent and co-occurrence of these mycotoxins can result severe detrimental impacts. The majority of mycotoxins in animal feed are associated with lower performance, poor growth, health and reproductive issues and significant economic impact on livestock production.
Existence of mycotoxins in poultry feeds aggravates coccidiosis in poultry; even its small amount can increase Eimeria infection and disease sternness in Poultry. Factors responsible for mycotoxins’ intensification of coccidiosis include mycotoxin contamination in feed, higher immunosuppressive effects on broilers, and the possible synergistic effects between mycotoxins.
Mycotoxins in feed reach the gastrointestinal tract of animals which is the most affected organ by them. Animal productivity depends heavily on the ability of the gastrointestinal tract to convert feed into energy. Additionally, the gastrointestinal tract is the largest immune organ in the body. Mycotoxins Impact intestinal morphology by increasing villus fusion and decreasing tight junction formation. These effects lead to a ‘leaky gut’ condition which increases the proliferation of secondary pathogens such as Clostridium perfringens, E. coli, Salmonella, and Coccidia. In addition, mycotoxins interfere with the absorption of nutrients from the intestinal surface, which is why mycotoxins are closely associated with some significant poultry diseases.