Mycotoxins are unavoidable contaminants in foods and feeds and are a major problem all over the world.Mycotoxicoses underlines simplicity of the source and the complexity of the problem All mycotoxins are low-molecular-weight natural products produced as secondary metabolites by filamentous fungi. Most fungal toxins occur in families of chemically related metabolites: over 300 to 400 compounds are now recognized as mycotoxins, of which nearly a dozen groups regularly receive attention as threats to human and animal health. The major toxins of poultry importance include Aflatoxin, Ochratoxin,Citrinin, oosporin, T2 toxin etc.
Mycotoxins cause a wide range of toxic responses ranging from mortality to subtle effect like immunosuppression and biochemical alterations. Acute outbreaks are rare events in modern poultry production. However, low levels of mycotoxin contamination, which very often are not detected, are responsible for reduced efficiency of production and increased susceptibility to infectious disease. Low levels of several toxins in feed is more dangerous as most of them work synergistically
Varying sensitivities are noticed to the mycotoxins, depending on species, sex, breed, strain, physiology, age, nutrition, other diseases, presence of other environmental factors and management.
The fungi producing the mycotoxins have simple requirements for existence and flourishing. They simply need a source of carbon and nitrogen; they do require water; all they need oxygen, although some require much less than other. In general hot and humid condition are favorable. Most of feed stuffs will provide suitable substrate both pre and post-harvest.
Most fungi are able to produce several mycotoxins simultaneously Some of fungal spp have capabilities to produce more than one mycotoxins as well single toxin is produced by multiple sp. The mycotoxins produced depends on the feedstuff and crop growing conditions and this has been demonstrated in worldwide mycotoxin surveys
With massive fluctuations in climate the quality level of raw materials and feeds for our animals’ consumption and the mycotoxin challenge can be severe, especially in subtropical environments Stress factors such as drought, high crop densities, insect damage can promote the development of fungus and subsequent mycotoxin production. In a future where climate change may significantly affect the worldwide distribution and contamination by mycotoxigenic fungi and mycotoxins , the analysis of levels of contamination as well as the implementation of prevention and control strategies will be of major concern
As it is a common practice to use multiple grain sources in animal diets, the risk of exposure to several mycotoxins increases with diet complexity. Some unidentified fungal metabolites that may contribute to an underestimation of the total amount of mycotoxins. Moreover, the nutritive value of grains may be lower due to fungi invasion, and thereby may cause a greater effect on animal productivity
We need to understand that the demonstration of fungal contamination is not the same thing as the demonstration of mycotoxin contamination. Because fungi might have died but producing toxin. Grains presently looking dry would have had toxins. inaccurate test result from sampling leading to underestimation of mycotoxin risk assessment for preventative action. As per the survey.Two-thirds of samples contained two or more
Mycotoxins are hard to define:
Mycotoxins are not only hard to define, they are also challenging to classify due to their diverse chemical structures and their production by a wide number of different fungal species . mycotoxins can be classified as hepatotoxins, nephrotoxins, neurotoxins, immunotoxins., the demonstration of mold contamination is not the same thing as the demonstration of mycotoxin contamination. In most cases, these subclinical conditions of mycotoxins level always impair multisystemic of the animals especially impaired immune function leading the animals to develop secondary infections along with failure of vaccinations and medication given.
|Aflatoxicosis||Aspergillus flavus/parasiticus||Maize ,Groundnuts, Rice, Cotton seed, Millet, Sorghum and other ingredients|
|Ochratoxicosis||Aspergillus ochraceus||Maize,peanuts,Soybean Rice, Millet, most small grains and other ingredients|
|T-2 toxicosis||Fusarium||Maize,Rice,Wheat, Barley, Oats, Rye, Sorghum and other ingredients|
|Citrinintoxicosis||Pencilliumcitrinum||Maize, Rice and other cereal grains|
|Oosporein||Chaetomiumtrilaterale||Maize, ground nut cake Rice, other grains and ingredients|
|Moniliformin||Fusariummonliforme||Unharvested maize,stored maize with high moisture Soy bean,Wheat, Sorghum and Barley|
|Fumonisins||Fusariummoniliforme||Maize, corn based feeds|
|Fusarochrmanon||Fusarium species||Corn, rice|
Synergy between mycotoxins:
It is uncommon to find a single mycotoxin occuring in field condition. Generally, they occur in synergistic combination of two or more having potentially devastating effect though present in low levels. Fungi producing different mycotoxins require different environmental conditions. As the feedstuffs are exposed to varied climatic conditions in the field during harvest, transit, storage, etc. favour the production of toxins by respective fungal species. Grains and oil seed byproducts which are commonly used in poultry diet are derived from different climatic conditions. Hence the compound feed made of these ingredients can have combination of different mycotoxins. It is well proven fact that combined effect is more devastating than individual mycotoxins.
though data with regard to their impact on intestinal functions are more limited. However, intestinal cells are the first cells to be exposed to mycotoxins, and often at higher concentrations than other tissues. In addition, mycotoxins specifically target high protein turnover- and activated-cells, which are predominant in gut epithelium.
The intestinal epithelium is exposed to the entire content of contaminated feed and is the first target mycotoxins. The rapid appearance of most mycotoxins in the circulation clearly indicates that the majority of the ingested toxin is absorbed in the proximal part of the GIT. Mycotoxins can therefore compromise the intestinal epithelium either before absorption in the upper part or throughout the entire intestine by non-absorbed toxins. Gut epithelium is exposed to a very high proportion of the toxin ingested.This makes the mycotoxins available again via the bile in the entero-hepatic cycle, resulting in reabsorption and a prolonged retention time in the GIT. The absorption and fate of mycotoxins within the GIT provides evidence that the intestinal epithelium is prone to the toxic action of these toxins.
Mycotoxin metabolism can occur in both the liver and the digestive tract. Intestinal metabolism, whether be in the gut epithelium or by gut microorganisms, may limit the toxic effects of mycotoxins within the GIT. This is especially true for ruminants which are able to convert many mycotoxins into non-toxic metabolites.
Aflatoxin requires metabolism to its toxic metabolite as epoxide. While this activation has been largely described in the liver, AFB1 metabolism to the reactive epoxide also takes place in the intestinal tract
For challenges associated with the gastrointestinal tract, a large part of the reduction in growth was due to an increase in maintenance requirements, suggesting digestive and metabolic changes (repair of damaged tissues, maintenance of the integrity of the GIT, as well as metabolic cost associated with the stimulation of the immune system
Nutrition and digestibility
Research points to a direct and/or indirect effect of mycotoxins on the nutrient quality, digestibility and/or absorption. There is a close association between production performance and digestive activity.
Very low doses of AF(Aflatoxin) B1 (20 and 40 μg/kg) reduced the apparent digestibility of crude protein by 8% to 13%. Similarly, dietary AF was suggested to increase the amino acid requirements, Net protein utilization, apparent digestible (ilealdigesta) and metabolizable energy (excreta) were also evaluated by scientists and AF was shown to reduce energy utilization
The measure of apparent digestibility reflects the net effect of all digestive and absorptive processes along the digestive tract. Several reports have concluded that enzyme activity is altered following AF consumption. birds fed with known quantity of AF, on the duodenal activity of amylase revealed higher activity of amylase, trypsin and chymotrypsin in both the pancreas and duodenum However, digestion of nutrients was not enhanced in the intestine suggesting that a compensatory response to a nutrient deficiency during aflatoxicosis.
Similarly in poultry, either low or moderate levels of DON in feed, as well as its combination with other Fusarium toxins were able to lower the absorptive surface area through a decrease of villus height in the duodenum and jejunum
Various nutritional manipulations can minimize the adverse effects of mycotoxins :
- Crude protein – As the mycotoxins affect protein and amino acid metabolism, increasing the dietary levels of protein can minimize the ill effects specially when contaminated with aflatoxin. However, it is very costly approach.
- Supplementing methionine and other sulphur amino acids over and above the requirement can protect the chicks from growth depressing effect of aflatoxin.
- Vitamin D3 supplementation can minimize the adverse effect of aflatoxins such as leg weakness, poor egg shell quality.
- Vitamin E and Selenium are involved in formation of glutathione peroxidase which, is vital for cellular detoxification. Effects of T2, OA and aflatoxins are partially counteracted by such antioxidant mechanism of vitamin E and selenium.
- Additional allocation of lipotropic agent like choline helps in minimising liver damage.
Effect of mold contamination on the nutritional value of stored maize
|ME (Kcal/kg)||CP (%)||Fat (%)|
|% Loss in nutrient||4.6||6.7||62.5|
|Effect of mycotoxin on Vitamin metabolism (Plasma Vit:ng/ml)|
Aflatoxins are produced by certain strains of Aspergillus flavusand Aspergillusparasiticus. Cropsin tropical and subtropical areas are more subject to contamination than those in temperate regions, since optimal conditions for toxin formation are prevalent in areas with high humidity and temperature.
Toxin-producing fungi can infect growing crops as a consequence of insect damage, and may produce toxins prior to harvest, or during harvesting and storage. The moisture content of the substrate and temperature are the main factors regulating fungal growth and mycotoxin formation. In starchy,
The minimum, optimum, and maximum temperatures for aflatoxin production are 12° C, 27° C, and 40-42° C, respectively.
Groundnut seeds may be invaded by A. flavusbefore harvest but others are more likely to be invaded very rapidly in post-harvest period that is the “high hazard” time for aflatoxin production. Damage caused by insects also aid in the infection process because insects may carry fungal spores. Insect injury in ears of maize in the field may also be accompanied or followed by infection with A. flavusand by aflatoxin formation before harvest
The presence of mycotoxins in dried distillers’ grains with solubles (DDGS), a by-product of bioethanol production from maize, has been a matter of concern due to the increasing global utilisation of this ingredient in animal feed
The term aflatoxins usually refers to 4 compounds named B1, B2, G1 and G2, which occur naturally in plant products; maize, groundnuts as well as many other foodstuffs and feeds. The relationship between the chemical structures of different aflatoxins and their biological activity was investigated and found that b1 is more toxic than other forms of aflatoxin.
While oil is removed from oilseeds, most of the aflatoxins are found in the oilseed meal. Small amounts remaining in the crude vegetable oil used mainly for the soap.
Absorption: Although quantitative data on absorption are not available at present, aflatoxins being fat-soluble are rapidly absorbed in alimentary tract. When poultry were fed rations containing aflatoxins, residues were detected in the liver, kidney, muscle and adipose tissue. The liver contained the highest concentration.
The liver is mainly affected in all outbreaks and also in experimental studies on animals. The acute liver lesions are characterized by necrosis of the hepatocytes and biliary proliferation, and chronic manifestations may include fibrosis. The acute toxicity and carcinogenicity of aflatoxins are greater in male than in females. Hormonal involvement may be responsible for this sex-linked difference.
Metabolic transformation and activation
Mycotoxin Metabolism is divided into two phases.The basic biotrasformation reactions are divided into Phase Icosisting of oxidation,reduction and hydrolysis and Phase II in which metabolic end products are conjugated with aminoacids, glucoronic acid or glutathione to facilitate excretion.
With one exception, all primary biotransformations of aflatoxin B1 involve its conversion to hydroxylated metabolites and are detoxified by conjugation with taurocholic and glucuronic acids prior to excretion in the bile or urine. The conversion in the liver of aflatoxin B1 to aflatoxicol is unusual in that, unlike other biotransformations that are catalysed by liver microsomal enzymes however the formation of aflatoxicol can be inhibited by sex hormones
The formation of the epoxies of aflatoxins is probably the more important form of metabolic activation facilitated by microsomal enzymes of liver. The metabolite is highly reactive, binds covalently to DNA. Aaflatoxin is activated on the outer nuclear membrane to a form that inhibits RNA polymerase and RNA synthesis. The permeability of mitochondria and lysosomal membranes increases. Many other metabolic functions are inhibited, including protein synthesis, enzyme induction. It has been shown that aflatoxins have immuno suppressive properties, probably related to their inhibitory effect on protein synthesis. Aflatoxins have been found to reduce resistance to infection by Pasteurellamultocida, Salmonella spp., Marek’s disease virus, Coccidiaetc
Ochratoxins are produced by several species of the fungal genera Aspergillus and Punctilion. These fungi are ubiquitous and Ochratoxin formation by Aspergillus species appears to be limited to conditions of high humidity and temperature, whereas Pencilliumspecies may produce ochratoxin at temperatures as low as 5°C.
Ochratoxin A has been found in maize, wheat as well as in many other food products.
Ochratoxin A has been found to be nephrotoxic in all species of animal. Impairment of glomerular and tubular function was also observed. Acute necrosis and “visceral gout” was observed in chickens exposed to high levels of ochratoxinA.Ochratoxin A acted synergisticallywith another nephro-toxic mycotoxin, citrinin.
Biochemical effects: Ochratoxin A affects the carbohydrate metabolism : the decrease in liver glycogen and associated with an increase in serum glucose levels
Asorption: Ochratoxin A was absorbed mainly in the stomach.
Uchangedochratoxin A were found in all tissues investigated (kidney, liver and muscle), the highest levels occurring in the kidney. It has been shown by in vitro studies that ochratoxin A binds to serum albumin. Ochratoxin A gets converted into ochratoxin alpha and phenylalanine and excreted in urine and faeces.
Trichothecene toxins belong to a group of closely related chemical compounds produced by several species of Fusarium. More than 30 trichothecene derivatives have been isolated from fungal cultures, but, so far, only 4 have been identified as natural contaminants of foodstuff T-2 toxin, nivalenol, deoxynivalenol, (vomitoxin), and diacetoxyscirpenol.
Extensive necrosis of the mucosa in the small and large intestine, damage to bone marrow cells in laying hens, reduced egg production and immunosuppression due to decreased leukocyte count are noticed with T-2 toxicity
Zearalenone, a metabolite produced by various species of Fusarium, has been observed as a natural contaminant of cereals, in particular maize. has been shown to produce estrogenic effects in animals, and field cases of a specific estrogenic syndrome in pigs and of infertility in cattle Zearalenone has been encountered as a natural contaminant, particularly in maize, but occasionally in other cereals and in feedstuffs. Zearalenone is associated with oestrogen syndrome in swine, however no effects on egg production were observed when laying hens.
In a nutshell:
- Mycotoxins are often present at very low levels (ppb)
- Mycotoxin content is not related to the amount of mould present
- Mycotoxins are not evenly distributed in the feed
- Mycotoxins could develop during any point of feed processing
- Mycotoxins can continue to be produced in storage.
- Lowering body weight gain and feed consumption, reduction in nutrient absorption and retention.
- Low or high mortality depends upon dietary toxin levels.
- Enlargement of liver and kidney but reduction in size of bursa.
- High concentration of faecal fat, leg weakness, decreased breaking strength of bones, poor pigmentation of skin (in broilers) and the egg yolk.
- In adult layers, increase in number of immature and shrivelled ova, poor shell quality, atrophied oviduct, haemorrhagic and pliable liver is observed.
- Interfere with Vit D metabolism affecting eggshell strength, egg production and eggquality
- Impaired ovary development
- In adult breeding males, reproductive performance is adversely affected in aflatoxicosis.
- Intestinal development is altered
- Biochemical changes: viz, decreased prothrombin, plasma calcium and iron levels, lower pancreatic lipase, trypsin and amylase levels as well phosphorus & copper metabolism also gets altered
- In poultry, low levels of toxins cause considerable immuno-suppression. Mycotoxin induced immunosuppression may be manifested as depressed lymphocyte activity, suppressed antibody production and impaired macrophage function
- Reduced vaccine efficacy
Permissible level of Mycotoxin:
Poultry complete feeds: 20 ppb
However permissible level cannot be safe level due to following reasons:
- Mycotoxin interaction i.e. synergistic effect
- Nutrition &Management vary
- All birds are not equally susceptible
- Stress aggravates the toxicity
- At lowest level immunity is seriously affected.
|U.S. FDA Levels for Aflatoxins|
|All products, except milk, designated for humans||20|
|Corn for immature animals and dairy cattle||20|
|Corn for breeding beef cattle, swine and mature poultry||100|
|Corn for finishing swine||200|
|Corn for finishing beef cattle||300|
|Cottonseed meal (as a feed ingredient)||300|
|All feedstuff other than corn||20|
Mitigation of mycotoxins
Some of the critical control points in a feed mill would be:
- Storage bins and warehouses
- Pellet coolers
- Feed storage silos
Critical control points at the farm level include:
- Feed bins and feed bin cleaning
- Bagged feed and type of bag material
- Feed equipment
- “Old feed” returns to the mill
- Cleanout procedures
- Litter management
- Drinker management and water quality
Mould Inhibitors and toxin binders
Mycotoxin decontamination of feed is a major task in the poultry industry globally.
It is generally recognized that in many parts of the world climatic conditions are such that controlling the growth of mould and fungi is extremely difficult. Feed manufacturers have increasingly incorporated mould inhibitors and toxin binders in their diets or applied them to raw materials in storage. Once contaminated raw materials are identified, many companies manage the problem through diluting the affected ingredients to reduce levels in the finished feed. This practice is valid but does not completely eliminate toxic effects.
Adsorbent compounds have been utilized to ameliorate mycotoxins in poultry
feed. The theory is that the binder decontaminates mycotoxins in the feed by binding them strongly enough to prevent mycotoxin absorption across the digestive tract and limited exposure to visceral organs.
Mycotoxins are metabolites of various fungus and chemically classified as polar organic compounds. Therefore, they can be effectively deactivated by making it irreversibly adsorb onto clay surface with mycotoxin-clay through dipole-ionic interactions.
Mineral clay such as aluminosilicates specially Hydrated sodium calcium aluminosilicate (HSCAS) has been found to more effective. The molecular surfaces of these additives, when saturated with water, attract the polar functional atomic structure of the mycotoxin and trap it against its surface. This isolates the mycotoxin from the digestive process and thereby prevents is from entering into circulation. They appear to have little or no beneficial effect against vomitoxin, T-2, Ochratoxin and DAS. MOS can effectively bind various toxins and activated charcoal nonspecific binder is good for Ochratoxin& pesticides.
The ideal features of a good binder are :
- Ability to bind a wide range of mycotoxins
- Low effective inclusion rate in feed
- Rapid and uniform dispersion in the feed during mixing
- Heat stability during pelleting, extrusion and during storage
- No affinity for vitamins, mineral or other nutrients or additives
- High stability over a wide pH range
Bentonites, zeolites, clinoptilolites and various others that are often not completely characterized. The clay group is a subcategory of the phyllosilicates. Bentonite is a general clay material primarily montmorillonite as the main constituent. All are generally classified as hydrated sodium calcium aluminium magnesium silicate hydroxide(HSCAS)
Having said this not all clay exhibits this property. The strongest irreversible binding happens if the criteria:
- Surface area,
- Porosity & Size of pores,
- Cation exchange capacity,
- Surface modification and Swelling
Surface area of the clay particles, which in turn depends on the particle size, which also can be expressed as number of particles per gram of clay. Higher the number of particles higher the surface availability.
Quarternisingthe clay us new technology wherein dipole-charge interaction can be made stronger by organically modifying the clay using long chain alkyl quaternary ammonium salts. The cetyl parts helps in enhancing dipole-dipole interactions, while ammonium part of the modifier holds on to the clay by replacing cations like Calcium or Sodium. In a nutshell, quarternising alters the structural arrangements of bentonite layers for better CEC and higher adsorption.
Several new toxin binders are studied and provide good results when used in combination
There are huge range of commercially available binders, with overwhelming choices and prices. The choice of mycotoxin binders depends on the risk assessment.