Mycotoxins are low molecular weight secondary metabolites produced by certain strains of filamentous fungi such as Aspergillus, Penicillium and Fusarium. Their presence in animal feed can have serious negative effects on animal health and performance. The effects of mycotoxins in poultry feed depend on the specific mycotoxin or mycotoxins present, the level of contamination, the length of time the animal has been consuming the mycotoxin(s), and the animal's age, sex, and level of stress.
The mycotoxins of most concern due to their toxicity and occurrence are aflatoxin, vomitoxin, ochratoxin, zearaleone, fumonisin and T-2 toxins. They cause significant economic losses in animals due to reduced productivity, increased disease incidence, chronic damage of vital organs and decreased reproductive performance.
No region in the world escapes the problem of mycotoxins and its estimated that there are about 300 harmful mycotoxins. Food and Agricultural Organisation (FAO) estimates that about 25% of the world crops contain mycotoxins.
At the IHSIG conference, recently organized in Rome – Italy, an increase in the occurrence of mycotoxins worldwide and an increase in the prevalence of individual toxins in some regions was shown. Fumonisin levels rose significantly, especially in the southern hemisphere and have overtaken DON (Deoxynivalenol) as the most commonly detected mycotoxin worldwide.
In line with the findings of the 2017 report, significant geographical differences in the presence of certain mycotoxins can be seen. DON/Vomitoxin remained the most common detected mycotoxin in North America, reaching 67% of total samples. In Asia, 96% of corn samples tested positive for fumonisins. Aflatoxin remains a topic in Asia, with 44% of prevalence in finished feed. DON remains the most prevalent mycotoxin found in Europe.
The problem of mycotoxins does not just end in animal feed or reduced animal performance; many become concentrated in meat, egg and milk of animal and can pose a threat to human health.
Mycotoxins relevant in poultry production
Aflatoxins (AF) are the most well known mycotoxins including Aflatoxin B1, Aflatoxin B2, Aflatoxin G1 and Aflatoxin G2, being considered as the four major AF produced in feedstuffs. It is agreed only 4 species of fungi produce: Aspergillus flavus, A. parasiticus, A. nomius, A. pseudotamarii. First signs of an AF problem is decreased feed intake and depending on the levels present, losses can result from deaths, reduced growth rates and poor feed conversion.
While young animals are most susceptible to the effects of AF, all ages are effected whereby the mycotoxin can cause liver damage, kidney disorders, gastrointestinal dysfunction, reduced productivity, leg and bone problems and reduced feed utilization. Evidence suggests that immunosuppression caused by AF results in many disease outbreaks, vaccination failures and poor body titers.
In poultry, ducks are the most sensitive, followed by turkey, broiler and layers.
Ochratoxins are produced by fungi belonging to the genera Aspergillus and Penicillium whereby Ochratoxin A (OTA), mainly a contaminant of cereal grains, is the most prevalent one. It is primarily nephrotoxic and in terms of LD50, duckling appears to be the most sensitive species to OTA followed by broiler chicks, White Leghorn chicks, Turkey poults and Japanese quail chicks.
Signs of OTA toxicity in poultry include weakness, anaemia, decreased feed consumption, poor feathering, reduced growth rate and egg production. At higher dosages diarrhea, tremors, other neural malfunctions and excessive mortality can be observed.
The Fumonisins (FUM), are a group of mycotoxins originally isolated from Fusarium moniliforme. Six different FUMS have been identified (A1, A2, B1, B2, B3, B4), however Fumonisin B1 (FB1) has been reported to be the most predominant one.
With respect to toxicity, in poultry relatively high levels are required to observe negative effects of FUM. The primary changes in chicks, ducks and turkeys were decreased body weight gain and liver pathology.
In vivo-studies showed no negative effects despite levels of 25 to 50ppm whereas levels of 100 to 400ppm were detrimental to the performance in the case of day old chicks. In turkeys, reduced feed conversion and weight gain was observed with 300ppm of Fumonisin B1. The reduction was 30% after 3 weeks when compared to control.
Tricothecenes is a group of toxic fungal metabolites produced by a number of species of the genus Fusarium and can be divided into 2 groups.
- Group A tricothecenes including T-2 toxin, HT-2toxin and diacetoxyscirpenol (DAS)
- Group B tricothecenes: doxynivalenol (DON or vomitoxin), nivalenol ( NIV) and Fusarenon-X
From all tricothecenes, T-2 toxin has been the most extensively studied tricothecene in poultry.
Toxic effects of tricothecenes include oral lesions, growth retardation, abnormal feathering, decreased egg production and egg shell quality, regression of the bursa of Fabricius, peroxidative changes in liver, abnormal blood coagulation.
The presence of oral lesions in poultry is generally regarded as the primary means of diagnosing tricothecenes toxicoses in the field.
In general, contaminated feeds usually contain more than one mycotoxin. Discussing interaction among mycotoxins, from a meta-analysis of publications (>100), Grenier and Oswald (2011) observed that a combination of mycotoxins, at concentrations that individually should not cause negative effects, may negatively affect animals.
Counteracting mycotoxins with mycotoxin binders
Mycotoxin binders (adsorbing or sequestering agents) are large molecular weight compounds that are able to bind the mycotoxins in the gastrointestinal tract of the animal. In this way, the toxin binder complex passes through the animal, and is eliminated via the feces. This prevents or minimizes the exposure of animals to mycotoxins. Mycotoxin binders are mainly divided in silica-based inorganic compounds or carbon-based organic polymers (EFSA, 2009).
It is important to note that binders will not bind mycotoxins in dry feed as binders need an aqueous substrate to bind toxins. Also explains why the binder will not mitigate the initial toxic effect immediately after feed ingestion.
The inclusion of clay-based materials in the diet of animals has been widely adopted for reducing toxin bioavailability and exposure from contaminated feeds. These materials (and/or mixtures) are reported to contain smectite clays, zeolites, kaolinite, mica, silica, charcoal and various biological constituents.
Another inorganic sorbent is activated charcoal. In different studies it was demonstrated activated charcoal is an effective adsorbent of deoxynivalenol (DON), ZON, AFB1, fumonisin B1 (FB1) and OTA. Nevertheless, the major drawback in the practical use as feed additives, is its unspecific binding property. This way, it diminishes nutrient absorption, such as vitamins and minerals, and consequently impairs the nutritional value of feed.
To avoid nutrient parts get absorbed, it can be recommended using pyrolised charcoal. Compared to activated charcoal, pyrolysed charcoal is binding toxins but not the nutrients this due to fact that 10% only of the pores in pyrolysed charcoal are micropores. In activated charcoal, 80% of the pores can be classified as micropores.
Polymers are another group of inorganic mycotoxin binders. Several agents belong to this group, such as dietary fibre and polyvinylpyrrolidone (highly polar amphoteric polymer), but the most well-known is cholestyramine.
In vitro trials demonstrated this compound is an effective binder for FB1, OTA and ZON in vitro. Unfortunately, the cost of polymers high, limiting their practical use in animal feed production.
Preventing mould growth and subsequent mycotoxin production is essential to the feed manufacturer, livestock producer and for maximum animal performance. This makes there is an excellent potential for binders to help manage the mycotoxin problem and reduce toxic exposure to consuming animals.
Bart De Meue - freelance marketing
Commissioned by Sanluc International nv
1. Prevalence and effects of mycotoxins on poultry health and performance, and recent development in mycotoxin counteracting strategies.
Poultry Science | June 2015 | Vol 94 | Issue 6 | Pages 1298 - 1315
2. Mycotoxicosis and its control in poultry: A review
Journal of Poultry Science and Technology | January-March, 2014 | Vol 2 | Issue 1 | Pages 01-10
3. Effects of Mycotoxins in Animal Nutrition: a review
Asian Journal of Animal Sciences | 2011 | Vol 5 | Issue 1 | Pages 19-33
4. Mycotoxins and Their Effect on Poultry and Swine Production
PennState Extension | Pennsylvania State University – USA | November 29, 2018
5. Different methods to counteract mycotoxin production and its impact on animal health
Vlaams Diergeneeskundig Tijdschrift | 2013 | Vol 82 | Pages 181 – 190
6. Evaluation of Mycotoxin binders
Lon W. Withlow | North Carolina State University| Department of Animal Science