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By Dr H.V.L.N. Swamy, Alltech Canada

Mycotoxins are the secondary metabolites of moulds, which are ubiquitous in nature. Four genera of mycotoxin-producing moulds on a global scale include Aspergillus, Fusarium, Penicillium and Claviceps. The recent survey on Alternaria toxins from Argentina is certainly forcing us to include Alternaria mould into the above list. Depending on various factors, one or more of these moulds grow on crops while they are on the field as well as during storage.

There are close to 500 mycotoxins that have been identified to date, and undoubtedly there are many more to come. The immediate challenge that chemists around the world are facing is related to masked mycotoxins and the means and modes of analysing them so that their masked effects can be quantified. The objective, here, is to highlight the demonstrated effects of the key mycotoxins on poultry health and performance while referencing to their regional distribution. These include aflatoxins, ochratoxins, Type A trichothecene Fusarium mycotoxins, Type B trichothecene Fusarium mycotoxins, zearalenone, fumonisins, moniliformin, and ergot alkaloids. Classifying the mycotoxins to a specificregion has been curtailed in recent years due to the extended trading of grains and meals across the world, as well as appreciable changes in the global climatic conditions. Unexpected drought, rainfall and floods have added more mystery to the already complex issues of sampling and mycotoxin analysis. Nevertheless, the greater prevalence of a specific group of mycotoxins to a particular region can be generalised (Table 1).

Based on LD50 values (amount of mycotoxin required to kill 50% of test population), the order of severity for some of the mycotoxins is as follows: Ochratoxins > Diacetoxyscirpenol (DAS) > T-2 toxin > Moniliformin > Aflatoxins > HT-2 toxin > Neosolaniol > Deoxynivalenol (DON) (Table 2). Although aflatoxins are very well studied in poultry, ochratoxins, DAS and T-2 toxin are more toxic than aflatoxins.

Toxicity of some mycotoxins

The biggest challenge with mycotoxicosesis the non-specific nature of symptoms in poultry. This makes it very hard for the poultry producer to diagnose the problem and take appropriate actions. The symptoms of mycotoxicoses can also be similar to those arising as a result of poor management, nutrition and health. Hence it is quite common under commercial conditions to compare the mycotoxin results of poultry feed with the symptoms on the farm to confirm mycotoxicoses. Acute and chronic toxicities of some of the important mycotoxins in poultry are discussed here. The toxicity of mycotoxins generally depends on the dose and source of mycotoxins, and the duration of exposure.

1. Aflatoxins: Although 18 different aflatoxins have been identified, only aflatoxins B1, B2, G1 and G2 have been detected as natural contaminants of feeds and feedstuffs. There are discrepancies in the literature in terms of the minimum dose of aflatoxin that is required to cause toxicity in poultry. This can be attributed mainly to different sources of aflatoxins used in these studies. Most of the studies used either purified AFB1 or AFB1 from Aspergillus fungal culture but not naturally-contaminated feed. A broiler chicken study, however, has shown to reduce body weight at levels as low as 75 ppb aflatoxins. Reduced egg production and egg weight, and increased liver fat are the major signs of aflatoxicoses in laying hens, while poor hatchability and increased embryonic mortality were noticed in breeding hens. The greatest effect of aflatoxins on immunity is on the cell mediated immune response such as lymphocyte depletion, decreased delayed-type hypersensitivity, and modification of cytokine production. This can result in poor disease resistance and vaccine response. Aflatoxins can also lead to poor pigmentation in broiler chickens.

2. Ochratoxins: Although the ochratoxin group comprises 7 compounds, only ochratoxin A (OA) has been found as a natural contaminant of cereal grains. Kidneys are the major target organs for ochratoxins. Increased water consumption and manure moisture, swollen and pale kidneys, and secondary visceral gout are some of the specific symptoms of ochratoxicoses in poultry. Similar to aflatoxins they have been shown toreduce feed intake, lower egg production and weight, and negatively effect feed efficiency. Increased incidence of shell stains and meat spots have also been reported in commercial layers. OA impairs the ability of chickens to utilise dietary carotenoids for carcass pigmentation more severely than aflatoxins. As per the scientific literature, 0.5 ppm seems to be the minimum dose of OA to cause problems in poultry.

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