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The significance of mycotoxins in poultry production

Unusual global weather patterns and different feed storage practices are starting to influence the range of moulds and potential mycotoxin contamination of feed grains fed to poultry internationally.

What’s more, increased global trading of field-origin feed materials increases the chances that blends of grains will result in combinations of mycotoxins in any given diet. Accordingly the multiple mycotoxin threat in diets fed to poultry is now very real.

That was the message from Dr Trevor Smith from the University of Guelph, Ontario in Canada at the recent Country Fair Poultry event in South Africa.

“Mycotoxins are toxic secondary metabolites produced by moulds growing on crops in the field, during feed stock handling and during storage. The most commonly found mycotoxins include aflatoxin and the Fusarium mycotoxins and these can reduce productivity, impair reproductive performance and reduce the health status of poultry,” Dr Smith said.

He pointed out that aflatoxins commonly occur in feed materials grown in warm and humid conditions. “These mycotoxins are not considered to be a major problem in cold or more temperate regions, but caution must be exercised if feed raw materials are being imported from warm and humid regions.”

Focusing on the field-origin mycotoxins, Dr Smith discussed particularly the key Fusarium mycotoxins – the fumoninsins, trichothecenes, zeralenone and fusaric acid – all of which can impair poultry performance.

“Poultry are relatively resistant to the Fusarium mycotoxins – fish, dogs, pigs and horses are the most sensitive species – but these hidden toxic compounds can still alter metabolism and cause specific lesions if present at sufficient levels.”

Dr Smith explained that fumoninsins can inhibit the synthesis of membrane lipids and that 100ppm causes reduced growth rate in broilers. But the greatest threat presented by feed-borne fumoninsins is immune-suppression, he said.

The trichothecenes are a family of more than 100 structurally-related toxins and can cause feed refusal through altering brain neurochemistry by increasing tryptophan and serotoxin levels. The most common trichothecene is deoxynivalenol (DON). Fusaric acid exerts its adverse effect similarly and can work synergistically with DON to reduce feed consumption, loss of muscle co-ordination and lethargy.

“However, the trichothecenes are also dermal necrotic agents, which can cause lesions in the beak, necrosis of the tongue and gizzard erosion. They can also precipitate intestinal tract haemorrhages, ulcers and wet, sticky litter due to nutrient malabsorption.”

Moving on to the zearalones, Dr Smith said poultry are quite resistant to these oestrogenic Fusarium mycotoxins, although they can cause prolapses in layers.

Turning to strategies for preventing mycotoxicoses, Dr Smith highlighted a range of approaches such as dilution with sound grain, diverting contaminated crops to less susceptible species such as ruminants and the use of mould inhibitors like propionic acid. However, it was the use of inorganic and organic mycotoxin adsorbents on which he focused most attention.

“The inclusion of adsorbents in feeds is an effective mitigation strategy provided the level of dietary inclusion is appropriate for the degree of mycotoxin contamination. Adsorbents are high molecular weight, highly branched polymers that pass down the digestive tract intact and can adsorb small molecules including, but not exclusively, mycotoxins. If included to excess an adsorbent – particularly those of inorganic origin – will also bind desirable nutrients such as amino acids, vitamins and minerals,” he cautioned.

Inorganic adsorbents are silica-based polymers. Synthetic inorganic adsorbents include HCAS, which is specifically designed to be effective against aflatoxins. Natural inorganic adsorbents (clays) include zeolites, diatomaceous earth and bentonite.

Dr Smith concluded by highlighting the benefits of organic mycotoxin adsorbents.

“Organic adsorbents are carbon-based polymers; examples include activated charcoal, lignin and the glucomannan polymer extracted from the cell wall of yeast. The novelty of the yeast cell wall polymer is that it has a high surface area, which allows for practical levels of inclusion in poultry diets (0.5-2.0kg per tonne), whilst also minimising the potential for the adsorption of desirable nutrients and essential intestinal metabolites,” he said.