Feedborne Mycotoxins Threat to Poultry
Mycotoxins are metabolites produced by molds (fungi) that infect crops before harvest and continue to multiply under suboptimal storage conditions. Grains with a high moisture content are particularly unstable, prone to mold and possible mycotoxin production. Excessive rainfall at harvest and during critical periods of the growing season can be a major contributor to mycotoxin contamination of feed.
The most important mycotoxin-producing fungi affecting poultry production include Aspergillus and Fusarium. The most important mycotoxins produced by fungi of the Aspergillus genus are aflatoxins.
The aflatoxin-synthesizing fungi, A. flavus and A. parasiticus, are considered tropical or subtropical molds that thrive in conditions of high humidity and heat. The impact of feed-borne aflatoxins on poultry production has been extensively studied and we have a good understanding of tolerance in various species of poultry. Due in part to the fact that aflatoxin is a potent liver carcinogen, human health and food safety concerns arising from the contamination of poultry products with aflatoxin are of concern. The analytical technique for aflatoxins in feed is very practical because the number of different compounds is small and can be analyzed simultaneously.
Fusarium thrives in more temperate climates, including much of the U.S. Corn Belt. Our knowledge of fusarium toxin poisoning in poultry is far less comprehensive than our knowledge of aflatoxin poisoning. This is partly because the sheer number of Fusarium toxins, over 100 of which have been chemically characterized, makes a comprehensive analysis of Fusarium toxins in feed impractical, if not impossible. The most common Fusarium mycotoxins include trichothecenes, a large group of structurally related compounds including deoxynivalenol (DON, vomitoxin), T-2 toxin, nivalenol , diacetoxyspirophenol (DAS) and over 100 others; zearalenone, an estrogenic compound; fumonisins and fusaric acid.
Analysis of mycotoxins in poultry feed
The main source of error in mycotoxin analysis is inadequate feed sampling. Appropriate sampling protocols have been developed and published to minimize this source of error. Another source of error is the possible presence of different chemical forms of mycotoxins that may escape routine analysis. Attention has been focused on the conjugated forms of mycotoxins produced by plants. This may be the result of detoxification of mycotoxins by plant metabolism, and it has been suggested that the presence of combined mycotoxins could be used for genetic selection of plants against fungal invasion.
Although the bound form of dexoyivalenol (DON, vomitoxin) was discovered many years ago, there is little information on the relative importance of bound and free mycotoxins in poultry diets. It is not known whether conjugated forms of mycotoxins are as harmful to poultry as the parent compound, but it has been shown that some conjugated mycotoxins can be hydrolyzed in the digestive tract of animals.
It must be concluded that until we better understand the frequency, toxicity and nature of conjugated mycotoxins, current mycotoxin analysis in poultry feed should generally be considered an underestimate of correct values. Therefore, at this time it is necessary to consider mycotoxin analysis of feed as providing only an approximation of the real hazard posed by feeding contaminated material to poultry.
Effects of co-feeding poultry with grains naturally contaminated with Fusarium toxins A series of studies have been carried out to determine the effects of co-feeding naturally contaminated feed (mainly maize and wheat) to different types of poultry. This was done to simulate the situation in commercial poultry production where the diet contains multiple mycotoxin contamination vectors. It was determined that the mycotoxins in these diets were mainly vomitoxin, with small amounts of zearalenone and 15-acetyl vomitoxin in addition to fusaric acid. Four distinct modes of action of fed mycotoxins were identified: (1) decreased cellular protein synthesis (2) decreased immunity (3) altered brain neurochemistry (4) damage to intestinal epithelial cells.
Decreased cellular protein synthesis results in gastrointestinal damage, including necrosis, gizzard erosions, hemorrhage, and nutrient malabsorption. Decreased hepatic protein synthesis reduces dietary amino acid availability, leading to increased uric acid synthesis as amino acids are oxidized for energy.
A number of Fusarium mycotoxins and aflatoxins have been shown to have immunosuppressive effects. This leads to increased susceptibility to disease, lingering health problems in the flock and possible failure of vaccination programs. Furthermore, disease symptoms caused by immunosuppression are not characteristic symptoms of mycotoxins. They are only indirectly caused by mycotoxins, which makes it very difficult to identify mycotoxins as pathogens that reduce flock health.
Combined mycotoxins of Fusarium in feed are pharmacologically active. This means they have drug-like properties due to their effects on the neurochemistry of the brain. The most reproducible effect observed was an increase in serotonin concentrations in brain regions. These changes alter behavior and include decreased food intake, loss of muscle coordination and increased lethargy.
fed a mixture of ingredients naturally contaminated with combinations of Fusarium toxins resulted in reduced growth during the growing season, elevated blood uric acid levels, breast meat discoloration, and immunosuppression. Changes in brain neurochemistry were also observed.
Feeding broiler breeders
a similar combination of Fusarium mycotoxin-contaminated materials to broiler breeders significantly reduces hatchability due to reduced shell thickness of fertilized eggs. Changes in brain neurochemistry were also observed. Diet had no effect on sperm quality. In a parallel study performed on broiler breeder pullets, immunosuppression was observed.
are very sensitive to feeding combinations of Fusarium toxins. Egg production and feed efficiency decreased, while blood uric acid concentration increased significantly. Elevated blood uric acid levels may be due to a reduced rate of protein synthesis in the liver. Immunosuppression was also observed.
turkeys are very sensitive to feeding of feed contaminated with high concentrations of Fusarium toxins, with significantly reduced growth rates even at the start-up phase, and some indicators of immunosuppression. Feeding lower concentrations of Fusarium toxin also reduces growth rate, increases blood uric acid levels and causes immunosuppression. This is combined with morphological changes in the small intestine and changes in brain neurochemistry.
It can be concluded that poultry are sensitive to combinations of feed-borne Fusarium toxins and feeding contaminated material should be minimized. The frequency of mycotoxin contamination in poultry feed appears to be increasing. This may be partly due to unfavorable weather conditions leading up to harvest in many parts of the world due to global climate change.
The complexity of modern poultry diets, including the increasing use of potentially contaminated by-products such as distiller's grains, increases the potential for toxicological synergy between combinations of mycotoxins, thereby increasing the likelihood of poultry responses to contaminated feed. seriousness.
The use of suitable mycotoxin binders may be the best short-term strategy to minimize the adverse effects of feed-borne mycotoxins in poultry feed. It is hoped that long-term strategies, such as improved quality control measures resulting from advances in analytical methods and plant breeding strategies to reduce the susceptibility of plants to fungal invasion, will help minimize mycotoxin challenges to the poultry industry in the future.