Mycotoxins are fungal contaminants found in all kinds of commodities intended for food and feed. If the intestine of broilers or layers becomes exposed to high concentrations of these toxins following ingestion of contaminated feed, the performance or flocks can be compromised and economic losses for poultry producers significant.
One of the mycotoxins most frequently found in agricultural commodities is deoxynivalenol (DON). This common inhibitor of protein biosynthesis also inhibits the synthesis of RNA and DNA and alters cell membranes. Hence, tissues of high protein turnover, such as immune organs, liver and small intestine, can be adversely affected upon DON exposure.
In poultry, the effects of DON are not always obvious, but even in those cases where chickens do not show clinical symptoms, they will eat less feed, and experience negative effects on immunity, hematology and other health parameters. This lowers performance and productivity and can lead to high economic losses.
Varied impacts on performance
Although immune impairment is considered the most important outcome of DON mycotoxicoses, other negative effects on growth, feed consumption and possible intestinal alterations are also results of the ingestion of this mycotoxin.
In general, the toxicity of DON is derived from its epoxide group, which is responsible for the binding of the toxin to ribosomes. This mechanism, known as ribotoxic stress, leads to protein synthesis inhibition. The toxicity of DON is also due to its ability to cross the intestinal barrier.
The mechanisms behind the impact of DON on the gut have been widely studied for swine, the most sensitive species to this mycotoxin, and only very limited information is available for poultry. In general, studies have shown that DON may lead to lower productivity and impaired immunity.
Cost of changed gut morphology
The epithelial surface of the intestine contains a large contact area for absorption of nutrients and xenobiotics. However, the intestinal epithelial cells are also involved in the regulation of inflammatory mechanisms and create an important barrier against invading pathogens.
Studies have shown that DON decreases absorption of glucose and amino acids in the small intestine of broilers and laying hens, such that the nutrient uptake is relocated to the intestinal distal parts. These same studies have shown that absorption of glucose and amino acids in chickens can occur in the large intestine.
In hens, DON intake led to a decrease in the weight of the small intestine. Feeding DON to broiler chickens also affected the gut wall morphology.
It was observed that the villus height and the crypt depth both in the duodenum and the jejunum were reduced when broilers were fed DON at different concentrations (7.5-10 mg/kg feed). These findings suggest that DON adversely affects the intestinal digestive and absorptive functions. In addition, intestinal epithelium cells need to regenerate continuously in order to maintain an effective barrier function, and it has been shown that DON can be responsible for reduced cell proliferation.
Greater disease risk
The damage to the intestinal barrier, in addition to other possible adverse toxic effects may increase the passage of pathogens, and researchers have shown that the intake of DON-contaminated feed is a predisposing factor for the development of necrotic enteritis in broiler chickens.
Necrotic enteritis in broilers caused by the Gram-positive bacterium Clostridium perfringens. The negative effects of DON on the small intestinal barrier can lead to impaired nutrient digestion and leakage of plasma amino acids into the intestinal lumen. This results in the availability of the necessary growth substrate for the proliferation of C. perfringens.
An increased intestinal barrier permeability after chronic exposure to DON may also result in intestinal inflammation. Protein synthesis inhibitors such as DON can up-regulate the gene expression of cytokines in the mouse model and, recently, it was confirmed that DON can affect the plasma levels of cytokines and interleukines in the jejunum of poultry.
Cytokines are proteins that regulate immune responses by influencing growth, differentiation, and activation of cells. Interleukines are a group of cytokines that play an important role in inflammation. Dysregulations of cytokine processes are thought to result in various pathological disorders.
The precise molecular mode of action of DON in poultry has not yet been fully elucidated. Its effects are not always revealed as clear clinical symptoms yet even if these are not present DON can lead to reduced feed intake, along with effects on immunity, hematology and health parameters.
Due to its negative impact on performance and productivity DON can result in high economic losses for poultry producers. A first step towards preventing these negative effects is the use of good agricultural practices and proper storage conditions. An effective mycotoxin risk management program is also essential in order to protect birds from the effects that mycotoxins have on health and performance.