Impact of mycotoxins on intestinal health
The mycotoxins present in animal feed represent a very real threat to animal health. Even small amounts of mycotoxins can have a negative effect on gut health. This can make the animal more susceptible to infectious diseases.
Gut health is of major importance to maximize the health, welfare and performance of production animals. Cattle have traditionally been selected for optimum feed conversion and maximum body weight gain. However, the intestinal health of production animals is constantly challenged throughout the life of the animal by exogenous and endogenous stress factors. Among the most important exogenous stressors and safety risks for the future feed industry and the safety of the feed supply chain are mycotoxins.
Mycotoxins are secondary metabolites produced by toxigenic fungal species present in a multitude of cultures. Mycotoxin contamination appears throughout the crop life and processing cycle, from pre-harvest, harvest and post-harvest, as well as the process stage.
Dynamic crosstalk between intestinal epithelial cells, microbiota, local immune cells and nutrition is one of the main regulatory mechanisms for maintaining intestinal homeostasis. A disturbance of this homeostasis can lead to intestinal leakage, intestinal inflammation and dysbiosis. Ingestion of even low to moderate levels of mycotoxins disrupts this intestinal homeostasis. Understanding the different types of mycotoxin interactions with the gastrointestinal environment will be of major importance for future risk assessment and the organization of effective mycotoxin mitigation strategies.
Mycotoxins can negatively impact the gastrointestinal tract, making animals more susceptible to infectious diseases. Photo: Volodimir Zozulinskyi
Mycotoxins and leaky gut
The intestinal epithelium is a unique layer of cells lining the intestinal lumen that acts as a selective barrier, allowing nutrients and water from the intestinal lumen to be absorbed into the bloodstream. It is also the largest and most important barrier to prevent the passage of harmful substances present in the gastrointestinal tract, including foreign antigens, microorganisms and their toxins. Mycotoxins damage the intestinal barrier and cause intestinal leakage, modulating intestinal epithelial integrity and epithelial cell renewal and repair. By measuring transepithelial electrical resistance (TEER) and intestinal mRNA expression of genes encoding tight junction proteins, several in vitro and ex vivo studies indicate that mycotoxins such as deoxynivalenol (DON) and fumonisins (FUM) are able to increase the permeability of the intestinal epithelial layer of humans and animals, eg pigs and poultry. In addition, the viability and proliferation of animal and human intestinal epithelial cells can be adversely affected by mycotoxins.
Besides the negative impact of mycotoxins on intestinal epithelial cells, these toxins also impact on other elements of the intestinal barrier, such as the mucus layer, the secretion of antimicrobial peptides, chemokines and cytokines, and stress. oxidative. Exposure to DON and / or zearalenone (ZEN) mycotoxins decreased the number of goblet cells in the small and large intestine of pigs, which are of major importance for mucus secretion. In addition, sub-toxic doses of DON have been shown to reduce intestinal mucin production by specific decrease in levels of mRNA encoding membrane associated mucins in pigs and poultry. Several mycotoxins are also able to modulate the production of inflammatory intestinal cytokines. For example, intestinal exposure to DON induced a pro-inflammatory response with increased expression of interleukin (IL) -1α, IL-1β, IL-8 and tumor necrosis factor (TNF) -α.
Interaction between mycotoxins and the gut microbiota
The gastrointestinal tract is home to a dynamic microbial population that forms a complex ecosystem and maintains a symbiotic relationship with the host animal. The intestinal microbiota contributes to several physiological functions such as protective, structural and metabolic functions, regulation of host homeostasis by contributing to optimal digestion and absorption, regulation of energy metabolism, prevention of mucosal infections and modulation of the immune system. Disruption of gut microbial ecosystems during farm animal husbandry can dramatically increase the risk of disease. Few studies have demonstrated an impact of exposure to mycotoxins on the composition and diversity of the gut microbiota in humans and different animal species. It has been observed that the abundance of different bacterial families / genera such as Lachnospiraceae, Ruminococcaceae, Lactospiraceae, Faecalibacterium, Clostridiaceae Enterobacteriaceae, and Roseburia may be affected by exposure to mycotoxins. These changes in the composition of the gut microbiota could be associated with the impact of mycotoxins on digestive physiology, enterocyte viability and mucus production.
Increased susceptibility to infectious diseases
The negative impact of mycotoxins on gastrointestinal physiology and the immune system could also increase the susceptibility of animals to infectious diseases common in animal production, such as increased Salmonella Typhimurium in pigs by promoting bacterial invasion, trans-intestinal epithelial passage and absorption by alveolar macrophages. In addition, feeding pigeons with a diet contaminated with DON resulted in an increase in the percentage of losing pigeons. Salmonella compared to birds fed a control diet, 87% vs. 74%, respectively. In addition, feeding a diet contaminated with DON or FUM has been shown to be a predisposing factor for the development of Clostridium perfringens Necrotic enteritis induced in broilers. This coincides with the negative effects mentioned above on selected components of the intestinal barrier of the host chicken, namely villus height, tight junctions, mucus, oxidative stress and microbiota homeostasis. Recently, it has also been shown that DON also influences the infection profile of Campylobacter jejuni in broiler chickens. The co-exposure of DON in poultry feed and C. jejuni resulted in an improvement C. jejuni colonization in the intestine as well as an increase in intestinal permeability.
Susceptibility to disease
In conclusion, the ubiquity of mycotoxins in food represents a significant threat to animal health. Even low to moderate amounts of mycotoxins negatively impact gut health by causing gut leakage, gut inflammation, and influencing the composition of the gut microbiota. Therefore, the metabolic, physiological and immunological intestinal disturbances induced by mycotoxins mean that animals are more susceptible to infectious diseases.
References are available upon request.