‘Low dose’ usually refers to a value that does not exceed the EFSA or US FDA guidelines, in contrast to ‘high dose’ that is normally used under laboratory conditions. Low doses of mycotoxins have the greatest impact on the gastrointestinal tract (GIT), leading to a series of negative effects on the digestive and immune systems, which are sometimes followed by different histopathological damages.
The GIT: First Line of Defense
The gastrointestinal tract is not only responsible for the conversion of feed into energy, but also provides roughly 70% of the immune defense thanks to its own innate and adaptive immune system. When mycotoxins are introduced in the organism with feed the first system they encounter is the gastrointestinal tract, regardless of whether they are absorbed or not. If the gastrointestinal tract is compromised, the immune system, gut microflora, and all digestive processes in general are affected. The effects of low concentrations of mycotoxins in the gastrointestinal tract include:
- decreased weight gain
- feed refusal
- lower feed efficiency
- lower digestibility
- immune suppression
Nutrients Digestibility and Histopathological Damages
Low concentration of mycotoxins have adverse effects on the digestibility of feed mostly due to the damages that these metabolites cause to intestinal cells. Experiments conducted on ducks fed with low doses of aflatoxin (Afla) showed up to a 13% reduction in the digestibility of proteins. These effects were even higher in the case of synergistic interactions between aflatoxin and ochratoxin A (OTA). Synergistic interactions between deoxynivalenol (DON) and fumonisins (FB) were observed to produce histopathological lesions and high immunosuppression in piglets (see picture). Low amounts of DON lead to a reduction in the intestinal viscosity in chickens. Reduced feed digestibility together with pancreatic and liver damages were observed in chickens exposed to low doses of aflatoxin and fumonisin B1 (FB1). Decreased feed conversion was also detected in pigs fed with low doses of FB1 and DON.
Weakened Intestinal Defense
Consumption of contaminated feed even at low doses has an immunosuppressive function, rendering animals more susceptible to pathogen infections. Examples include coccidiosis and salmonellosis in poultry and pigs. In studies, animals that were fed with low concentrations of DON, T-2 toxin and OTA were generally more susceptible to pathogenic infections. Low concentrations of mycotoxins were also proven to promote infection by reovirus in rodents.
Consequences on Gut Microflora
The gut microbiota is an essential component of the gastrointestinal tract: it modulates the immune response and plays an active role in the digestive processes. Because mycotoxins show antimicrobial properties, they can play a nefarious role in causing shifts in the gut microbiota population. This is particularly true for ruminants where such a shift could interfere with the fermentative capacity of the rumen. An example is bowel disease, where the bacterial composition of the gut microbiota is shifted from anaerobic to aerobic bacteria.
The gastrointestinal track is the system most affected by low doses of mycotoxins. In fact, chronic cytotoxic effects on the intestinal cells can compromise feed conversion and lead to immunosuppression. As a result, overall animal performances decrease drastically with time, leading to important economic losses. Foodstuff that is naturally contaminated could contain doses that are much higher than the recommendations and guidelines. Correct feed management and the use of a proven mycotoxin deactivating feed additive can protect animals and preserve profits.