Pig lungs, gut both affected by fumonisins
Many are familiar with the negative impact of fumonisins on the lungs of pigs. However, even low fumonisin contamination can compromise the barrier function of the intestinal tract.
Fumonisin contamination in pig diets is most commonly derived from corn contaminated with Fusarium verticillioides and Fusarium proliferatum. From a recent mycotoxin survey (2013), we found 75 percent of 749 analyzed corn samples contained up to 23,180 ppb of fumonisins (U.S. corn, Table 1) with an average of positive samples of 2,158 ppb, whereas only 10 percent of 319 wheat samples (average of positive samples: 587 ppb) and 9 percent of 56 barley samples (average of positive samples: 844 ppb) were tested positive for fumonisins.
Similar to other fusariotoxins, the occurrence of fumonisins is ubiquitous and not limited to a specific climate. In Central European countries, 53 corn samples were analyzed with a positivity of 47 percent, with an average of positive samples of 443 ppb and 2,241 ppb maximum found. However, the highest contamination levels are found in tropical and sub-tropical regions. In Southern European countries, the contamination of corn with fumonisins was significantly higher: 91 percent of all analyzed corn samples tested positive for fumonisins, with an average contamination of 2,594 ppb and a maximum as high as 20,260 ppb!
Interestingly, these values from Southern Europe are very similar to values found in Brazil, a country where fumonisins have been considered a major problem for several years now. In 2013, 92 percent of 99 Brazilian corn samples were contaminated with fumonisins up to a level of 15,140 ppb and an average contamination of 3,052 ppb. Results of this comprehensive and detailed mycotoxin survey underline again that fumonisins are a potential contaminant of corn worldwide, with levels that can reach perturbing levels even in Europe.
How do fumonisins affect pigs?
Fumonisins exert their main toxic effects by impairing the production of complex sphingolipids that are necessary components of nerves, muscles and membranes. Swine, besides horses and rabbits, are the species most affected by the detrimental effects of fumonisins. The reason for different sensitivities between species lies in the different absorption of fumonisins in the gastrointestinal tract and, furthermore, different metabolization. In pigs, intoxication with high doses of fumonisins leads to porcine pulmonary edema, which results from the capacity of fumonisins to decrease cardiac contractility and increase mean pulmonary artery pressure. However, low contaminations of fumonisins (5 ppm) predispose pigs to lung pneumonitis. Toxic hepatosis can occur in the presence of porcine pulmonary edema but also without any visible effect on the lung.
Do fumonisins impact the integrity of the gastrointestinal tract of pigs?
The guidance value for fumonisin B1 + fumonisin B2 for complete feed for pigs taken from the respective regulation in the European Union is 5000 ppb. This might seem high compared to the maximum tolerated value of aflatoxin B1, which is 20 ppb. This is partially due to the low absorption of 3-6 percent fumonisins in the gastrointestinal tract. On the other hand, this low absorption of fumonisins leaves the gut exposed to a substantial part of the original contamination. In recent years, the impact of fumonisins on gut health has been investigated.
In in vitro experiments with porcine intestinal epithelial cells, fumonisins reduce the barrier function of those cells (Figure 2). Exposure to fumonisins for 10-15 days leads to a decrease in the trans-epithelial electrical resistance, a parameter that is used to prove the negative impact on the integrity of the barrier formed by the intestinal epithelium. Additionally, fumonisins also exert a cytotoxic effect on porcine intestinal epithelial cells, an effect that is more pronounced when the respective cells are dividing. The intestinal epithelium acts as a barrier protecting the organism from chemical products, mycotoxins and also from microbial pathogens.
Consequences from the reduced intestinal barrier function by fumonisins include:
- Increased translocation of bacterial pathogens across the intestine
- Impaired bacterial receptors on the surface of epithelial cells
- Altered sealing function of the intestinal epithelial cells
- Reduced specific proteins of the junctions within the epithelia
This increase in membrane permeability due to fumonisins may not only lead to increased mycotoxin absorption in general but also increases the uptake of pathogens from the diet. Therefore, low dosages of fumonisins (6.5-13 ppm fumonisin B1) increase intestinal colonization by E. coli, decreasing the local inflammatory response and increasing the permeability of the intestinal epithelium.
Fumonisins in the diet also reduce the height of the intestinal villi, leading to villi fusion in the small intestine (Figure 2), thus compromising nutrient uptake.
From worldwide occurrence data, it is obvious that fumonisins are a common contaminant in pig feed. Contamination with fumonisins can induce intestinal damage and may have consequences for animal health. Furthermore, fumonisins are a predisposing factor to infectious diseases and can compromise nutrient uptake.