Soccer pitch sized battle ground
The surface area of a healthy mature pig’s intestine can approach the size of a small soccer field. This is due to the finger-like projections, or villi, throughout most of the intestinal system and the microvilli on the surface cells of the villi. Healthy villi and microvilli can multiply the surface area by a factor of well over 1000. The extensive surface area of the gut wall is a constant battle zone under attack from harmful microbes trying to break through. In fact, the gut wall is the largest organ (and front line) of the animal’s immune system.
Big is beautiful for nutrient uptake
All livestock benefit from a massive surface area for efficient nutrient uptake. The condition of the gut wall is critical to maintaining surface area for nutrient absorption. The villi are constantly evolving and growing new cells to replace epithelial cells that have past their prime at a grand old age of two or four days. Villi are sensitive to the wrong microbes, changes in feed and other stresses. In fact, the length of villi in piglet intestines can be halved at weaning time, temporarily reducing the surface area available for absorption.
Yellow card: Deoxynivalenol
The villi are unfortunately also a major casualty of the ongoing challenge of common Fusarium fungi mycotoxins that occur in feeds. This can commonly impact on the surface area and nutrient absorption but there is an added issue; that the integrity of the barrier. Deoxynivalenol (DON) consistently tops the ranks of mycotoxins in the worldwide BIOMIN annual mycotoxin survey and even at low doses it impacts on the intestinal barrier and the immune system. The research into DON effects on the intestinal barrier and immune response demonstrates that this single mycotoxin impacts on just about every component of the animal’s defenses.
Figure 1. The effect of Fusarium mycotoxins including deoxynivalenol (DON) on gut wall integrity.
Source: Antonnisen et al., 2014
Figure 1 shows that DON reduces epithelial cell proliferation – these are the very cells that form the gut wall and line the villi. The production of protective mucus by goblet cells in the gut wall is also reduced by DON, leaving the animal more vulnerable to attack. Pathogen access through the gut wall is largely achieved between the cells and a major protection against this are the tight junctions between epithelial cells. DON reduces the thickness, complexity of strands and the overall integrity of the tight junctions. This has been shown to increase the level of invasion by a diverse range of pathogens including Salmonella Typhimurium, Clostridium perfringens (e.g. necrotic enteritis), E. coli and a wide range of other bacterial, fungal and viral diseases. Part of the tight junction effect is due to DON altering cytokine immune response expression. This triggers the tight junctions to open up and also causes a general inflammatory response.
Red card: Deoxynivalenol
DON can reduce beneficial bacteria in the intestinal flora (many of which have an important protective effect on the gut wall), and damage lymphocytes and other immune cells through damage to the cell membranes, chromosomes, and the DNA itself. DON also causes early death of villi and fusion of villi both reducing absorption of nutrients and resulting in an opportunity for pathogens to feed on damaged material and start to gain easier access to cells, and the circulatory system on the other side of the intestinal barrier. It can also reduce the height of villi and depth of crypts (the depressions in the gut wall at the base of the villi).
Terrible team sport
Other mycotoxins impact on gut wall integrity and have a synergistic effect increasing the damage caused by DON. This includes fumonisins such as fumonisin B1 (FB1) which acts against tight junctions and the Type A trichothecene which although somewhat similar to the Type B trichothecene DON, has some different specific modes of action (including degrading endoplasmic reticula and attacking mitochondria) thus exacerbating the effect of DON. Zearalenone (ZEN) is an interesting case where the mycotoxin by itself can sometimes increase protective mucus production but, in combination with DON, results in decreased mucus production as well as altered cytokines production.
A good defense
So if the pig intestine with healthy villi approaches the size of a soccer field, it invites the question of what is the condition of this soccer field. A nicely maintained cover and fully functional or a battered surface (Figures 2 and 3). The difference is one of surface area for nutrient absorption and barrier integrity for disease prevention and avoiding inflammation. Part of good maintenance is a mycotoxin counteracting product that deals with the deoxynivalenol issue and also has a broad action against the mycotoxins that amplify the effect of deoxynivalenol. A protective mix to aid liver function and protect the immune system makes sound sense also given the potential effects of small amounts of mycotoxin.
Figure 2. The healthier the villi, the closer a pig’s gut wall surface area gets to the size of a soccer field.
Figure 3. Fusarium mycotoxins including deoxynivalenol (DON) can degrade the surface of the gut wall
Photo: iStock/Joan Vicent Canto Roig