One of the problems with endotoxins is that they can be produced in the rumen. Not all types of bacteria produce endotoxins, just Gram-negative bacteria. The term Gram-negative is based on how they react to a Gram stain under the microscope. Gram-negative bacteria do not retain this stain mainly because their cell wall is of a different structure including the presence of lipopolysaccharides (LPS or endotoxins) on the outer membrane. When Gram-negative bacteria die, the endotoxins are released. During fast growth of such bacteria there can also be significant “shedding” of endotoxins.
Endotoxins are always present to some extent in the rumen, but at higher levels they can compromise the integrity of the gut wall and impact on animal health. Endotoxins are one of the risks of acidosis because as higher levels of grains are fed, there is a general shift from Gram-positive to Gram-negative bacteria. Figure 1 shows how if the rumen remains at a pH lower than 6 for a more prolonged time, the level of endotoxins increases significantly. Sub-acute ruminal acidosis (SARA) challenge is often described as the rumen being below 5.8 for more than five hours per day, thus SARA represents an endotoxin risk.
Figure 1. SARA and endotoxins. Increasing endotoxin concentrations (in EU endotoxin units/mL) found in rumens which had longer duration per day of pH below 6. Note the endotoxin axis is on a log scale so at 5 the endotoxin concentration is ten times as high as at 4. From Zebeli et al, 2012.
Endotoxins may impact on the tight junctions or cause apoptosis of epithelial cells increasing the uptake of undesirable substances into the blood stream. Endotoxins themselves are also able to enter the bloodstream and research suggests a link between endotoxins and laminitis (Figure 2) and other health issues. One of the key impacts of endotoxins is an inflammatory response which represents a waste of energy for the animal as well as cell damage leading to health issues. Figure 2 shows how the Biomin® Bioprotection Mix in Mycofix® can reduce some of this damage. The response to endotoxins can also reduce appropriate immune response thus increasing disease susceptibility.
Figure 2. The link between endotoxins and laminitis in cattle and horses. Endotoxins (LPS) in a “ex vivo, in vitro” horse hoof experiment reduced the force required to separate layers of the hoof (indicative of laminitis). The asterisk indicates a statistically significant effect (P < 0.05). The claw material was unaffected when the Biomin® Bioprotection Mix was added.
The high osmolarity due to soluble carbohydrate levels associated with SARA may increase the amount of endotoxins crossing into the bloodstream. The high osmolarity leads to increased water flow from the bloodstream resulting in some dislodging and then death of epithelial cells allowing increased uptake of endotoxins and other undesirable substances, such as mycotoxins.
Mycotoxins and Endotoxins
Some mycotoxins such as the common trichothecenes can also have an impact on the intestinal barrier function and so increase the risk of endotoxin uptake into the bloodstream. Similarly, the negative effect of endotoxins on the rumen epithelium may increase the uptake of mycotoxins increasing the risk to the animal of even hard to absorb mycotoxins such as fumonisins. Both mycotoxins and endotoxins can trigger inflammatory and immunosuppressive effects (through reducing response or directly affecting immune cells) and both toxin types impact upon, and also be exacerbated by, liver damage.
The Effect of Heat
There is a strong link between heat stress and endotoxins. Heat stress increases blood flow to the skin at the expense of the rumen. This deprives epithelial cells of necessary oxygen and allows toxic substances to accumulate. Endotoxins uptake can increase through these damaged cells. Heat stress can also increase the impact of mycotoxins. And both mycotoxins and endotoxins can increase and prolong the negative effect of heat stress.
Management of Endotoxins and Mycotoxins
Management should include steps to reduce heat stress and to balance the diet according to the different demands of productivity and rumen condition. Mycofix® Plus has three strategies to help overcome the combined effects of endotoxins and mycotoxins. An effective binding component can adsorb endotoxins and mycotoxins simultaneously with high efficacy (Figure 3).
Figure 3. Simultaneous binding of aflatoxin and endotoxins. In vitro adsorption efficacy of the Mycofix® Plus binder (0.02%) component on aflatoxin (4000 ppb) remains the same in the presence of a high level of endotoxin at 500 EU/mL (see left hand side) and endotoxin (LPS) binding was also similar in the presence of aflatoxin (see right-hand side).
In addition to adsorption, a unique and effective biotransformation approach for the difficult to bind mycotoxins such as trichothecenes is important to address the direct effects in the animal and their indirect intensifying of endotoxin damage. The third strategy of Mycofix® Plus is to provide protection for the vulnerable epithelial cells, liver cells and immune cells with research-proven bioprotection derived from phytogenic and algal ingredients.
References are available upon request from the author.