Lipopolysaccharides (LPS) constitute up to 75% of the structure of the cell wall of Gram-negative bacteria, being present at average 2x106 molecules of LPS/bacterial cell. LPS are a prerequisite for bacterial viability; they serve as a potential barrier toward antimicrobials at the outer membrane of Gram-negative bacteria. Figure 1 illustrates the structure of a lipopolysaccharide containing a pyrogenic lipid part embedded in the bacterial wall, an inner and outer core oligosaccharide, and an O antigen polysaccharide chain. Also called endotoxins, lipopolysaccharides are released upon bacterial replication or death (lysis). They are present everywhere in the environment including in the ground, air, water and the GI tract. Pigs are continuously exposed to them throughout their lives. In healthy animals, the intestinal and other epitheliums such as skin or lungs, represent an effective barrier that prevents their passage into the bloodstream. Once there, however, endotoxins can elicit strong immune responses, weakening immune systems and impairing performance. Severely pronounced immune response can lead to septic shock. In swine, endotoxins are known to cause dose-dependent increases in body temperature of 1°C to 1.5°C, reduced levels of activity/movement, lower feed intake, and severe anorexia. More frequent vomiting, salivation and chewing have also been reported.
Figure 1. Diagram of a lipopolysaccharide.
Effects on gut
The gut is the first line of defense against endotoxins and, if compromised via nutrition, stress or metabolic state, can result in increased endotoxin transport. Heat stress, for example, increases gut permeability. LPS can be absorbed through the intestinal epithelium to the general circulation through either the said paracellular or the transcellular pathway, being the first the most frequent. Transcellular transport happens trough receptor mediated endocytosis or diet fat micellar assisted permeation (Figure 2).
Figure 2. Enterocytes with tight junctions structure and actin filament supporting structure.
Source: Mani et al, 2013
PS is transported in the blood by LPS binding protein (LPB), synthesized in liver and gut epithelial cells as acute phase reactant, at lower extent transported by albumins; once bound is able to activate the specific receptor TLR4 and initialize the kinase cascade and the NF-KB transcription factor complex, this way several hundreds of genes are transcribed to start inflammatory response.
Once in the bloodstream, endotoxins are transported to the liver through the portal vein where a major portion of the detoxification process occurs. If the amount of endotoxin entering the gastrointestinal tract overwhelms the detoxification capacity of the liver, endotoxemia ensues.
Endotoxins cause an inflammatory cascade that increase a pig’s maintenance requirements (due to fever) that, coupled with reduced feed intake, means less energy is available for growth. One research study found that LPS-challenged piglets had a 13% lower average daily gain (Table 1) compared to the control group.
Endotoxins also impair feed efficiency. A recent study of common challenges in pig farms reported a reduction in feed intake of 3% due to parasitic infections, 4.1% due to poor housing conditions, 10.2% due to digestive bacterial infections, 17.3% because of respiratory diseases, 25.2% due to mycotoxicoses (mycotoxin-induced diseases) and 26.8% due to lipopolysaccharides.
Table 1. Higher inflammation and lower growth.
Source: Lieu et al., 2003
Environment and endotoxin exposure
While the main route for lipopolysaccharide exposure in swine is the gastrointestinal tract, the concentration of endotoxins in the air and dust should not be overlooked: endotoxins are a major component of biological dust. Air endotoxin levels are an important issue not only for the animals, but also for workers. A survey of pig production facilities has registered airborne lipopolysaccharide concentrations from 40.4 to 1.144 nanograms per cubic meter of air (Table 2). This reinforces the importance of good management regarding hygiene and dust levels on farms, and specific measures to protect workers such as wearing a fine dust mask.
Table 2. Total endotoxin air contamination in pig production facilities, stationary sampling.
Source: Øyvind Omland, 2002
Aggravation of endotoxin exposure
Major detoxification process for LPS is through a lipase present in macrophages, dendritic cells, neutrophils, liver cells and renal cortical tubule cells. Intestinal alkaline phosphatase, or IAP, is a brush–border enzyme that detoxifies directly lipopolysaccharides. IAP is modulated by presence in the diet of saturated or unsaturated fatty acids, with saturated increasing its presence. High caloric and high fat diets increase serum endotoxin concentrations and induce acute low-grade inflammation. Starvation, stress or disease can depress the expression and function of IAP—particularly in early weaning piglets—and result in high pro-inflammatory cytokine expression.
Lipopolysaccharides are able to increase a pig’s sensitivity to deoxynivalenol, a major mycotoxin that can cause feed refusal, vomiting, diarrhea, splay legs and weakened immune function. A synergistic effect was recently found between deoxynivalenol and lipopolysaccharides in induction of pro-inflammatory cytokines TNF-α and IL-1β in porcine alveolar macrophages. Endotoxins reduced the minimum dose of deoxynivalenol needed to induce cytokine response, increased its toxic effects, increased organisms’ sensitivity to the toxin and magnified the effects of even low concentrations.
Tips to reduce the risk of endotoxins.
- Avoid the introduction of pathogens through robust biosecurity
- Limit stressors linked to leaky gut, and conditioned diseases such as Pasteurella, Haemophilus, E. coli, Salmonella, Brachyspira, Lawsonia, etc.
- Provide proper nutrition, balancing appropriate protein and energy (fats)
- Avoid fasting after weaning
- Avoid mycotoxin contamination
- Use an effective endotoxin and mycotoxin deactivator
Biosecurity and hygiene can greatly help decrease the lipopolysaccharide challenge in farm animals, together with the awareness that a certain amount of endotoxin is always present. Some healthy behaviors can greatly help to reduce the risk of endotoxin challenge on the farm. In addition, the use of a selected feed additive that offers endotoxin protection can help mitigate the risks of a lipopolysaccharide challenge. Mycofix® is a multi-strategy mycotoxin and endotoxin deactivating feed additive that uses adsorption as a mode of action to effectively bind and prevent endotoxins from entering the bloodstream, mitigating the risk to animals. Figure 3 shows that even at low doses, Mycofix® is able to efficiently adsorb or bind a considerable percentage of endotoxin in the gut lumen, greatly decreasing its passage into the bloodstream. Other research has demonstrated this mode of action to be effective even in the presence of adsorbable mycotoxins such as aflatoxins.
Figure 3. Mycofix® counteracts endotoxins at low doses.