ISSUE FOCUS 22 FEED & ADDITIVE MAGAZINE April 2023 sue are not problematic. However, some factors can lead to a release of the endotoxins or translocation of endotoxins into the organism: 1. Stress Stress situations such as parturition, surgeries, injuries can lead to ischemia in the intestinal tract and translocation of endotoxins into the organism (Krüger, 1997). Other stress situations in animal production, such as high temperatures and high stocking densities, contribute to higher endotoxin levels in the bloodstream. Stress leads to a higher metabolic demand for water, sodium, and energy-rich substances. For a higher availability of these substances, the intestinal barrier’s permeability is increased, possibly leading to a higher translocation of bacteria and their toxins into the bloodstream. Examples: - Higher levels of endotoxins in pigs in an experimental study suffering from stress due to loading and transport, elevated temperatures (Seidler (1998) cited in Wilken (2003)). - Marathon runners (Brock-Utne et al., 1988) and racing horses (Baker et al., 1988) also showed higher endotoxin concentrations in the blood proportional to the running stress; thus, trained horses showed lower concentrations than untrained. 2. Lipolysis for energy mobilization If endotoxins, due to continuous stress, consistently get into the bloodstream, they can be stored in the adipose tissue. The SR-B1 (Scavenger receptor B1, a membrane receptor belonging to the group of pattern recognition receptors) binds to lipids and the lipopolysaccharides, probably promoting the incorporation of LPS in chylomicrons. Transferred from the chylomicrons to other lipoproteins, the LPS finally arrives in the adipose tissue (Hersoug et al., 2016). The mobilization of energy by lipolysis e.g., during the beginning of lactation, for example, leads to a re-input of endotoxins into the bloodstream. 3. Damage of the gut barrier In normal conditions, due to bacterial activity, endotoxins are present in the gut. Damage of the gut barrier allows translocation of these endotoxins (and bacteria) into the bloodstream. 4. Destruction of Gram-negative bacteria Another “source” for endotoxins is the destruction of the bacteria. This can be done on the one hand by the organism’s immune system or by treatment with bactericidal substances targeting Gram- bacteria (Kastner, 2002). To prevent an increased release of endotoxins, in the case of Gram-negative bacteria, a treatment with bacteriostatic substances only inhibiting the growth and not destroying the bacteria, or with bactericidal in combination with LPS-binding agents, would be a better alternative (Brandenburg, 2014). 5. Proliferation of Gram-negative bacteria As gram-negative bacteria also release small amounts of endotoxins when they grow, everything promoting their proliferation also leads to an increase of endotoxins: Imbalanced feeding High yielder cows e.g., are fed diets rich in starch, fat, and protein. Increased feeding of fat leads to a higher concentration of endotoxins in the organism, as the same “transporter” (scavenger receptor class B type 1, SR-BI) can be used (Hersoug et al., 2016) for the absorption of fat as well as for the absorption of endotoxins. In a study with humans as representors of the monogastric species, Deopurkar and co-workers gave three different drinks (glucose – 100% carbohydrate, orange juice – 92% carbohydrate, and cream – 100% fat) to healthy participants. Only the cream drink increased the level of lipopolysaccharides in the plasma. Infectious diseases Infectious diseases like mastitis, metritis, and other infections caused by gram-bacteria such as E. coli, Salmonella, etc. can be regarded as sources of endotoxin release. Decreased detoxification or degradation Main responsible organ: the liver
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