ISSUE FOCUS 42 FEED & ADDITIVE MAGAZINE March 2024 Leaky gut was once all about pH but understanding now revolves around the wider impacts of microbiology, endocrinology, physiology and immunology. What is the connection between acidosis, leaky gut, and the challenge of endotoxins – particularly lipopolysaccharides (LPS) – that are absorbed through the gut wall to cause an inflammatory response? And what is the energetic cost to fuel this response? UNDERSTANDING ACIDOSIS Acidosis in cattle is a condition that arises primarily from the difficulty of feeding to meet the requirements of high genetic merit animals. It occurs when there is an overabundance of rapidly fermentable carbohydrates in the diet, which drives the growth of amylolytic bacteria, an increase in the hydrogen sink and lactic acid, leading to a drastic reduction in rumen pH. This acidic environment hampers the normal digestion of feed and can cause a range of health problems for cattle, including laminitis, liver abscesses, and a weakened immune system. Acidosis results in substantial financial losses for the beef and dairy sectors due to decreased production and treatment costs. STRESS AND LEAKY GUT One of the previously less understood consequences of acidosis is its impact on gut health. In a healthy gut, tight junction proteins, on the lateral side of enterocytes, prevent pathogens entering the digestive tract and prevent the gut from leaking bacteria into the lumen. During times of stress, for example heat stress, these tight junction proteins retract, making the gut more permeable. As well as events such as heat stress, it is thought that even a psychological stress can cause the retraction of the tight junction proteins. ENDOTOXINS: LPS CHALLENGE AND THE INFLAMMATORY RESPONSE Endotoxins are toxins produced by bacteria, with lipopolysaccharide (LPS) being one of the most wellknown. In the context of acidosis, when the gut wall becomes more permeable, LPS can cross from the rumen into the lumen of the gut. A potent stimulator of the immune system, LPS is a pathogen associated molecular pattern (PAMP), that causes a Toll-like Receptor 4 (TLR4) mediated inflammatory response. When LPS crosses the barrier of the gut, a local inflammatory response will be stimulated. In worse cases, the LPS will enter the blood stream, and in the worst cases, the inflammatory response can become systemic. This inflammatory response is a necessary defence mechanism designed to protect the body from infection. However, when triggered repeatedly or excessively, as in cases of leaky gut due to acidosis, it can become harmful to the animal's health. During LEAKY GUT AND THE COST OF INFLAMMATION Dr. Sophie Parker-Norman Head of R&D and Technical Volac International
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