Peptidoglycans – impact on intestinal integrity

The greatest threats to efficient and profitable broiler performance are those that go unobserved - peptidoxglycans fit this category.

ROLANDO VALIENTES* briefly reviews the issues concerning the development of the intestinal microbiota and its relationship to the immune system of the host.

The gastrointestinal tract (GIT) is the system with the fastest development in broilers. All the nutrients that support the other systems in the animal are absorbed in the gut. The GIT is also an important barrier against pathogens, thus fulfilling the relevant functions of nourishing and protecting the animal. The GIT has been studied for a long time for its physiological functions associated to digestion and nutrition. However, in the last few years it has received special attention due to its relevance as a defense mechanism, responsible for its role in supporting the maturation of the immune system. It is also worth highlighting that the GIT is inhabited by a significant number of microorganisms, called microbiota, closely related to the host. 

Figure 1: Gram-positive bacteria have a thick layer of peptidoglycan (PGN), shown in black, outside the membrane. Gram-negative bacteria have significantly less PGN inside the membranes. 

Ways in which the relationship between the microbiota and the immunity of the host in the GI tract may affect poultry performance  

Microbiome is the term used to describe all microorganisms and their genome (viruses, bacteria, mycoplasmas, etc.) that inhabit the gut, the skin or the mucosae of an animal or human. The word microbiota refers to the group of bacteria that inhabit these sites, and they are the most widely studied groups. The functions of these microorganisms are: 

• protective (they compete against each other)

• structural (cell renewal, mucus production and intercellular junction)

• metabolic (producing organic acids and vitamin synthesis)

• immunological (building and inducing immunological tolerance) for the host

Figure 2: Chicken intestinal epithelium: the arrow indicates the normal thickness of the lamina propria (left). Intestinal epithelium with dysbiosis: the arrow indicates the increased thickness of the lamina propria, with infiltration of immune cells and edema (right).

Studies comparing the immune system of conventional and gnotobiotic (germ-free) animals have shown that the lack of microorganisms, or a small number of them, hinder the maturation and the efficacy of the immune system in the presence of pathogens. Thus, having a diverse and balanced microbiota is key for the animal´s health. This microbiota must be recognized by the animal´s innate and acquired immune systems, thus having an effect on its maturation.  

The innate immune system represents the first line of defense, and its receptors (toll like receptors, proteins, peptidoglycan ligands, NOD, etc.) are able to recognize the standard structures in the microorganisms that are not present in the animal cell and generate a defense response, as for example, the structure of the cell wall, which contains lipopolysaccharides and peptidoglycans (PGN). When the receptors recognize these structures, several components are released – including antimicrobial peptides, phospholipases, reactive nitrogen and oxygen species – that tend to destabilize the microorganism, causing its death and facilitating the action of phagocytosis by releasing the complement system. There is also the release of cytokines that trigger a specific immune response against the agent.  

Asian trials show Balancius improves broiler performance

In a trial conducted at the Sri Ramadhootha Poultry Research Farm in Hyderabad, Balancius at 25,000 LSU(F)/kg significantly improved the body weight gain, and feed efficiency in commercial broilers raised in floor pens with litter compared to un-supplemented group (Figure 3).

Figure 3: Balancius improves bodyweight gain and feed conversion at day 35 in broilers.

Sri Ramadhootha Poultry Research Farm, 2018

In an evaluation conducted at the Bangkok Animal Research Center, Balancius also demonstrated improvements in the performance of broilers (Figure 4) which resulted in reduction in feed cost to produce per kilo of broiler (Figure 5). A more marked effect was observed when Balancius was added at 25,000 LSU(F)/kg on top of an antibiotic growth promoter.

Figure 4: Effect of Balancius on broiler performance at day 35.

BARC 2020

Figure 5: Feed cost/kg gain (THB).

BARC 2020

Additionally, the cell wall is made up of PGN or murein, which is an oligomer of sugar and peptides. In the case of Gram+ bacteria, the PGNs make up 90% of the cell wall, and in Gram– bacteria, they make up only 10% of the cell wall. When the PGNs come in contact with the receptors in the animal cell, as NOD, PGLYRP, RegIII3A, mannose binding lectin (MBL) and lysozyme, the process of response induction on the part of the host is initiated. There is the translocation of NF-kβ to the nucleus of the cell, activating several genes of the innate immune response linked to inflammation. The cell wall of bacteria is very dynamic, and it changes constantly throughout its life. The PGNs are small very active parts in the immune system for the inflammation process. Some receptors, as the PGN-recognize proteins, C-type lectin receptors and lysozyme are able to depolarize bacteria and prevent the colonization of the mucosa by microorganisms.

Thus, the fragments generated during the life cycle of the microorganisms, or during the changes of the microbiota in the GIT, may induce chronic inflammation that can affect the functionality of this organ (Figure 2).

The farming system used in industrial poultry production allows for the management of several factors, as the facilities and the nutritional factors that alter the diversity of the microbiota throughout the animal´s life cycle. These changes are responsible for triggering alterations in the microbiota and generating dysbiosis, which affects the bacterial exchange with the possible release of more PGN components. This may alter the status of immunological tolerance and induce the disease process, with its metabolic consequences, resulting in lower zootechnical performance. Thus, being able to recognize the times and the factors leading to dysbiosis is very important to control it and implement a loss prevention program. Most of the information and quality data supplied by the feed mill, together with the data on animal management and well-being on the farm, will help to understand and recognize these processes and avoid future losses. 

Final considerations

The structures of the bacterial cell wall, as the PGNs, are recognized by the innate immune system of the animals and have an impact on their immunity and productivity.

• Several factors on the field may lead to an unbalance of the microbiota and will alter its relationship with the host.

• Intestinal integrity is directly related to the performance and the profitability of poultry.

• The balance of the microbiota and the immune response of the host are key to maintaining optimal intestinal functionality.

• Several factors affect this balance and may induce dysbiosis. Thus, systematically monitoring the GI tract (necropsy and other tests: histology, cytokines and other markers) may pave the way to finding the ideal marker of intestinal health.

• Correct sampling and correlating the information supplied by the feed mill, the farm and the processing plant is the only way to manage the figures and be successful in reaching intestinal stability, profitability for the farmer and sustainability for the planet.

*Dr Rolando Valientes ([email protected]) is Manager, Gut Health (Eubiotics) Greater APAC, DSM Nutritional Products Asia Pacific.

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Based and working in the region.