Identifying biomarkers for poultry intestinal health

A simple-to-use tool would help in the assessment of gut health. There are numerous markers that could be used as an indication of gut health, allowing treatments to be more targeted.

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The challenge is to identify which of the numerous biomarkers are predictive for health, said Ghent University Professor Filip Van Van Immerseel. (Mark Clements)
The challenge is to identify which of the numerous biomarkers are predictive for health, said Ghent University Professor Filip Van Van Immerseel. (Mark Clements)

Measuring gut health on farm should be possible using simple tools within the next few years, and various biological markers could be used to indicate the state of a bird’s gut health, according to Filip Van Immerseel, professor at Ghent University, Belgium.

While the challenges of poultry health may be different from those of human medicine, there is quite a lot that a lot that can be drawn from the human field, Immerseel said at the Sixth International Conference on Poultry Intestinal Health (IHSIG).

Take, for example, calprotectin, a biomarker for high levels of gut inflammation in humans. Yet in those cases where symptoms may comprise diarrhea or constipation, there would appear to be little difference in calprotectin levels in challenged and non-challenged individuals, meaning that, in these cases, different information is needed.

A similar situation arises in poultry. When problems are more subtle, for example, inflammation and some dysbiosis, markers associated with severe inflammation will not be evident, but production losses will still occur.

Low-level inflammation may be due to a variety of factors, including mycotoxins, clostridial toxins or diet composition. There are a lot of different possible biomarkers, and the challenge is to identify which are predictive for health challenges.

When disease is severe, microscopic examination and gut health scoring can be used. However, this approach can be somewhat subjective, and influenced by the person conducting the scoring. What is needed is an easy-to-use tool, one into which a sample could simply be placed and a value returned.

Indicators of change

In a healthy bird, there is no reaction to gut lumen bacteria but, should a breach occur, when epithelial cells are dying, or there are endotoxins, mycotoxins, or even coccidia, some bacteria will pass through lesions, triggering inflammation. With inflammation comes a bacterial shift, with some bacterial populations going up and some down.

This change is highly specific and, when looking for biomarkers, there are a lot of different technologies that can identify the various proteins and molecules associated with microbial population shifts, bacterial functionalities and host molecules that end up in fecal material.

With these shifts, the difference in sequences of families, gena, and species can be considered, as can differing functional genes.

Where metabolites are concerned, Immerseel said they will change as the microbial population changes. What is important is to identify those that are linked to dysbiosis and which can also be measured.

Human data sets, again, reveal which bacteria are doing what. There are butyrate producers, which are anti-inflammatory, and others that are inflammatory.

Gut Bacterial Population 2

Changes in bacterial populations in the gut will result in changing biomarkers in fecal matter. (image_jungle | iStock)

Studies have shown that birds with a reduced microbiota are more affected by challenges than those with an intact microbial population. This higher diversity translates into a higher body weight, and is also something that could be measured.

Bacterial families that produce a lot of butyric acid can be depleted when a challenge occurs and, in human intestinal health, there is a strong connection with depletion of these families.

Quantifying these populations would provide something to work with, and using polymerase chain reaction applied to fecal samples and measuring the abundance of these families would be fairly easy to do.

If the potential of bacteria to produce butyrate, hydrogen sulfide or ammonia in a quantitative way could be measured, a good idea of intestinal health could be gained.

There are also host responses that can be considered.

Molecules and proteins from dead epithelial cells, along with proteins that leak out from plasma, will end up in the feces. There are a lot of host proteins that end up in fecal matter, however, it will only be possible to find them if they have not been broken down by proteases.

Gut protectin, for example, is a biomarker in humans that is very distinctive, but while this may be relatively straightforward in humans, it becomes more complicated in chickens.

There are, however, similar proteins that have been found during necrotic enteritis challenges that could be used as a biomarker and that could be identified via enzyme-linked immunosorbent assay. Similarly, there are proteins that are depleted in challenged animals.

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