Beyond viscosity: The prebiotic mechanism of xylanase enzymes in poultry

Whilst non-starch polysaccharide-degrading enzymes have been around for over 35 years, we are still learning about their potential benefits. One area of current interest is the production of xylo-oligosaccharides. This article looks at what we currently know and its potential implications.

Let us start by reminding ourselves what we mean by a prebiotic. The International Scientific Association for Probiotics and Prebiotics (ISAPP) defines prebiotics as “a substrate that is selectively utilized by host microorganisms, conferring a health benefit.”

So, we can think of prebiotics as foods or stimuli that support the success of “beneficial” micro-organisms in the gut of our animals, at the same time suppressing the opportunities for “non-beneficial” micro-organisms to thrive.

When we add enzymes, such as ENZY Carboplus, to combat non-starch polysaccharides (NSP), the resulting breakdown products include fragments of the targeted NSPs referred to as xylo-oligosaccharides (XO). For example, in most cases the NSP here is arabinoxylan, or AX (Figure 1). Figure 1 also indicates the bonds between monomers that are disrupted by β-1,4 xylanase enzymes.

The resulting XOs vary in size and depending upon the region of cleaved bonds, the chain length may be as short as 2 monomers, to as long as 8. This difference in size is termed as the degree of polymerization (DP); this is used to classify the XOs as High DP (longer chains) or LP (shorter chains).

HOW DO XO ACTUALLY HELP?
There has been a lot of work over the last 10 years on modes of action, and much work is still required; but there are two main threads to this work.
1. As fermentation substrates, utilisable by the enteric microbiota
2. As stimulants (“stimbiotics”) to increase microbial activity and ability to use carbohydrates

Trials with commercial livestock have shown the benefits of XOs:
• Feed Conversion Ratio (FCR): Over a range of studies in broilers, FCR improvement is fairly consistent, with an average improvement of around 10%. In some challenge trials (Ren 2024, Cao 2025) FCR improvements are even greater, where the comparison is between a challenged control and addition of XO.

• Bodyweight Gain (BWG) shows less consistent improvements, but slightly higher at 9% – for example, an increase in average daily weight gain from 63 g to 68 g, potentially reducing grow-out period by 2 days.

• There appears to be a beneficial effect on intestinal architecture and integrity. In several trials, villus height increases and crypt depth declines, indicating better potential nutrient absorption with lower energy expenditure on enterocyte replenishment. Additionally, when experiments have looked at gene expression of tight junction proteins, these are often significantly up-regulated, suggesting a more secure intestinal structure.

• Inflammation and oxidative stress might also be improved, with some limited trials showing reductions in markers such as malonaldehyde (MDA), Interleukin 6 (IL-6), and Tumour Necrosis Factor α (TNF-α).

Many of these trials have been conducted with added XO products. These are manufactured from various vegetable materials, and result in products with variable – and usually unmeasured – degree of polymerization. In these studies, the inclusion levels of these products ranged from 0.15 g up to 30 g per kg of feed. This, in turn, resulted in a varied concentration of active xylo-oligosaccharides ranging from 0.019 g to 21 g/kg of feed!

CAN WE APPLY THIS KNOWLEDGE TO ENZYME APPLICATIONS?
If we consider a broiler diet based on wheat and soya, we can calculate the potential XO release by ENZY Carboplus as follows:

This means the potential supply of XO from an effective carbohydrase enzyme like Carboplus can be up to ten times higher than levels used in trials that showed beneficial results.

The answer is therefore, yes: we can apply such knowledge to enzyme applications.

THIS SHINES A LIGHT ON THE BENEFITS SEEN IN MAIZE-BASED DIETS
This concept also answers a fundamental question about NSP-degrading enzymes: why are they still effective when used in a maize-based diet? For all enzymes to be effective, they must have a substrate to work upon; and the level of the substrate is one of the factors that determines the value of an enzyme. The NSP content of maize is a lot lower than that for wheat.

Total NSP content for maize is typically 30% lower than for wheat. Even more striking is the soluble NSP content – over 55% lower. Our understanding of the detrimental effect of NSPs is that a lot of the problem comes from increased viscosity, which is directly related only to the soluble portion. We would therefore expect improvements in performance in maize-based diets to be proportionately less.

However, now that we understand that a significant portion of improvements come from a prebiotic effect, we can begin to appreciate why – even in diets based on maize – we can expect considerably greater improvements in performance, or an appreciable allocation of nutrient sparing capacity.

VARIATION IN XO STRUCTURE
It was previously mentioned that the structure of XO is variable. When the NSP enzyme cleaves the arabinoxylan structure along the xylan “backbone”, it results in fragments that vary in size, from only two xylose molecules linked together up to eight or more. The larger XO are said to have a higher degree of polymerization (DP). Do these differences have an impact on their ability to function as prebiotics?

Research in the field is scarce. Ren et al. (BMC Microbiology,2025) conducted in-vitro trials based on collected broiler caecal contents. This culture medium was then used to test the ability of XO with varying degrees of polymerization to resist the impact of avian pathogenic Escherichia coli (APEC). Bacterial population evenness (Pielou index) was significantly reduced by APEC, whilst application of all XO treatments improved evenness. Diversity was improved by all XO treatments, compared to APEC challenge. The treatment with the highest DP – X4, xylotetraose – enhanced levels of Bifidobacterium very significantly, whilst X3, xylotriose was most effective at increasing butyric acid levels. Both of these factors are associated with “improved” gut environment.

Wallace et al. (Animal Nutrition 2026) used extracts from commercial XO products to produce low DP (X2, X3) and high DP (X4 and above) test materials, fed at 150 g / tonne of feed (Figure 2). When fed to broilers to 35 days of age using a diet based on wheat, barley and sorghum, the results shown in Table 2 were obtained.

Additionally, there were differences in bacterial populations in the ileal digesta and excreta. Here, the low DP containing diet showed a significant increase in Enterobacteriaceae. This is of potential concern, as this large family of Gram-negative bacteria contains the potential pathogens Salmonella and Escherichia coli.

It appears the birds responded more favourably to higher DP XO additions. The authors theorise that this may be due to a “stimbiotic” effect – that is, XO act as signaling molecules, stimulating fibre-degrading microbiota to increase extracellular enzyme production.

SUMMARY AND THE WAY FORWARD
What does all of this mean for our conventional approach of adding NSP-degrading enzymes to broiler diets? In addition to the well-known effects of reducing digesta viscosity and disrupting the “cage effect”, we now see the potential of the break-down products of arabinoxylan disruption to act as stimulators and modulators of hind gut fermentation. In turn, this leads to enhanced performance and – potentially – enhanced protection against pathogens such as APEC, Salmonella and Clostridia.

More work is clearly required to confirm the potential of this approach, and the preferred degree of polymerization of XO. Once this is established, research then needs to be conducted to quantify the XO classifications arising from application of different xylanase products.

About Martin Smith
Scientific Product Manager, Enzymes at Kaesler Nutrition GmbH, Martin Smith is a practicing commercial nutritionist, with extensive knowledge across a wide range of additives and their impact on animal performance, health and welfare.

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