In general, poultry is incapable of utilising substantial amounts of energy from fermentation processes that occur in their hindgut. Nevertheless, controlling fermentation in the gut and regulating the bacterial population responsible for it, is gaining interest. Therefore, dietary fibre and prebiotics are now considered promising feed components again.
By Ronny Mombaerts and Kurt Van De Mierop, Nutrex nv, Lille, Belgium
Prebiotics are carbohydrate structures that resist digestion and absorption in the small intestine, but that are partially or completely fermented in the hind gut. This selective fermentation can change the activity and composition of the intestinal flora leading to increased production of short chain fatty acids (SCFA) and a suppression of protein fermentation. Reduced protein fermentation is desired because it results in the creation of potentially toxic metabolites such as ammonia, other amines, phenols, indoles, etc. This shift in microbiota may also result into macro-effects such as an increased resistance against pathogens and improved performance.
So far, inuline or inuline-derived oligosaccharides are the market leaders in this field and are widely used in the food industry as bifidogenic factors. Besides inuline, several other molecules receive interest. Since arabinoxylans are abundantly present in dietary fibre of most cereals, this could be a very interesting alternative.
In the past, considerable efforts were made to optimise the production methods of AXOS. Enzymatic degradation of native arabinoxylans (AX) from cereals into AXOS could be an interesting production process and can be achieved in vitro by incubating de-starched and deproteinised wheat bran with Bacillus subtillus xylanase (Swennen et al., 2006). This xylanase converts a fraction of AX from wheat bran into AXOS. After characterisation of the enzymatically derived AXOS from wheat bran, the effect of dietary inclusion at different dosage on growth and feed conversion in broilers was assessed.
In the trial, a corn-soy diet was used and feed conversion improved by adding AXOS (Figure 1). The bacterial enzyme preparation had a similar effect compared to the best AXOS group, but was for unknown reasons underdosed at only 20% of the recommended level in practice.
Van Craeyveld et al. (2008) investigated the effects of orally supplemented AXOS on fermentation metabolites in the caecum and colon of rats. The researchers concluded that AXOS with an average degree of polymerisation of 5 and an average degree of arabinose substitution of 0.27 (AXOS 5-0.27) exhibited the best combination of desirable effects on gut health characteristics. Addition of AXOS 5- 0.27 to the diet resulted in increased acetate and butyrate levels, reduced ammonium and branched SCFA concentrations and a higher bifidobacteria count in the caecum. These are indications of increased carbohydrate fermentation and reduced protein fermentation.
Feed enzyme bacterial endo-xylanase
Looking at the diet composition of monogastric animals in practice, AX levels are around 6 and 5 % resp. for wheat and corn based diets, with a majority being insoluble in both diet types. Bacterial endo-xylanase (Nutrase Xyla, Bacillus subtilis endo-β -1,4-xylanase, Nutrex nv, Belgium) offers a greater potential to create AXOS than fungal xylanase. Firstly, because the optimal working pH corresponds to intestinal pH conditions, where residence is longer compared to stomach or gizzard, and secondly due to large superiority in degradation of insoluble AX, which is the majority of the AX fraction (Courtin, 2001). Manfredo (2011) showed that adding Nutrase Xyla to a corn based broiler trial had a very large impact on intestinal flora. Firmicutes, known for their antiinflammatory action and butyrate production, increased while bacteroides numbers (which are protein fermenters) reduced.
In vivo effect in corn-soy diets
Many nutritionists are still convinced that use of xylanases provides little or no benefit in corn-soy diets, due to the low levels of soluble NSP's in such diets, which they consequently consider to have little anti-nutrional value in terms of NSP. The effect of the unique properties of a bacterial endo-xylanase in corn-soy diets is demonstrated in two trials described below.
The first study (Figure 2) was undertaken to verify the response of Nutrase Xyla and two other commercial NSP products, each at commercial dosage, using US broiler production conditions and raw materials. Enzyme F is a multienzyme which includes fungal xylanase and -glucanase as principal enzyme activities, Enzyme M is a mannanase.
The positive control diets (Feed 1) were formulated to be similar to commercial industry standards and did not include NSP-enzymes. Negative control and enzyme supplemented diets (Feed 2) were formulated to be lower in metabolic energy (100 kcal/kg) and digestible amino acids (2%), which resulted in a 4% cost reduction of the feed at the time of the trial. Reduction of energy, digestible amino acids and cost was achieved by inclusion of cereal by-products to replace corn and soybean meal.
Besides overcoming the reduced nutrient levels and achieving near identical performance to the positive control group, Nutrase Xyla was also the only enzyme that significantly reduced mortality to 2.38% compared to 6.19% in the positive control group.
The second trial (Figure 3) set up to compare the effect of Nutrase Xyla to the same Enzyme F, each at commercial dosage, on the performance of fattening pigs from 20 to 110kg. Feed 1 was formulated to be similar to commercial industry standards. Feed 2 was lowered 40 kcal/kg in Net Energy without affecting the amino acid profile. Energy reduction was accomplished by reducing the fat content or replacing corn by cheaper wheat byproducts. Both trials showed clear advantages of using the bacterial endo-xylanase on animal performance in corn-soy diets.
These findings confirm that the role of NSP enzymes is not limited to viscosity reduction or liberation of nutrients, but can also impact on intestinal health by creating prebiotic substances. This implies that enzyme efficacy in the field (challenged gut) does not completely correspond with enzyme efficacy in research units, enzymes can be useful even when anti-nutritional effects of NSP's seem limited, and that extra effects on gut health need be considered when selecting enzyme preparations.
A list of references are available on request from the corresponding author. Email: firstname.lastname@example.org
[Source: Enzyme special]