Roles of fibre fermentation in monogastric animals: β-1,4-endo-xylanase increases total VFA and butyric acid production in broiler ceca
Increasing post-ileal fibre fermentation in monogastric animals creates a number of beneficial effects such as increased nutritive value of feedstuffs and augmented intestinal barrier function. Intestinal barrier function is largely influenced by composition and healthiness of commensal microflora relative to potentially pathogenic microflora. In this respect the role of xylanase on increasing post-ileal fibre fermentation shouldn't be undervalued. As there is increasing interest in feeding animals for their microbiota, a series of AB Vista Research Highlights in this financial year will be focused on intestinal fibre fermentation in relation to the roles of fibre fermentation end-products and their impacts on microbial composition in mono-gastric animals. The main paper introduced in this first version is the paper published by Masey-O'Neill et al. (2014) (Effect of exogenous xylanase on performance, nutrient digestibility, volatile fatty acid production and digestive tract thermal profiles of broilers fed on wheat- or maize-based diet. British Poultry Science 55, 351-359).
Increasing post-ileal fibre fermentation leads to an increased energy extraction from feeds consumed by animals as fibre fermentation by-products (volatile fatty acids or VFA) are rapidly absorbed and contribute to the whole-body energy pool. Moreover, fibre fermentation VFA production leads to a stronger barrier function as (1) increased VFA production competitively reduces the production of nitrogen fermentation by-products which are irritants to enterocytes, and (2) increases butyric acid production which is an important energy source for enterocytes and their proliferation. However, a number of recent studies suggest that fermentation of fibre and production of beneficial VFA are dependent on the type of fibre entering ceca and large intestine and adaptation/maturation of intestinal microbiota.
In this study Masey-O'Neill et al. (2014) fed either corn- or wheat-base diet without and with β-1,4-endo-xylanase (Econase XT, EXT, AB Vista) to broilers for 49 days. At the end of 49-day experiment, birds were euthanised and VFA concentration in the ceca was measured (Figure 1). Results showed that microbiota in the ceca ferment wheat fibre better than corn fibre (P<0.001) and supplementation of xylanase significantly improves fermentation of fibre and hence produces greater amounts of total VFA (P<0.001) and butyric acid (P<0.001) regardless of cereal sources. This finding supports previous finding that short-chain xylo-oligomers are significantly increased at the end of ileum of birds fed wheat-based diet with xylanase (Apajalahti and Bedford, 1998. Western Nutrition Conference), which is the source of increased VFA production by post-ileal commensal microbiota.
Figure 1. Caecal concentration of volatile fatty acids (VFA) at 49 days of age in broilers fed either corn- or wheat-based diet without/with xylanase (Econase XT). Both cereal grain (P<0.001) and xylanase (P<0.001) had significant effect on total VFA and butyric acid concentrations. Masey-O'Neill et al., 2014.
Figure 2. Effect of cereal type and xylanase (Econase XT) on feed conversion ratio in broilers. For the first 28 days type of cereal had a significant effect (P<0.01) while xylanase had no effect (P>0.10), but overall for 49 days the cereal effect diminished (P>0.10) while xylanase significantly improved FCR (P<0.001). Masey-O'Neill et al., 2014.
Unfortunately, this study did not measure VFA production at early stage of life when post-ileal commensal microbiota are not fully developed for fibre fermentation. However, the authors measured nutrient digestibility and performance response at days 28 and 49. As presented in Figure 2, supplementation of xylanase did not improve FCR at day 28 but did improve FCR over the entire 49-day trial (P<0.001). Moreover, at day 28 xylanase supplementation improved ileal digestibility of dry matter and nitrogen in both corn- and wheat-based diets while, ileal energy digestibility was improved only in the wheat-based diet. In contrast, at day 49 xylanase supplementation improved ileal energy digestibility in both wheat- and corn-based diets, indicating age-dependent differences in fibre fermentation capacity of broilers.
In conclusion, the findings of this paper suggest that xylanase supplementation improves fibre fermentation in birds, however, intestinal microbiota need time to adapt to efficiently ferment the short-chain fibers produced by xylanase in both corn- and wheat-based diets.