Does release of encapsulated nutrients have an important role in the efficacy of xylanase in broilers?

The non-starch polysaccharides (NSPs) in cell walls can act as a barrier for digestion of in- tracellular nutrients. This effect is called “cage effect.” Part of the success of fibrolytic enzymes in broiler feed is assumed to be attributed to cage effect reduction. Further, changes in viscosity and potential prebiotic ac- tion should also be considered. The aim of this study was to gain insight into the relative importance of the cage effect in xylanase efficacy in broilers. Using a 2 × 2 factorial design, 24 pens with 30 Ross 308 male chicks were fed corn-soy based diets consisting of nor- mal and freeze-thawed (5 d at -18◦C) corn, both with and without xylanase. The freeze-thaw method was used to eliminate the cage effect, whereas a corn-based diet was used to exclude viscosity effects. Body weights (BW), feed intake (FI), and feed conversion ratio (FCR) were determined at d 13, 26, and 39. A balance study was executed at the end of the growing phase. These birds were euthanized at d 34 (non-fasted) to determine the viscosity of digesta, blood metabolites, intestinal morphology, and microbiota composition. During the finisher period, there was a significant interaction be- tween enzyme supplementation and freeze-thawing for FCR, in which FCR was improved by freeze-thawed corn and tended to be improved by normal corn + en- zyme compared with the control group. The improve- ment in performance (finisher period) of freeze-thawed corn and xylanase coincided with increased gut absorp- tion of glucose (based on postprandial plasma concen- trations) and increased number of Clostridium cluster IV in the caecum, and agreed with the higher gut vil- lus height. In addition, xylanase inclusion significantly increased the postprandial plasma glycine and triglyc- erides concentration, and led to elevated bacterial gene copies of butyryl CoA:acetate CoA-transferase, sug- gesting a prebiotic effect of xylanase addition through more than just the cage effect reduction. The applied model managed to rule out viscosity by using corn, and it was possible to isolate the cage effect by freeze- thawing the dietary corn.