An investigation into the mechanism of action of xylanase in pigs fed insoluble corn-based fiber
Arabinoxylans comprise the majority of the dietary fiber (DF) found in corn and its co-products, and these feed ingredients are commonly used in swine diets. Xylanase is a carbohydrase that hydrolyzes the β-(1-4) glycosidic bonds of arabinoxylan and may improve the utilization of DF. However, its efficacy in corn-based swine diets is quite variable but has shown to reduce finishing pig mortality in commercial settings. The variable efficacy of xylanase in pork production, and its unexpected health benefits, warrant greater understanding of its mechanism(s) of action (MOA). Therefore, the objective of this dissertation was to investigate and elucidate a MOA of xylanase in pigs fed corn-based DF. Research presented in Chapter 2 observed xylanase partially mitigated the antinutritive effect of corn-based DF on performance and dietary energy but appeared to require a longer adaptation time than what is typically reported in the literature. Moreover, it was also found that xylanase improved antioxidant capacity, reduced oxidative stress, and enhanced gut barrier integrity. In Chapter 3, the influence of xylanase on the fermentability, digestibility, and physicochemical properties of corn-based DF was investigated. Xylanase markedly improved the fermentation of DF in the cecum, and increased the production of short chain fatty acids, particularly acetate. However, xylanase did not impact digesta viscosity in the large intestine. Using 16s rRNA sequencing, Chapter 4 investigated the influence of xylanase on ileal digesta and mucosa microbiota, and Chapter 5 characterized its impact on microbial taxa in cecal and colonic contents and mucosa. In the ileum, xylanase modulated beneficial microbial communities that are associated with increased acetate and butyrate production and improved gastrointestinal health. Further supporting the findings from Chapter 2. Within the ileum and large intestine, xylanase upregulated predicted gene counts for enzymes associated with arabinoxylan and arabinoxyloligosaccharides degradation, pentose metabolism, and short chain fatty acid production. Collectively, Chapter 4 and 5 revealed xylanase elicits a MOA improving the fermentation of fiber beyond its inherent action (stimbiotic MOA) and modulates a cross-feeding symbiotic metabolism of certain beneficial microbial communities that are known to confer a health benefit (prebiotic MOA). Chapter 6 investigated the efficacy of xylanase to mitigate the nutrient encapsulation effect of DF in the ileum by evaluating the digestibility of arabinoxylan components, structural topography of corn bran identified in digesta via scanning electron microscopy, and modifications to the chemical spectra of ileal digesta using Fourier-transform infrared spectroscopy. Research presented in Chapter 6 provide in vivo evidence of the notion that xylanase exposes trapped intracellular components to endogenous enzyme within the intestine. The purpose of Chapter 7 was to assess the impact of dietary adaptation time on the efficacy of xylanase in multiple gastrointestinal locations using a dual-cannulated pig model. The findings from Chapter 7 revealed xylanase improves fiber digestibility in the upper small intestine when given sufficient adaptation time (> 25 days). This may partially explain why increased adaption time improved growth performance in Chapter 2. Overall, research presented in this dissertation improved our understanding of the MOA of xylanase in pigs fed corn-based fiber and found increasing adaptation time may improve its efficacy.