May, Katherine
(2017)
Mechanisms of action of xylanase and its commercial application in pig diets.
PhD thesis, University of Nottingham.
Abstract
Xylanase is an exogenous enzyme that is added to non-ruminants diets in order to break down and ameliorate the effects that non-starch polysaccharides (NSPs) have on feed digestibility. Dietary supplementary xylanase reduces viscosity of the digesta to improve feed digestibility and growth performance. Recently a study in broiler chickens (Singh et al., 2012) showed a significant increase in circulating serum peptide-YY (PYY) concentration (p<0.001) in response to xylanase supplementation. PYY is a satiety hormone that inhibits gastric motility, increasing digesta retention times in non-ruminants which has also been identified to occur in studies where xylanase has been supplemented. It is thought this could potentially be another mechanism by which xylanase exerts its beneficial effects on growth outcomes. Therefore the aim of the current study was to explore the effects that xylanase (16,000 BXU/kg diet, Econase XT, AB Vista, UK) supplementation, of a wheat-based feed, has on growth performance parameters and gut/metabolic hormones that are produced from the gastrointestinal tract in pigs, and if age at supplementation affects the efficacy of the enzyme.
In a preliminary trial a human multiplex assay (Human Metabolic Hormone Milliplex HMHMAG34k kit, Merck Millipore, Billerica, MA, USA) was successfully used to measure porcine gut/metabolic hormones simultaneously, and the assay was hence used in subsequent trials. In the same trial it was determined that animals subjected to commercial slaughter (S), which had an increased time to tissue sample collection (approximately 18 hours) and exposes carcasses to a 60°C water bath, did not affect the quality of RNA extracted from gut, pancreatic and liver tissue and subsequent relative abundance of gene transcripts over animals not subjected to this slaughter method (NS).
In two trials on weaned piglets, it was found that dietary xylanase supplementation at 0-2 weeks post-wean decreased glucose-dependent insulinotrophic peptide (GIP), glucagon like peptide-1 (GLP-1) and pancreatic polypeptide (PP) plasma concentrations (p<0.05) which resulted in a tendency for insulin and C-peptide (p<0.08) to be decreased in these animals when bloods were analysed at 6 weeks post-wean. Also at this time point PYY concentrations were found to be decreased (p<0.01) in animals fed diets supplemented with xylanase between 2 and 6 weeks post-wean. In a third trial, when blood parameters were measured at 13 weeks post-wean, leptin and ghrelin levels were higher in animals provided with the exogenous enzyme, supplemented feed at 0-2 weeks post-wean.
In conclusion, it was found growth performance in pigs fed a wheat-based diet supplemented with xylanase was not significantly improved at any age. However timing and/or duration of supplementation affected production of certain gut/metabolic hormones, in particular those produced in the pancreas or those that influence production of these hormones, suggesting dietary xylanase supplementation fed to weaned pigs may affect pancreas function and development.
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