Effect of viscosity on digestion of nutrients in conventional and germ-free chicks

A study was conducted with conventional and germ-free broiler chicks to obt ain more information on the role of the intestinal microflora in the anti-n utritive effects of NSP in broiler chicks. As the NSP source, highly methyl ated citrus pectin (HMC) was used at a dose level of 30 g/kg in a maize-bas ed diet. The diets fed to the germ-free chicks were gamma-irradiated, where as those fed to the conventional chicks were not. Feeding the HMC diet to c onventional birds depressed weight gain and food utilization (P < 0.05), wh ereas in germ-free birds only weight gain was reduced (P < 0.05). Feeding t he HMC diet to conventional birds reduced digestibilities of energy and sta rch at the end of the jejunum. Ileal digestibilities of starch and energy w ere not strongly affected when birds were fed on the HMC-containing diet. F aecal digestibilities of organic matter, crude fat, starch and amino acids, N retention and metabolizable energy were reduced when conventional chicks were fed on the HMC diet. Feeding the HMC diet to germ-free birds hardly a ffected faecal digestibility of nutrients and N retention, whereas metaboli zable energy was increased. Feeding the HMC diet to conventional or germ-fr ee birds increased the viscosity of the digesta in the small intestine. Thi s increase in digesta viscosity was more pronounced in conventional than in germ-free birds. The pH of ileal digests was reduced when HMC was added to the diet of conventional chicks, but not in germ-free chicks. Feeding the HMC diet to conventional birds markedly affected morphology of the gut wall , whereas in germ-free chicks very little effect was found on gut morpholog y. Based on the results of the present study, it is concluded that the gast rointestinal microflora mediates the magnitude of the anti-nutritive effect s of HMC in broiler chicks. However, the exact role of the microflora in ch icks in the magnitude of the anti-nutritional effects of HMC could not be d erived from the present study, since the results might have been influenced by gamma-irradiation of the diets fed to the germ-free chicks.