Nutritional value and physiological effects of D-xylose and L-arabinose in poultry and pigs

The main sugars other than glucose, which will be released from a hydrolysis of nonstarch polysaccharides, are D-xylose and L-arabinose. The results of studies on the fate of both pentose sugars after oral administration in poultry and pigs are presented. Digestibility of L-arabinose at the end of the ileum was found to be lower than that of D-xylose. The presence of D-xylose or L-arabinose in the diet increased the ileal flow of volatile fatty acids in pigs, suggesting microbial degradation of both sugars in the small intestine. Both pentose sugars were partly excreted in the urine. The extent of this urinary excretion, as a percentage of intake, increased as the dietary inclusion of either of the two sugars was increased. At equal dietary levels, more xylose than arabinose was excreted in the urine. Feeding of D-xylose and L-arabinose to pigs and poultry caused some physiological changes. In chicks these changes resulted in wet droppings. The net energy value of both pentose sugars was calculated to be approximately 25 to 35% of that of D-glucose

Nutritional implications of D-xylose in pigs

Hemicellulose consists primarily of pentose sugars, joined together in a polysaccharide chain with D-xylose as the most abundant component. Ileal digestibility and urinary excretion of D-xylose and associated effects of this pentose sugar on ileal and faecal digestibility of dry matter (DM), organic matter (OM), gross energy (GE) and nitrogen were studied in pigs. Castrated pigs were prepared with a post-valvular T-caecum cannula to measure ileal digestibility. Faecal digestibility was measured in non-cannulated pigs. D-xylose was given at dietary inclusion levels of 100 and 200 g/kg, and the control sugar, D-glucose, at a rate of 200 g/kg diet. Ileal digestibility of D-xylose as well as that of D-glucose was found to be close to 100%. The presence of D-xylose in the diet decreased ileal digesta pH and increased ileal flow of volatile fatty acids, suggesting the occurrence of microbial degradation of D-xylose in the pig small intestine. In pigs fed on the 100 g D-xylose/kg diet, 44.5% of the D-xylose intake appeared in the urine. This percentage increased significantly to 52.6 when pigs were fed on the 200 g D-xylose/kg diet. Ileal and faecal digestibility of DM, OM, GE and N, as well as N retention, decreased significantly in pigs fed on the 200 g D-xylose/kg diet. Chemicals/CAS: Fatty Acids, Volatile; Xylos

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 obtain more information on the role of the intestinal microflora in the anti-nutritive effects of NSP in broiler chicks. As the NSP source, highly methylated citrus pectin (HMC) was used at a dose level of 30 g/kg in a maize-based diet. The diets fed to the germ-free chicks were -irradiated, whereas those fed to the conventional chicks were not. Feeding the HMC diet to conventional birds depressed weight gain and food utilization (P < 0?05), whereas in germ-free birds only weight gain was reduced (P < 0?05). Feeding the HMC diet to conventional birds reduced digestibilities of energy and starch at the end of the jejunum. Ileal digestibilities of starch and energy were not strongly affected when birds were fed on the HMC-containing diet. Faecal 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 affected faecal digestibility of nutrients and N retention, whereas metabolizable energy was increased. Feeding the HMC diet to conventional or germ-free birds increased the viscosity of the digesta in the small intestine. This increase in digesta viscosity was more pronounced in conventional than in germ-free birds. The pH of ileal digesta 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 morphology. Based on the results of the present study, it is concluded that the gastrointestinal microflora mediates the magnitude of the anti-nutritive effects of HMC in broiler chicks. However, the exact role of the microflora in chicks in the magnitude of the anti-nutritional effects of HMC could not be derived from the present study, since the results might have been influenced by -irradiation of the diets fed to the germ-free chicks

Exact results for hydrogen recombination on dust grain surfaces

The recombination of hydrogen in the interstellar medium, taking place on surfaces of microscopic dust grains, is an essential process in the evolution of chemical complexity in interstellar clouds. The H_2 formation process has been studied theoretically, and in recent years also by laboratory experiments. The experimental results were analyzed using a rate equation model. The parameters of the surface, that are relevant to H_2 formation, were obtained and used in order to calculate the recombination rate under interstellar conditions. However, it turned out that due to the microscopic size of the dust grains and the low density of H atoms, the rate equations may not always apply. A master equation approach that provides a good description of the H_2 formation process was proposed. It takes into account both the discrete nature of the H atoms and the fluctuations in the number of atoms on a grain. In this paper we present a comprehensive analysis of the H_2 formation process, under steady state conditions, using an exact solution of the master equation. This solution provides an exact result for the hydrogen recombination rate and its dependence on the flux, the surface temperature and the grain size. The results are compared with those obtained from the rate equations. The relevant length scales in the problem are identified and the parameter space is divided into two domains. One domain, characterized by first order kinetics, exhibits high efficiency of H_2 formation. In the other domain, characterized by second order kinetics, the efficiency of H_2 formation is low. In each of these domains we identify the range of parameters in which, the rate equations do not account correctly for the recombination rate. and the master equation is needed.Comment: 23 pages + 8 figure