Xylose: absorption, fermentation, and post-absorptive metabolism in the pig

Abstract

Xylose, as β-1,4-linked xylan, makes up much of the hemicellulose in cell walls of cereal carbohydrates fed to pigs. As inclusion of fibrous ingredients in swine diets continues to increase, supplementation of carbohydrases, such as xylanase, is of interest. However, much progress is warranted to achieve consistent enzyme efficacy, including an improved understanding of the utilization and energetic contribution of xylanase hydrolysis product (i.e. xylooligosaccharides or monomeric xylose). This review examines reports on xylose absorption and metabolism in the pig and identifies gaps in this knowledge that are essential to understanding the value of carbohydrase hydrolysis products in the nutrition of the pig. Xylose research in pigs was first reported in 1954, with only sporadic contributions since. Therefore, this review also discusses relevant xylose research in other monogastric species, including humans. In both pigs and poultry, increasing purified D-xylose inclusion generally results in linear decreases in performance, efficiency, and diet digestibility. However, supplementation levels studied thus far have ranged from 5% to 40%, while theoretical xylose release due to xylanase supplementation would be less than 4%. More than 95% of ingested D-xylose disappears before the terminal ileum but mechanisms of absorption have yet to be fully elucidated. Some data support the hypothesis that mechanisms exist to handle low xylose concentrations but become overwhelmed as luminal concentrations increase. Very little is known about xylose metabolic utilization in vertebrates but it is well recognized that a large proportion of dietary xylose appears in the urine and significantly decreases the metabolizable energy available from the diet. Nevertheless, evidence of labeled D-xylose-1-14 C appearing as expired 14 CO 2 in both humans and guinea pigs suggests that there is potential, although small, for xylose oxidation. It is yet to be determined if pigs develop increased xylose metabolic capacity with increased adaptation time to diets supplemented with xylose or xylanase. Overall, xylose appears to be poorly utilized by the pig, but it is important to consider that only one study has been reported which supplemented D-xylose dietary concentrations lower than 5%. Thus, more comprehensive studies testing xylose metabolic effects at dietary concentrations more relevant to swine nutrition are warranted.

Genome-scale metabolic reconstructions of multiple Salmonella strains reveal serovar-specific metabolic traits

“…They were found to lose the capability to utilize l -arginine as a sole carbon source under anaerobic conditions due to the absence of the succinylglutamic semialdehyde dehydrogenase ( astD ) and l -xylulose in both aerobic and anaerobic conditions due to the absence of three genes ( yiaMNO ). l -xylose is an upstream precursor of l -xylulose and is abundant in the hemicellulose walls of the cereals fed to pigs 21 . It was shown to be excreted in high proportions in the urine indicating very low levels of xylose absorption 21 .…”

“…l -xylose is an upstream precursor of l -xylulose and is abundant in the hemicellulose walls of the cereals fed to pigs 21 . It was shown to be excreted in high proportions in the urine indicating very low levels of xylose absorption 21 . The loss of yiaMNO may have occurred because l -xylulose is not available in the swine extraintestinal environment.…”

“…Indeed, a total of 21 catabolic pathways uniquely contributed to Salmonella fitness during intestinal infection of pigs, cattle, and chickens, including those for the utilization of d -tagatose, l -xylulose, d -xylose, deoxy- d -ribose, l -idonate, d -glyceraldehyde, and allantoin. These metabolites form part of the host’s diet and/or have been observed in the intestinal environment 21 , 44 , 45 . Additionally, we observed that the corresponding catabolic capabilities were missing across strains adapted to either cold-blooded hosts, to swine, or to humans, providing evidence of an isolate’s genotype being influenced by the environment it evolves in.…”

Effects of dietary fibre level and body weight of pigs on nutrient digestibility and available energy in high‐fibre diet based on wheat bran or sunflower meal

“…According to the results of digestibility and energy value, it needs to be further explained that the nutrient digestibility and the ME values are not completely related. Fermentation of DF is a less efficient means to release dietary energy to pigs compared with direct absorption and oxidation of starch, fat and protein (Huntley & Patience, 2018). Noblet and van Milgen (2004) reported that energetic efficiency ofDF (60%) is lower than that TA B L E 8 Effect of sunflower meal (SFM) and body weight (BW) of pig on the digestible energy (DE), metabolizable energy (ME) and the apparent total tract digestibility (ATTD) of nutrients in Exp.…”

Safety of xylo‐oligosaccharides (XOS) as a novel food pursuant to Regulation (EU) 2015/2283

“…In a study with volunteers, 70% of the dose was absorbed (Craig and Ehrenpreis, 1999). A part of D-xylose also reaches the colon, where it is metabolised by gut bacteria (Huntley and Patience, 2018). After intravenous infusion of 20 g 14 C-xylose to one human, 13.5% of the dose was detected in expired CO 2 .…”