Metabolic fates of U-¹⁴C-labelled monosaccharides and an enzyme-treated cell-wall substrate in the fowl

Abstract

A major benefit of supplementing non-ruminant feedstuffs with exogenous enzymes is presumed to be the degradation of plant cell-wall polysaccharides to metabolizable monosaccharide residues. In the present study, metabolic fates of (U-'4C-labelled, 10 mM) glucose, galactose, mannose, xylose and arabinose were compared in the fowl, by measuring recoveries of 14C radioactivity in exhaled carbon dioxide, excreta and body tissues after administration either by wing vein (iv) or into the crop (ic). A further comparison was made with a tube-fed, enzyme-treated, U-'4C-labelled cell-wall substrate, Festuca avundinacea, and a final experiment tested possible competition for absorption between different cell-wall residues. Delays between iv and ic treatments in recovery of 14C in CO,, which were assumed to reflect intestinal absorption, indicated that xylose was absorbed more slowly than glucose and galactose, but faster than mannose and arabinose. Total recoveries of 14C in CO, and excreta over the whole test period indicated that metabolizabilities were highest with glucose, galactose and mannose, and lowest with arabinose. After testing, 14C recovery in caecal contents was highest with ic arabinose, and recoveries in body tissues, with all sugar treatments, were in the order liver > breast and leg muscle > abdominal fat > plasma. Results with the Festuca substrate showed similar patterns of recovery in body tissues and confirmed an increase in metabolizability with addition of enzymes. The timing of the 14C02 response with Festuca and a wet enzyme pretreatment was broadly similar to a 'predicted Festuca' response, based on the composition of the substrate and the measured responses with individual (ic) monosaccharides. There was no evidence of any competition for absorption or metabolism among cellwall residues. It was concluded that glucose release from cellulose is potentially the most important product of cell-wall degradation to contribute to enzyme enhancement of metabolizable energy.Cell-wall degradation : Monosaccharide metabolism : Enzyme supplementation : FowlIn recent experiments reported elsewhere (Savory, 1992), effects of exogenous enzyme supplementation on degradation of plant cell walls to metabolizable monosaccharide residues were assessed in vivo in domestic fowls. This was done by tube-feeding birds U-'"C-labelled cell-wall substrates, with and without various enzyme treatments, and monitoring recovery of 14C radioactivity in exhaled CO, and excreta in the following 8 h. On average, about 19-61 % of the total 14C activity that was tube-fed, depending on substrate and treatment, remained unaccounted for at the end of the 8 h test period. It was suggested that some of this activity could still have been in contents of the hind-gut but that most was probably in body tissues.To determine metabolic fates of enzyme-degraded cell-wall residues in more detail, further similar trials in the present study were conducted in which measurements were made of I4C activity in contents of the hind-gut and body tissues...

Mistletoebirds and Xylose: Australian Frugivores Differ in Their Handling of Dietary Sugars

“…In chickens, Savory (1992) reported that d-xylose was absorbed slower than d-glucose and d-galactose but faster than d-arabinose and d-mannose, which concurs with results previously reported in chicks (Wagh and Waibel 1967), rats (Kohn et al 1965), and humans (Wood and Cahill 1963), suggesting that the absorption rates of these sugars may depend on their relative contributions of active and passive (transcellular and paracellular) transfer mechanisms (Savory 1992).…”

Enzyme supplementation, degradation and metabolism of three U-14C-labelled cell-wall substrates in the fowl

“…The findings in Fig. 3 suggest that some of this activity could still have been in contents of the hind-gut, but presumably most was in body tissues (recoveries of 14C from these sites were measured in other trials with U-14C-labelled cell-wall material reported elsewhere, Savory, 1992). The differences between dry and wet treatments in percentages of 14C recovered in excreta were almost entirely accounted for by differences in '*CO, production with spinach and Festuca, but not with cellulose (Table 4).…”

“…None of the evidence thus obtained refutes the original assumption (p. 91) that '*CO, production can be used as an indicator of degradation and metabolism of U-'4C-labelled cell-wall substrates. In subsequent trials (Savory, 1992) the model was refined by using three bottles of CO, trapping solution instead of two, and by having nine collection periods, of either 50 or 60 min, instead of eight. With [U-'*C]cellulose the significant reduction in total 14C recovery in exhaled CO, with the antibiotic pretreatment, compared with the no-enzyme, dry control treatment (Table 3), appears to confirm that degradation of cellulose by intestinal microflora does occur…”

Composition, properties, and nutritive value of dietary fibre of legume seeds. A review

“…The increase in the metabolizable energy was not due to complete hydrolysis of NSP by exogenous enzymes and subsequent absorption of the released sugars, but due to the significant increase in apparent pentosan digestibility (26 vs. 44%) and in ileal starch digestibility (88 vs. 98%). A potential contribution of the main cell-wall residues released by feed enzymes to the metabolizable energy in the fowl appear to be in the order: glucose > galactose > xylose > arabinose > galacturonic acid (Savory, 1992).…”