Observations on the fermentation of carbohydrates along the gastro-intestinal tract of a fistulated cow.

Abstract

One cow was provided with cannulae in the proximal duodenum and terminal ileum. Three experimental rations were offered: 1, hay 7 kg/day and concentrate 6; 2, hay 3 kg/day, paper pulp 3 and concentrate 3.7; 3, fresh grass 11 kg DM/day. Rations 2 and 2 were given twice daily and 3 was offered more frequently. Experimental periods were 5 days in experiment 1 and 7 days in 2 and 3. Samples were taken from each cannula every 2 h for 5 days. Faeces were collected in each period. Flow rate of the intestinal contents was measured with polyethylene glycol and chromium sesquioxide as markers. Carbohydrates in the feed, digesta and faeces were fractionated according to solubility into ethanol-soluble sugars, alpha -glucose polymers, fructosan, water-soluble polysaccharides other than alpha -glucose polymers and fructosan, neutral-detergent-soluble polysaccharides and neutral-detergent residue. Sugars, sialic and uronic acids were measured in the hydrolysates and the sugars were separated chromatographically.Most of the ethanol-soluble sugars and all the fructosan was digested in the rumen, reticulum, omasum and abomasum, considered collectively as the stomach. Digestion of alpha -glucose polymer occurred mainly in the stomach and only 5 to 10% was digested in the small intestine and caecum with colon. The hay and concentrate ration contained more starch than the others and a higher proportion of this was digested in the small intestine and caecum with colon (20.3 and 6.8% of the digestible starch). The water-soluble fraction was digested mostly in the stomach; on rations 1 and 3 more component carbohydrates disappeared from the small intestine than the caecum with colon. Bacterial polysaccharides were thought to be digested in the small intestine and some bacterial growth was indicated, particularly on ration 2 which contained large amounts of cellulose. Fermentation and addition of bacterial polysaccharides and mucus confused the picture of digestion of the neutral-detergent-soluble fraction, but on all 3 rations it was higher in the small intestine than in the caecum with colon. The neutral-detergent residue was mainly fermented in the stomach and the caecum with colon. (Abstract retrieved from CAB Abstracts by CABI’s permission)