Carbohydrate metabolism in the ruminant

Abstract

1. Samples of mixed bacteria were separated from rumen digesta taken from calves, kept out of contact with adult animals, and from sheep and cows.2. For calves receiving a diet made up of equal amounts of roughage and cereals with 13–16 g nitrogen/kg dry matter, samples of mixed bacteria taken 4–6 h after feeding contained, on average, 140 g glucose in α-linked polymers (α-dextran), 25 g galactose and a total of 25 g other non-glucose, non-galactose sugars (mainly rhamnose, ribose and mannose) in combined forms per kg dry matter.3. The α-dextran content of similar bacteria samples from sheep or cows receiving diets of similar composition was 70 g/kg dry matter. Samples from animals receiving all-roughage diets contained only 25 g α-dextran/kg dry matter, but those from cows given more than 70% of their ration as concentrates (mainly cereal) contained 150 g α-dextran/kg dry matter.4. Addition of supplementary protein or urea to cereal–roughage diets given to calves greatly depressed the amount of α-dextran in the rumen bacterial samples to an average value of 60 g/kg dry matter.5. Samples taken before a morning feed (i.e. after 16 h fasting) contained less α-dextran than samples taken 4–6 h after feeding for both calves and cows.6. Under different conditions, variations in the amounts of galactose in rumen bacteria sometimes paralleled variations in α-dextran. Amounts of other non-glucose sugars did not vary greatly.7. It was estimated, from a comparison of the compositions of rumen bacteria and duodenal contents, that, in the latter, the rhamnose, ribose and mannose came mainly from the bacteria, the arabinose, xylose and cellulose-glucose mainly from the diet and the galactose and α-dextran-glucose from both sources.