The Role of Carbohydrates in Urea Utilization, Cellulose Digestion and Fatty Acid Formation

Abstract

Urea utilization by rumen microorganisms in vitro was dependent on the amount and type of carbohydrate used as the energy source. The extent of urea utilization was slightly greater with starch than with cellulose. Xylan and pectin promoted urea utilization but not to the same extent as starch. The distribution and the amount of volatile fatty acids formed were also dependent on the amount and type of carbohydrate used. Total fatty acid production was greatest with starch, followed by dextrose and then cellulose. Comparable levels of starch generally yielded proportionately more acetic, butyric and valeric acids, and less propionic acid than cellulose. Dextrose gave higher percentages of butyric and valeric acids and a lower percentage of acetic acid than starch when used in combination with cellulose. High input levels of dextrose, when used in combination with cellulose, inhibited cellulose digestion markedly. This was accompanied by a marked increase of the relative concentrations of butyric and valeric acids and a reduction in acetic acid. Comparable high input levels of starch up to 1% of the medium in combination with 1% cellulose increased the rate of cellulose digestion and fatty acid formation. High input levels of starch, when used as the sole carbohydrate source, resulted in a marked increase in valeric acid concentration with a corresponding decrease in propionic acid concentration. The data point to different metabolic pathways for the various carbohydrate substrates or a dynamic microbial population changing in number and type with changes in substrate. Copyright © . .