RUMINAL AND FECAL FATTY ACIDS AND APPARENT RATION DIGESTIBILITY IN LAMBS AS AFFECTED BY DIETARY FATTY ACIDS

Abstract

Two metabolism experiments were conducted with rumen-fistulated sheep to study effects of increasing dietary levels of unsaturated fatty acids upon ration digestibility and rumen-fluid volatile fatty acids. Apparent digestibility of ration components was not significantly (P > 0.05) affected by diet. However, crude fat digestibility values, which include fecal soap excretion, were 11–19 digestion units lower than comparable ether extract values. When diets high in unsaturated fatty acids were fed, the rumen and fecal levels of these acids were lower than dietary levels, suggesting that hydrogenation of C-18 polyethnoid fatty acids was occurring. Fecal soap excretion was affected very little by dietary unsaturated fatty acids, but stearic acid proportion of fecal soaps increased as the level of dietary unsaturated fatty acids increased. The ratios of acetic to propionic acid gradually decreased as the unsaturated fatty acids of the ration increased in one experiment, but in the other experiment no consistent pattern was observed.