Degradability of alfalfa saponins in the digestive tract of sheep and their rate of accumulation in rumen fluid

Two experiments were conducted to examine the fate of alfalfa saponins in t he digestive tract of sheep. In the first experiment 14.4 or 28.8 g saponin s were administered intraruminally daily, which provided 62 and 78% of the total saponin entering the rumen. Degradabilities of the saponins in the to tal digestive tract were 96.0 and 97.9% (P = 0.13), respectively, but no at tempt was made to determine how closely the products of degradation were re lated to the original molecules. In the second experiment, the rate of rele ase of saponins from alfalfa into rumen fluid was measured in the presence and absence of viable bacteria. When no viable bacteria were present 74% of the saponins in the alfalfa appeared in rumen fluid after 8 h of incubatio n and this amount was unchanged at 24 h. Rate of release did not follow fir st order kinetics, rather an amount equivalent to approximately 8% of the o riginal saponin concentration accumulated in the fluid each hour over the 8 -h period. After 4 h, saponin concentrations in rumen fluid were decreased in the presence of viable bacteria indicating microbial metabolism was occu rring. Final accumulation of saponins in the rumen fluid after 24 h incubat ion was 62% of that originally present in alfalfa samples when viable bacte ria were present. It was concluded that saponins were rapidly released into rumen fluid and extensively degraded in the digestive tract. The implicati ons of these observations on ruminant bloat are discussed.