RELATIONSHIPS BETWEEN RUMINANT BLOAT AND THE COMPOSITION OF ALFALFA HERBAGE. II. SAPONINS

Abstract

Although herbage proteins are generally recognized as foaming agents in pasture bloat, a possible secondary role for saponins has not been ruled out. The role of saponins in pasture bloat was re-examined by feeding rumen-fistulated cattle fresh herbage from high saponin (HS) and low saponin (LS) near-isogenic strains of alfalfa. Each alfalfa strain was fed to six animals for 100 days. Feeds from the two alfalfa strains differed significantly in saponin concentration but were equal in protein concentration. At 1.5–2 h after feeding, the cattle were examined for the occurrence of frothy rumen ingesta and for bloat. The HS alfalfa produced 86 instances of frothy rumen ingesta and 50 cases of bloat. The LS alfalfa produced 103 instances of frothy rumen ingesta and 61 bloat cases. There were no significant differences (P > 0.1) between HS and LS alfalfa in the occurrence of bloat or of frothy rumen contents. Generally, saponin concentrations in rumen fluid were below detectable levels and below the estimated level of toxicity to the animals. In view of these results and other strong evidence opposing the saponin theory of pasture bloat, we conclude that saponins do not contribute to the occurrence of alfalfa pasture bloat by either the toxic or the foaming modes of action.