Abstract 368

Jones,-RJ

CSIRO Div. Trop. Crops & Pasteure, Davis Lab., Private Bag, P.O. Aitkenvale, Qld 4814, Australia.

Plant toxicology. Proceedings of the Australia-U.S.A. poisonous plants symposium, Brisbane, Australia, May 14-18, 1984. 1985, 111-119; 42 ref. Yeerongpilly, Queensland, Australia; Animal Research Institute.

L. leucocephala, a palatable, tropical, leguminous browse shrub, contains mimosine, which is toxic to both ruminants and nonruminants. In the ruminant, however, mastication with alkaline saliva and incubation in the rumen result in both autolytic and microbial degradation of mimosine to 3-hydroxy-4(IH)-pyridone (3,4 DHP), a potent goitrogen of the thiouracil type which is excreted in the urine. In some tropical countries ruminants fed leucaena are able to degrade DHP in the rumen and so no DHP is found in the urine. The failure of ruminants to completely degrade DHP in Australia has been shown to be due to the absence of specific bacteria which are present in ruminants in Hawaii and Indonesia. Transferring rumen fluid, or mixed bacterial cultures derived from rumen fluid, to Australian ruminants has enabled complete ruminal metabolism of DHP with consequent prevention of hypothyroidism and other clinical signs associated with leucaena toxicity. The anaerobic bacteria involved are gram negative short rods. The implications of these findings in relation to other plant related toxicities are discussed.