Abstract 486

Jones,-RJ; Megarrity,-RG

Division of Tropical Crops and Pastures, CSIRO, Davies Lab., Private Mail Bag, Aitkenvale, Qld. 4814, Australia.

Australian-Journal-of-Agricultural-Research. 1983, 34: 6, 781-790; 25 ref.

To examine the apparent absence of toxicity in ruminants fed on Leucaena leucocephala in Hawaii, goats were offered comparable diets of Leucaena and lucerne chaff (control) in Australia and Hawaii during 7 weeks. Intake of mimosine, excretion of the ruminal metabolite 3-hydroxy-4(1H)-pyridone (DHP) and serum concentrations of thyroxine (T4) were estimated. Mean mimosine intake on the highest Leucaena diets in Australia and Hawaii were similar at about 20 g daily. In Australia, goats on the all-Leucaena diets became hypothyroid after only 3 weeks of feeding, thyroid glands were enlarged and erosion of the oesophageal mucosa and reticulo-rumen occurred. Excretion of DHP in the urine was related to the daily mimosine intakes, with recoveries of about 86%. In contrast, goats fed on Leucaena in Hawaii exhibited no clinical signs of toxicity and excreted less than 1% of the mimosine intake as DHP in the urine. No degradation of DHP occurred in vitro with rumen fluid from Australian goats, whereas 71% of the added DHP was degraded after 5 h with rumen fluid from goats in Hawaii. The results support the hypothesis that the differences observed are attributable to a different microbial metabolism of mimosine and DHP in ruminants in Hawaii.