Daily supplements of dried Leucaena leaf meal (500 g/head) were offered for 3 weeks to steers in metabolism cages. The steers had previously been fed diets of oaten chaff (5 kg/head/day) ormclasses and urea (4·5 kg/head/day) with restricted forage (2 kg/head/day). Excretion rates of the primary degradation product of mimosine, 3-hydroxy-4(1H) pyridone (DHP) by steers fed the two diets were compared. These compounds appeared in urine on the 1st day after Leucaena feeding had commenced and output remained fairly constant after 4 days. Mean weekly urinary outputs (g) of DHP from steers fed the oaten chaff or molasses + urea diet were 13·45 and 7·50 respectively. These levels corresponded to 0·23 and 0·13 of the amounts ingested. When steers were fed the molasses + urea diet, DHP continued to appear in urine up to 5 days after Leucaena had been withdrawn from the diet. On the oaten chaff diet no DHP was detected after 3 days following withdrawal of Leucaena.
The effects of casein or formaldehyde-treated casein supplements on the output of urinary DHP by steers fed oaten chaff plus Leucaena was evaluated in a second experiment which ran concurrently. The animals were fed the test diets for 3 weeks before collections were made. Mean DHP outputs (g/day) from animals fed the control diet, control diet plus casein or control diet plus formaldehyde-treated casein were 1·89, 2·21 and 2·44 respectively.
These results confirm substantial degradation of DHP and that the extent of degradation can be affected by the dietary regime in which Leucaena is fed.