Effects of molasses on mimosine metabolism in goats fed fresh and dried Leucaena with barley straw

Abstract

The effect of molasses supplementation on the metabolism and excretion of mimosine by goats was studied. Goats were fed barley straw and Leucaena (31.0 g mimosine kg-1 dry matter) throughout experiment 1 with and without a molasses supplement (400 g day-1). Four groups of four goats fed barley straw (13 days) were supplemented with either 0, 100, 200 or 400 g molasses day-1 for 6 days (experiment 2). Two goats on each molasses treatment were then offered similar quantities of Leucaena dry matter (DM) (10.0 g mimosine kg-1 DM) as either fresh or dried material for a further 18 days. Unsupplemented goats excreted appreciable quantities of mimosine and 3-hydroxy-4-(1H)-pyridone (DHP) in faeces. In experiment 1, 57% of the ingested mimosine was recovered, principally as conjugated DHP, in faeces and urine of goats supplemented with molasses, compared to 39% for unsupplemented goats. Molasses supplementation also increased the faecal excretion of conjugated DHP in experiment 2, particularly with goats fed dried Leucaena. Urinary excretion of mimosine in all goats was largely as conjugated DHP (negligible free DHP). The highest outputs of conjugated DHP in urine were associated with greater reductions in serum T4 levels, but 400 g of molasses supplement in experiment 2 prevented depressions in serum T4 levels. In both experiments a considerable proportion (c. 40%) of the ingested mimosine was not excreted.