Abstract 494

Jones,-RJ; Hegarty,-MP

Division of Tropical Crops and Pastures, CSIRO, Davies Lab., PMB, PO Aitkenvale, Townsville, Queensland 4814, Australia.

Australian-Journal-of-Agricultural-Research. 1984, 35: 2, 317-325; 14 ref.

Steers were fed in pens on diets containing 0, 10, 20, 40, 67 and 100% Leucaena leucocephala for 112 days. The remainder of the diet was good quality sorghum hay. Liveweight change, feed intake, mimosine intake, urinary output of 3-hydroxy-4(1H)-pyridone (DHP), serum thyroxine (T4), serum triiodothyronine (T3) and effective thyroxine ratio (ETR) were estimated. Steers on the 67 and 100% Leucaena diets had low feed intakes (40 to 50 g/kg0.75), lost weight and were severely hypothyroid. Steers on 0, 10 and 20% Leucaena had intakes of 80 to 90 g/kg0.75, gained at 0.3 to 0.5 kg/day and showed normal thyroid function. Steers on 40% Leucaena had high feed intakes and grew well initially, but subsequently feed intakes and rates of gain declined. Reduced feed intake was associated with serum T3 levels below 1.0 nmol/litre. DHP excretion in urine was linearly related to Leucaena and mimosine intake. Recoveries of mimosine eaten, as DHP in the urine, varied from 33% with the 10% Leucaena diet to 55% with full Leucaena feeding. Feed intake declined as proportion of Leucaena in diet increased, but recovery of appetite was rapid when steers were transferred to a diet of sorghum and hay.