The effect of supplementary nickel on urea metabolism in sheep given a low protein diet

ABSTRACT Work in the United States of America has shown that dietary supplements of nickel (Ni) can result in an increase in rumen urease activity and can increase growth rate and food conversion efficiency in lambs and steers given low protein diets. It has been suggested that Ni enhances urea recycling through its effect on urease activity. To examine this hypothesis, four sheep were given a high-energy, lowprotein diet with or without a supplement of 5 mg/day Ni, given as NiCl2.6H2O by continuous infusion into the rumen. Urea irreversible loss rate (ILR) and pool size were measured by means of a single intravenous injection of 14C-urea. The addition of Ni resulted in a significant increase in rumen urease activity (P< 0·05) but there was no significant effect on urea ILR, urea pool size, urinary urea excretion or on the quantity of urea recycled to the gastro-intestinal tract. Ni also had no effect on plasma urea or rumen ammonia concentrations, on diet digestibility or on nitrogen retention. It is concluded that the enhancement of urease activity by supplementary Ni conferred no nutritional advantage to the sheep.