The effects of intravenous urea infusions on nitrogen metabolism in sheep

Abstract

The effects of intravenous infusions of measured amounts of urea solution into sheep, providing c. 5 g urea nitrogen per day, were studied in sheep on four rations differing in crude protein and readily available energy content. Nitrogen balances, water intakes, urea nitrogen excretions, and diurnal variations in plasma urea and rumen ammonia levels were compared over 8-day collection periods. When corn starch and dried molasses provided readily available energy in addition to crushed pure cellulose the retention of infused urea nitrogen was 50 % compared with 40 % with crushed pure cellulose. It is suggested that as nitrogen retention was similar to the increases in nitrogen balance, the nitrogen retained was first transported into the rumen, where it was synthesized to microbial protein. Thus corn starch, molasses, and crushed cellulose provided suitable energy levels for utilization of the extra nitrogen by the rumen micro-organisms. On a low protein, all roughage ration the nitrogen transferred into the rumen produced increased rumen ammonia levels and was subsequently reabsorbed and excreted in the urine.