Metabolism of Urea Nitrogen and Adaptation Response Trends In the Growing Wether And Steer

Abstract

Coombe et al. [6] demonstrated that when a urea solution was thoroughly mixed with hay, a 58.5 kg. Sheep was able to consume up to 100 gm. urea daily without ruminal ammonia reaching toxic levels. Ruminal infusion of 25 gm. urea in solution caused the ruminal ammonia to rise to toxic levels. Packett et al. [13] demonstrated that orally drenched urea caused a significant rise in ruminal and blood ammonia but urea mixed in the ration had no significant effect. Apparently the form in which urea reaches the rumen and the time required to mix with rumen liquor are important in urea nitrogen (N) utilization. Smith et al. [17] demonstrated that over a 50-day feeding period, sheep on a high urea diet showed a 0.2 per cent unit per day improvement in retention of absorbed N. McLaren et al. [11] summarized similar data with sheep where urea N supplied 78 to 70 per cent of dietary N, but other data with sheep [2, 4, 8] tended to demonstrate less of an adaptation response. The purpose of this study was first, to evaluate three methods of feeding urea on urea N metabolism in wethers and secondly to investigate possible mechanisms of adaptation associated with N metabolism in steers.