Effect of urease immunity on growth, digestion and nitrogen metabolism in ruminant animals.

Abstract

Five trials involving 55 lambs were conducted to determine effects of subcutaneous injections of jackbean urease on antiurease production, general performance, digestion coefficients, nitrogen retention, plasma urea and ammonia levels and gastrointestinal fluids urease activity in sheep. Antiurease activity, based upon a technique involving the enzyme inhibition principle, was observed in serum of all urease injected lambs. Significant response in average daily gains was associated with production and maintenance of antiurease activity in blood. A total dose of 250 (International Union of Biochemistry, IUB) urease units per kilogram initial bodyweight, given by subcutaneous administration over a period of 3 to 4 weeks was considered suitable for this response. There was no significant effect of urease immunity on digestion of dry matter and organic matter and the retention of dietary nitrogen; however, the trends appeared to be toward increased digestibility in the immunized animals. In rumen infusion studies ruminal vein plasma ammonia-nitrogen levels were significantly lower in immunized lambs than in controls. Ruminal vein plasma urea level was not affected by urease immunity but peak values for jugular vein plasma urea levels in immunized lambs appeared to be obtained later than in the controls. Urease activity of fluid from the proximal end of colon of immunized lambs was lower than controls, and there appeared to be a trend toward decreased urease activity in rumen and ileum fluids of immunized lambs. The possible association of improved growth performance of sheep to a reduction of urea hydrolysis in the gastrointestinal tract is discussed.