Non-protein nitrogen in the feeding of cattle

Abstract

Protein is the first-limiting nutrient in cattle production worldwide. Urea and other non-protein nitrogen (NPN) compounds, which can be hydrolyzed to ammonia, can be used to replace natural protein in cattle diets. Ammonia is the common denominator when the mode of action is determined for NPN compounds. A stepwise presentation of the hydrolysis and use of urea to produce microbial protein is used as an example of ammonia utilization. Urea is a widely used NPN compound; thus, factors which affect urea utilization were discussed as follows: 1) Level and solubility of dietary protein; 2) Kind of dietary carbohydrate; 3) Level of dietary fat; 4) Adequacy of dietary minerals and vitamins and presence of antibiotics and diethylstilbestrol; 5) The effect of rate and frequency of feeding. The practiced usage of urea in beef and dairy cattle nutrition is discussed, with emphasis on ration conditions which promote urea utilization. It was pointed out that urea, when fed at too high a level, will cause ammonia toxicity in cattle. Urea toxicosis is rapid and acute, but present experimental evidence does not support the idea that urea causes chromic toxicity in cattle. The clinical course of urea toxicity is described and suggestions for possible treatments were made. Oral administration of five to ten gallons of cold water appears to be one of the best treatments and reasons for its beneficial effects were discussed. There does not appear to be any effect of “near toxic” levels upon the incidences of abortions or upon the subsequent reproductive performance of cows which survive urea over-dosage. The common misconceptions of veterinarians and livestock producers were considered and discussed. Also, the uses of biuret, ammonium sales and ammoniated products were discussed.