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A Comparison of Nitrogen Metabolism and Ammonia Toxicity from Ammonium Acetate and Urea in Cattle^{1, 2,}

Kansas State University, Manhattan 66502

Abstract

CONCENTRATIONS of rumen ammonia, blood urea and rumen pH resulting from intraruminally administering urea or ammonium acetate into rumen-fistulated cattle were compared. Ammonium acetate gave greater rumen ammonia concentrations than did isonitrogenous quantities of urea. Urea elevated rumen pH, but ammonium acetate did not. Each increased concentrations of ammonia and urea in peripheral blood.

Simultaneously administering molasses with either of the two compounds reduced rumen ammonia concentrations and rumen pH, and markedly reduced blood ammonia. Blood urea concentrations also were reduced by adding molasses. Apparently molasses increased nitrogen utilization by rumen microorganisms and decreased ruminal pH thus reducing the rate ammonia was absorbed from the rumen.

Toxicities resulting from intraruminally administering ammonium acetate or urea also were compared. Smaller nitrogen equivalent doses of urea than of ammonium acetate produced toxicity. A relationship between peripheral blood ammonia concentrations and toxicity was clearly indicated. Severe toxicity occurred when blood ammonia-N concentrations exceeded 0.7 to 0.8 mg/100 ml.

The effect of rumen pH on ammonia absorption from the rumen may explain some of the apparent differences in toxicity between the two compounds. Administering urea increased rumen pH and thus predisposed animals to rapid ammonia absorption. No immediate changes in rumen pH resulted from ammonium acetate so greater concentrations of rumen ammonia were required after ammonium acetate than after urea for absorption of ammonia sufficient to cause toxicity.

¹ Contribution No. 821, Department of Dairy and Poultry Sciences, Kansas Agricultural Experiment Station, Manhattan.

² Supported in part by a grant from Gulf Research and Development Co., Kansas City, Kansas. The assistance of Dr. L. V. Phillips, Dr. K. P. Dubrovin and Mr. E. A. Woods is gratefully acknowledged.