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Adaptation of Stocker Calves to Non-Protein Nitrogen Diets as a Result of Grazing Wheat Forage

U.S. Department of Agriculture, El Reno, OK 73036

Abstract

Two trials using 24 heifers (trial 1) and 30 steers (trial 2) were conducted in separate years to determine if consumption of wheat forage resulted in an adaptation to non-protein N (NPN) diets containing urea or ammonium sulfate. During phase I of each experiment, 12 heifers (trial 1) and 20 steers (trial 2) grazed wheat forage (WF) for 45 d, while the remaining animals (C) were fed a control diet in drylot before all animals were abruptly shifted to a NPN diet for 50 d (phase II). The amounts of soluble N and NPN in wheat forage as a percentage of the total N were 35.1 and 15.6 for trial 1 and 26.5 and 21.4 for trial 2, respectively. Dry matter percentages were 27.4 and 27.8 and crude proteins (% of dry matter) were 25.3 and 35.1 for trials 1 and 2, respectively. Ruminal ammonia and NPN concentrations were higher (P<.01) for the WF animals than the C animals during phase I and decreased with time (P<.01). Plasma urea N also declined with time (P<.05), but plasma protein concentration increased (P<.05) in the WF animals during phase I. It appeared that an adjustment was being made to the higher soluble N content of the wheat plant by d 30 (trial 1) and d 45 (trial 2). However, based on ruminal and blood measurements, WF animals were not adapted to the urea or ammonium sulfate fed during phase II. The response of the WF animals to changing to a NPN diet was similar to the C animals in terms of concentration changes of ruminal ammonia and NPN and plasma urea N and protein, but the WF animals gained more weight (P<.05) when fed urea than the C animals without consuming more dry matter. Thus stocker calves that have grazed wheat forage are more efficient during the first 50 d of the finishing or growing phases than calves that have not, but the utilization of urea appears to be similar.

¹ USDA-ARS, Livestock and Forage Res. Lab., P.O. Box 1199.

² Mention of a specific product or piece of equipment does not constitute an endorsement by the J-USDA and does not imply their approval to the exclusion of other products that may be suitable.

This article has been cited by other articles:

				W. A. Phillips and G. W. Horn Intake and digestion of wheat forage by stocker calves and lambs J Anim Sci, September 1, 2008; 86(9): 2424 - 2429. [Abstract] [Full Text] [PDF]