Journal of Animal Science, Vol 73, Issue 1 257-266, Copyright © 1995 by American Society of Animal Science

JOURNAL ARTICLE

Fractionation of nitrogen isotopes by mixed ruminal bacteria

M. A. Wattiaux and J. D. Reed
Department of Dairy Sciences, University of Wisconsin-Madison 53706.

Mixed ruminal bacteria were cultured with glucose, cellulose or no carbohydrate, and ammonium bicarbonate or casein hydrolysate. Changes in amounts of bacterial ammonia and non-ammonia N were measured. Ratios of N isotopes expressed as delta 15N (delta 15N) were measured by isotope ratio mass spectrometry. When bacteria were cultured with glucose and ammonium bicarbonate, bacterial delta 15N decreased from .9 to -5.8/1000 and residual ammonia delta 15N increased from -1.4 to 12.7/1000. Fractionation of N isotope occurred during ammonia incorporation because the difference between delta 15N of ammonia and delta 15N of bacteria (delta 15N) was 18.8/1000 (P < .01). However, when casein hydrolysate was the N source, delta 15N between non-ammonia and bacteria averaged only 1.3/1000 (P > .1), indicating no fractionation of N isotopes occurred during utilization of amino acids. The amount of bacterial N was highest at 24 h of incubation when cellulose was the carbohydrate source. At that time, delta 15N between ammonia and bacteria was 8.9/1000 when ammonia was the N source, but delta 15N between non-ammonia and bacteria was 1.7/1000 when casein hydrolysate was the N source. Bacterial N decreased after 24 h when cellulose was the source of carbohydrate. Results indicate that fractionation of N isotopes occurred during ammonia incorporation, but not during incorporation of N from amino acids, deamination, and release of ammonia. Fractionation of N isotopes during incorporation of ammonia N may be used as a marker to study N metabolism by ruminal bacteria.

This article has been cited by other articles:

				P. J. Gunn, A. D. Weaver, R. P. Lemenager, D. E. Gerrard, M. C. Claeys, and S. L. Lake Effects of dietary fat and crude protein on feedlot performance, carcass characteristics, and meat quality in finishing steers fed differing levels of dried distillers grains with solubles J Anim Sci, September 1, 2009; 87(9): 2882 - 2890. [Abstract] [Full Text] [PDF]

				N. A. Cole, P. J. Defoor, M. L. Galyean, G. C. Duff, and J. F. Gleghorn Effects of phase-feeding of crude protein on performance, carcass characteristics, serum urea nitrogen concentrations, and manure nitrogen of finishing beef steers J Anim Sci, December 1, 2006; 84(12): 3421 - 3432. [Abstract] [Full Text] [PDF]

				C. W. Hastad, S. S. Dritz, M. D. Tokach, R. D. Goodband, J. L. Nelssen, J. M. DeRouchey, R. D. Boyd, and M. E. Johnston Phosphorus requirements of growing-finishing pigs reared in a commercial environment J Anim Sci, October 1, 2004; 82(10): 2945 - 2952. [Abstract] [Full Text] [PDF]

				J. F. Gleghorn, N. A. Elam, M. L. Galyean, G. C. Duff, N. A. Cole, and J. D. Rivera Effects of crude protein concentration and degradability on performance, carcass characteristics, and serum urea nitrogen concentrations in finishing beef steers J Anim Sci, September 1, 2004; 82(9): 2705 - 2717. [Abstract] [Full Text] [PDF]

				M. Gonzalez-Ronquillo, J. Balcells, J. A. Guada, and F. Vicente Purine Derivative Excretion in Dairy Cows: Endogenous Excretion and the Effect of Exogenous Nucleic Acid Supply J Dairy Sci, April 1, 2003; 86(4): 1282 - 1291. [Abstract] [Full Text] [PDF]