Comparison of three methods for the determination of urea in compound feed and silage

Abstract

Urea levels in compound feed were determined by three methods: the phenol-hypochlorite measurement of ammonium ions released by urease; the p-dimethylaminobenzaldehyde (DMAB) colour reaction with urea; and the Conway microdiffusion measurement of ammonia released by urease. The phenol - hypochlorite method had comparable accuracy and precision to the official DMAB method and was an improvement on the microdiffusion method. The phenol - hypochlorite method, produced as a clinical chemistry kit, can be used for the determination of urea in water extracts of compound feed and of chopped, fresh silage. This method is simple, rapid, inexpensive and may be automated for the determination of urea used as supplementary nitrogen in compound feed and silage.