ABSTRACT Urea is by far the most used form of non-protein nitrogen in ruminant rations, providing an inexpensive source of crude protein. Urea is hydrolyzed in the rumen mostly to ammonium (NH4+) and very small amount of ammonia (NH3). Although both substances are very similar, the single deprotonation of ammonium to ammonia turns this last compound lipophilic and highly absorbable. This deprotonation occurs in reasonable proportion when the ruminal fluid pH is high. Poisoning occurs whenever large quantities of ammonia is formed and absorbed into the bloodstream. This article reviews some chemical aspects of ammonium, urea and especially ammonia its generation within the rumen, absorption, metabolism, harmful effects, and detoxification mechanisms. A comprehensive report of the pathogenesis, clinical picture, laboratory and post-mortem findings, diagnosis, new perspectives of treatment, and preventive measures of the acute ammonia poisoning are described.
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