Problems in Feeding Urea to Ruminants

Abstract

The problems in feeding urea to ruminant were discussed in view of current knowledge concerning the metabolic aspects of N utilization. Specific items cons idered were urea hydrolysis, utilization of ammonia, ammonia absorption, urea recycling, urea toxicity, quality of microbial protein, limiting amino acids, adaptation response, influence of urea on intake, and maximum levels for high production. The thermodynamic limitations imposed by the anaerobic nature of the rumen may be a limiting factor in attempting to obtain comparable rates of urea hydrolysis and fixation of liberated ammonia into cellular protein. Inability of the rumen microorganisms to synthesize sufficient quantities of all amino acids needed to prevent deficiencies or imbalances may contribute to lowered animal performance. Clarifying the magnitude of the urea-recycling mechanisms under various dietary conditions and elucidating the specific tissues involved in the adaptation response are paramount to effective utilization of urea. From an economic viewpoint, it is important not only to use nonprotein rather that protein N sources but also to derive a considerable portion of dietary carbohydrate from sources that cannot be used directly by man.