Abstract
It has been known for half a century that urea can usefully supplement the diet of ruminants, but only comparatively recently has there begun to be a clear understanding of the dietary circumstances in which this is advantageous. Urea acts not directly but as a source of nitrogen for the synthesis of protein by micro-organisms in the rumen, and its effect on growth—often reducing loss of weight rather than actually increasing it—depends on, among other factors, the concentration of biodegradable nitrogen in the basic diet and the resistance of forage to digestion. Sulphur metabolism and genetic factors are also involved.
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