The value of urea as a substitute for protein in the rations of dairy cattle: I. Field trials with dairy cows

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Abstract
1. A large-scale experiment with 274 dairy cows has been carried out to determine whether urea can be a substitute for part of the protein requirement of the lactating. dairy cow.2. It has been emphasized that any proteinsparing effect of urea or other sources of non-protein nitrogen can only be determined in the proteindeficient animal and one of the experimental treatments was therefore designed to supply well below that minimum requirement of protein compatible with milk production.3. The addition of protein to such a ration increasing the percentage of crude protein in the production rations from 12·9 to 17·9 and the protein equivalent from 9·5 to 14·5 resulted in a significant increase in milk production. This gave ample confirmation of the protein deficiency of the low protein ration.