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Twenty-four gestating spring calving cows grazing dormant native range were used to determine the effect of two different sources of DIP supplementation in the winter. Supplementation treatments were: 1) supplement containing urea as a source of non-protein nitrogen, 2) corn gluten feed (CGF) as a source of true protein, and 3) no supplement . Forage intake was greater for cows supplemented with urea compared to no supplement, and forage intake tended be greater for cows supplemented with urea than CGF. Microbial protein (MCP) synthesis estimated from urinary excretion of allantoin was greater for cows receiving urea than CGF or no supplement. However, efficiency of MCP synthesis did not differ among treatments and was approximately 8.5% of digestible organic matter intake.