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Urea in High Corn Silage Rations for Dairy Cattle^{1, 2,}

Michigan State University, East Lansing and Virginia Polytechnic Institute, Blacksburg

Abstract

Data has been presented showing that when urea added to the concentrate furnished 22 to 25% of the total dietary nitrogen for high producing dairy cows with corn silage as the principal forage, milk yields were depressed. Decreased palatability of concentrates has been reported when the urea content exceeded 2%. One report showed that pelleting urea with alfalfa meal was an effective manner of achieving high intakes of urea without having a detrimental effect on milk production and palatability of rations. Treatment of corn silage with 0.5% urea with a concurrent reduction in the crude protein content of the concentrate from about 18 to 13% did not result in depressed milk yields in several studies. Successful experiences in the field with urea-treated corn silage have largely substantiated these findings. Insufficient evidence is available for recommending treatment of corn silage with higher levels of urea, but favorable results were noted in one study when as high as 0.85% urea was added. Certain evidence indicates that the total NPN in the diet may be more important than the level of urea added per se. Performance of lactating dairy cows appears to be satisfactory when the total NPN of the diet does not exceed 0.45 kg./1,000 kg. bodyweight. Considering the wide variation in NPN content of forages (particularly silages) it appears that the upper limit of added urea is approximately 0.27 kg./1,000 kg. bodyweight. Further research on important factors affecting urea utilization could substantially alter allowable levels without depressing animal performance. Nitrogen losses in silages treated with urea were variable, but appeared to account for less than 10% of the added urea. Oven-drying of samples prior to Kjeldahl determination resulted in low estimates of nitrogen recovery, probably because of ammonia volatilization.

¹ Published with the approval of the Director of the Michigan Agricultural Experiment Station as Journal Article No. 4136.

² Invited paper presented at a joint session of the Southern Section, A.S.A.S. and the Southern Division, A.D.S.A., January 31, 1967, New Orleans, Louisiana.

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