Too much urea in range cubes, nitrates in volunteer corn?

Producer Question from 2010

Q:  I have purchased some range cubes that are 37% protein (w/8% Urea). If I feed 3 lbs. per head every other day, will I have any problems with too much urea or ammonia in the blood? Also, is volunteer corn high in nitrates? (October 8, 2010)

A:  I assume on the feed tag it reads, Protein supplement 37-8, so:

  • Crude Protein (not less than) 37%
  • Protein Equivalent from NPN (NPN=urea, not more than) - 8%
  • Amount of Natural Protein 31%

You can determine the proportion of the protein in a supplement that is supplied by the NPN source(s) by dividing the percentage of protein equivalent from non-protein nitrogen by 2.81. Urea is 281% crude protein equivalents, so the decimal of 281% is 2.81 (move the decimal two places to the left to convert a percentage to a decimal). The above feed tag is 8% NPN and the NPN source is urea, then, 8%/2.81 = 2.85%; therefore is supplement is 2.85% urea.

To determine the amount of urea that is being supplied, simply multiply the percentage by the pounds fed. In this case, if the supplement is being fed at 1 lb/hd/da x 0.0285 = 0.0285 lb/hd/day urea.

Remember, urea is brokendown in the rumen and the rumen microbes combine it with energy to make their own protein. Data would suggest that a small amount of urea can be used in forage diets to meet the protein needs. I assume that you will be using it to supplement range that is decreasing in nutrient value.

This amount of urea in a protein supplement for cows on range diets should be ok. As always make sure all cows have the opportunity to consume their fair share. If fed every-other-day, blood urea nitrogen levels should not be a problem.

I would assume that all or most of the nitrogen applied this spring would have been used by the corn crop that was harvested and there would be very little nitrogen for the volunteer corn. The only way there would be much nitrogen left over would be if the corn were hailed early in the growing season or there was drought and the corn did not take-up the nitrogen that was applied in the spring. Enevn then, the excess nitrogen likely leached down the soil profile.

Dr. Rick RasbyDr. Rick Rasby, Professor of Animal Science
Animal Science, University of Nebraska–Lincoln, Lincoln, NE