The following information appears on a feed tag of a protein supplement. Because the feed is a protein supplement, the name on the tag usually indicates the percentage protein that the supplement contains. As an example, let’s evaluate the feed tag of a medicated protein supplement called Protein Gem Fortifier 32-10 B70. The 32-10 indicates that this supplement is a 32% protein supplement and that 10% comes from a non-protein nitrogen source; therefore 22% coming from an all “natural” protein source (see the example below). The guaranteed analysis will indicate that this feed has a “Min.” (minimum) of 32% crude protein.
As an example from a feed tag:
Crude Protein (not less than) 32%
Protein Equivalent from NPN (not more than) -10%
Amount of Natural Protein 22%
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 if the NPN source is urea. 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 10% NPN and, again, let’s assume that the NPN source is urea, so 10%/2.81 = 3.55%; therefore is supplement is 3.6% 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 0.036 = 0.036 lb/hd/day urea. When supplementing cows protein in range conditions when it is warranted, the supplement should contain only small amounts of urea.
The most common NPN source in cattle feeds is urea. Urea is not protein, but provides a nitrogen source so that the rumen microbes can make their own protein. There are enzymes in the rumen that allows the nitrogen source to be cleaved away from the urea and the microbes incorporate the nitrogen with a carbohydrate chain to make bacterial protein. A component of all protein is nitrogen. A question may be, do cattle use the bacteria as a protein source? The answer is yes. The bacteria flow from the rumen to the small intestine where they are broken down by digestive enzymes into amino acids and the amino acids are absorbed across the wall of the small intestine. In the research world, this is called bacterial crude protein.
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