Producer Question from 2010
Q: Can cattle grazing on winter range grass or cornstalks utilize NPN in a lick tub or do cattle utilize all natural tubs better? (December 29, 2010)
A: Cows on stalks will be able to use some NPN. NPN supplies a source of nitrogen so that the rumen microbes can make their own protein. For them to make their own protein cows need nitrogen (supplied by NPN) and a carbon chain to make the protein. The carbon chain comes from energy that the cattle eat, in this case some grain, husk, and leaves. The key for microbes is that the nitrogen source is available at the same time as the energy source. NPN is readily available when it enters the rumen, so the carbon chain from the energy source needs to be available at the same time. When NPN is used in a feedlot diet, the NPN is almost 100% utilized because the energy is coming from grain and it is easily digested making the carbon chain there at the same time as the NPN source. In a forage situation, the forage is high in fiber and broken down at a much slower rate, so the utilization of the NPN is not as efficient. So bottom line, cows supplemented with NPN while grazing corn stalk residue will use some of the NPN.
The question really is, do cows need to be supplemented protein while grazing corn stalk residue? Our data would suggest, that if cows are BCS 5 or greater when they begin grazing the corn stalk residue and the stalk field is stocked with cattle at recommended rates, we have not observed a response on the cows performance when they were supplemented with protein.
There are data that suggest an effect of protein supplementation in late gestation on the fetus that the cows are carrying. There is less of a positive effect (no negative effect) on the gestating fetus for cows supplemented and grazing corn stalks during late gestation compared to cows supplemented and grazing winter range.
For more information, please see the Supplementing Beef Cows Grazing Cornstalk Residue with a Distillers Based Cube (PDF 102KB) article from the 2008 Nebraska Beef Cattle Report.
Dr. Rick Rasby, Professor of Animal Science
Animal Science, University of Nebraska–Lincoln, Lincoln, NE