Abstract: In order for food to be used as soon as possible and as well as possible, it is very important that the silage that feeds the animals is prepared in such a way that it contains as much degradable protein as possible in relation to non-degradable proteins. The paper analyzes the influence of the addition of non - protein nitrogen (NPN) to the silage of the whole maize plant on the content of individual protein fractions. Of the NPN compounds, urea (at a concentration of 0.5% and 1%) and Benural S (at a concentration of 1% and 2%) were used. The amount of insoluble proteins and non-protein nitrogen in the silage increased with the addition of NPN compounds.