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The study was conducted during the regular milk control of cows from the Bulgarian Brown Cattle (BBC) breed from the Agricultural Institute - Stara Zagora herd for the months of July and October 2014. Animals were divided into two groups according to the daily milk level - Elite group with a daily milking density of over 20 kg and a First group with a milk density of up to 20 kg. The ration consists of a total mix ration that was provided in the feeding racks. The milk urea content was determined in the laboratory of the Agricultural Institute - Stara Zagora by the Angelov, Ibrisimov and Milashki's method (1999). Milk samples for analysis were taken during the morning milking of the cows and studied immediately. The results of the survey were statistically processed with the STATISTICA for Windows software package. The study provides the opportunity to supplement information on the impact of protein and energy levels on the ration for maximizing the use of protein feeds effectively and limiting nitrogen losses in the environment. Concentration of crude protein above 16% in the dairy cow diet with sufficient energy for microbial growth, is associated with poor utilization of the protein - increase in urea level in milk above 20.0 mg/dl. Low levels of urea in milk - below 6.0 mg/dl are associated with insufficient amount of microorganism-accessible rumen protein (PBR), although the availability of enough energy in the diet. [ABSTRACT FROM AUTHOR]