In the research urea content in milk and frequency of the occurrence of samples with different urea level in milk of cows fed on total mixed ration (TMR) and traditional system in summer and winter season were analyzed. Analysis covered 14272 of milk samples. On account of urea level they were divided on three groups: to 140, 141-250 and above 250 mg of urea in 1 liter of milk. It was found that average urea content in milk of cows fed on total mixed rations (TMR) amounted to 196 mg.l-1. Milk of cows from farm applying traditional feeding system included 184 mg.l-1 of that constituent average. Both these values therefore could have been recognized as optimal. Urea level pointed out to the energy-protein unbalancing of
feed rations in 55.6% (TMR) and 57.7% (traditional) of milk samples.
Urea level in milk of cows fed in traditional system was at p≤0.01 higher (196 mg.l-1) in summer than in winter season (166 mg.l-1). In winter feeding season the frequency of the occurrence of milk samples indicating the lack of protein in feed rations (to 140 mg of urea in 1 liter) was 11.9% higher than in summer season.
