The study was performed on the Black and White cows with a different proportion of genes of Holstein-Friesian cattle, and involved high yielding cows with a test day production up to 40 kg of milk. During the performed study, we determined the urea level in milk, which informed about the protein supply to cows, and the protein level in milk, which informed about the energy supply to cows. In cow feeding, an important and objective indicator of the properly balanced feed ration in respect of protein and energy is a urea level. Its mean content in milk of the examined population ranged from 242 to 269 mg · l–1 over individual examination periods. Evaluation of the feed ration balance in respect of protein and energy showed the existence of protein deficiency ranging from 152 to 361 g with the simultaneous energy deficiency ranging from 24.4 to 31 NEL (MJ). It was not found however, that the urea content in milk of the examined population exceeded the standard (150–300 mg · l–1).

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