Milk from 574 Holstein-Friesian cows constituted experimental material. The animals came from two cowhouses. At one cowhouse cows were kept in the loose housing system. On the other farm cows were kept under the indoor keeping system in a shallow cowhouse with stalls of medium length. A total of 3 552 samples were collected from cows being in their first to sixth lactations. The percentages of fat and protein, and the somatic cell count were determined. The number of cell elements was assessed using the direct method with the CombiFoos apparatus. In the study the dependencies between the number of somatic cells in milk and the daily yield and composition of milk were investigated. The effect of age group and management system on milking performance traits and the number of somatic cells in milk were assessed in the study. It was found that the health condition of the mammary gland, evaluated on the basis of the somatic cell count in milk has a significant effect on the daily milk yield and fat content in milk. The cows whose milk contained the lowest number of somatic cells were distinguished by the higest daily milk and the lowest protein contents. A lower number of cell elements in the milk of heifer cows was shown in comparison to multiparous cows, as well as the milk of cows kept under the loose housing system in comparison to the indoor keeping system.

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