The effect of somatic cell count on the amount of daily milk yield and chemical composition of milk from 662 cows kept on 25 farms located in the region of southern Podlasie was analysed. A total of 5061 milk samples were evaluated. They were divided into four classes corresponding to the content of somatic cells in 1 ml of milk: <200,000; 201,000–400,000; 401,000–1,000,000; >1,000,000. It was found that, with an increase in the somatic cell count in 1 ml of milk, there was an increase in milk protein content from 3.36% to 3.54% and milk fat content from 4.02% to 4.16%, whereas the content of casein and dry matter in milk decreased from 2.56% to 2.45% and from 13.13% to 12.98%, respectively. Moreover, the percentage of casein in milk protein decreased from 76.2% to 69.2%. Also, milk yield was reduced, and the calculated losses in the milk yield resulting from an increase in the SCC were 10.6 to 17.3%.

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