EN
Milk yield of all the cows from selected herds, kept in various areas polluted by a copper smelter was analysed. The herds studied were divided into 3 groups according to the degree oat pollution of the area. Milk yield of 625 cows was examined. The cows started production in 1978-82 and followed the first three lactations. Milk yield was corrected for the season and age of calving. The data enabled the calculation of the means of milk and fat yield for various groups of cows and the estimation of significance of differences. The studies have shown the differences in annual yield and full lactation yield among the cows kept in various areas. The lowest milk and fat yield was found in the area characterized by the highest pollution with heavy metals. The lowest increase in milk and fat yield was abserved in the third lactation compared to the first one. The results have proved unfavourable effect of a copper smelter on milk yield of the cows kept in the vicinity of a copper smelter.