The experiment was conducted on a farmlocated in the Province ofWarmia andMazury (NE Poland) over the years 2004–2006, on a group of 92 Polish Holstein-Friesian cows with 287 completed lactations. The aim of the study was to determine some performance traits of these cows as dependent on their maximum daily milk yield during successive 305-day and full lactations. The cows were divided into three groups: group 1 – cows with a maximum lactation milk yield ≤ 20 kg, group 2 – cows with a maximum lactation milk yield from 20.1 kg to 30 kg, group 3 – cows with a maximum lactation milk yield > 30 kg. The most cows were culled during the second and third lactation (67.39%). The highest mean daily milk yield was recorded in group 3, reaching a peak during the third lactation (40.23 kg). The productivity of cows was found to increase until the third lactation. It was at the highest level in group 3: 8684 kg of milk, 8887 kg of ECM, 574 kg of fat and protein, at milk fat and milk protein content of 4.21% and 3.38%, respectively. The highest concentrations of milk fat and milk protein were observed in the group of cows with the lowest daily yield, i.e. ≤20 kg of milk. The mean length of the first three inter-pregnancy and inter-calving intervals was within a normal range. In consequence, both the production and reproduction cycle did not exceed 365 days. The highest coefficients of correlation were noted between milk yield and fat yield (r = 0.92), protein yield (r = 0.98) and dry matter content (r = 0.99). An increase in milk yield was accompanied by a decrease in protein content (r = 0.07) and a slight increase in the levels of fat (r = 0.25) and dry matter (r = 0.16). The milk performance traits of cows had no significant effect on the length of the inter-pregnancy and inter-calving intervals, which were found to be positively correlated with the insemination index values (coefficients of simple correlation: 0.38 and 0.54, respectively, at a significance level P ≤ 0.05).

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