EN
The aim of this paper was to investigate the impact of clinical lameness in Polish Holstein-Friesian dairy cows on milk yield as well as on fat, protein, and lactose yields during early lactation (120 d). The dataset includes 312 monthly test-day milk yields and milk composition records from 78 cows, which calved from October 2008 to April 2009. Twice a week, during the first 120 d postpartum, the cows were examined for lameness and they were scored fortnightly according to a 5-point locomotion scoring system. Factors affecting milk yield and milk components included calving season, parity, month of lactation, and degree of lameness. In cows, which were clinically lame for a month and which were clinically lame for more than a month (maximum per 2 months), the total mean reduction in milk yield per 120-d lactation was approximately 308 and 283 kg, respectively, as compared with cows, which were never lame in early lactation.