EN
The impairment of the udder defense mechanisms causes an increase in the subclinical and clinical mastitis rate in dairy cows. The influence of some factors, that can depress leukocyte activity, on clinical mastitis occurrence rate during the first 8 weeks of lactation was studied on 313 dairy cows in one big farm. Thirty-nine per cent of the animals were affected with clinical mastitis. The predominant mastitis pathogens isolated were streptococci other than-Streptococcus agalactiae (41.25%), coagulase - negative staphylococci (11.25%) and coliforms other than Escherichia coli (9.37%). Most of mastitis cases appeared during the first 2 weeks of lactation. The cows in fourth and later lactations were more susceptible than younger animals. Also cows with mastitis in previous lactation were more often affected with this disease than animals with healthy udder. Retained placenta and subclinical ketosis did not increase the risk-of mastitis.