Risk factors associated with clinical mastitis in low somatic cell count British dairy herds.

A cross-sectional survey of dairy farms with low bulk milk somatic cell counts was carried out to assess the level of clinical mastitis and to quantify risk factors associated with the incidence rate of clinical mastitis. Questionnaires were sent to 3009 milk operations with an annual mean bulk milk somatic cell count of less than 100,000 cells/ml during 1997. A response rate was 61%. The mean incidence of clinical mastitis reported was 22.8 cases per 100 cows/yr. Negative binomial regression models were used to assess statistically significant risk factors associated with the incidence of clinical mastitis. The incidence increased when farmers reported that they had straw yard housing for milking cows (compared with cubicle housing), mucked out the calving area less frequently than once per month, kept cows standing in a yard after milking, always practiced postmilking teat disinfection, had greater than 50% replacement rate, had some cows that leaked milk on entry to the parlor, had some cows that leaked milk at other times, and foremilked before cluster attachment. The incidence of clinical mastitis was lower on farms when the gathering yard used before milking was scraped at least twice a day, cows were offered feed after both milkings, rubber gloves were not worn during milking, teat liners were changed after 6000 milkings, and the average dry period was less than 40 d. The study has identified areas of the environment in which efforts to improve hygiene should be focused.