Acta Veterinaria Scandinavica 2006, 48:22 http://www.actavetscand.com/content/48/1/22 80 70 60 50 40 30 20 10 0 major pathogens minor pathogens No bacteria SCC< 200 000 SCC 200 000 oFDriigspturorisbeiuti1tvioenfoorf bhaecatlethriyalagnrdomwtahstitic udder quarters negative Distribution of healthy and mastitic udder quarters negative or positive for bacterial growth. Coagulase negative staphylo- cocci C. bovis were considered as minor pathogens. Somatic cell counts (SCC) were measured by Fossomatic (n = 12,328). Other milking practices and some management proce- dures are described in Table 2. None of the above-mentioned properties or management procedures were statistically associated with the presence of certain bacteria. Discussion The farms in this study did not represent the usual type of Estonian farms, and the results should be compared only with farming in larger herds. The mean annual milk pro- duction (5,701 kg) in the herds of this study was some- what higher than the average production of cows in Estonia (4,766 kg). The mean age of the cows was seven months lower than the average age of Estonian cows. Table 2: Milking procedures and management practices in the 25 dairy herds studied. Herd variable No of milking units/milker ≤ 3 > 3 Gender of milker in farm Male only Female only both genders Participation in the dairy education program 1998 Using teat dipping Foremilk stripping Using teat ointment Teat cleaning with -water -washing solution -disinfectant solution n 18 7 1 21 3 20 7 25 5 14 7 4 % 72 28 4 84 12 80 28 100 20 56 28 16 None of the variables were statistically associated with the prevalence of mastitis. Herd sizes were bigger than the average in Estonia, where about 50% of the herds have less than 10 cows [10]. In this study, the mean size of herds was 164.4 cows and only three herds had less than 20 cows. It is usually difficult to compare results of surveillance studies because of differences in the sample selection and the criteria of mastitis. This study was carried out in a sim- ilar fashion as mastitis surveys in Finland in which a threshold level of 300,000 cells/ml were used for mastitis as suggested by Klastrup and Schmidt Madsen [6,11,12]. New data indicate, however, that the SCC of a cow that is not infected with mastitis pathogens is usually < 200,000 cells/ml and therefore this threshold level was used in this study [7,8]. To compare these results with the Finnish studies, we calculated mastitis prevalence also with a threshold level of 300,000 cells/ml. Thus the percentage of cows having mastitis in one or more quarters was 43.5% (95% confidence interval, 39.3 to 47.3), which was slightly higher than in Finland where the corresponding figure was 38% (95% confidence interval 35.1 to 40.5) in 1995 and 31% (95% confidence interval 28.4 to 33.1) in 2001 [11]. The mean SCC value as calculated from individual quarter milk samples appeared higher than that measured from the bulk milk (p = 0.07). The reason for this may be the fact that milk from cows suffering from acute clinical mas- titis may have been treated with antibiotics and the milk discarded. Therefore the SCC of tank milk can give too optimistic a figure of the herd mastitis situation if it is the only measurement criteria. In the study conducted by Klaassen et al study, only 7.8% exceeded one million cells/ ml (cow sample), which could be explained by the fact that in their material, milk samples were only collected from milk supplied to dairy plants [2]. In this study, 20.7% of cows had more than one million cells/ml (the average of quarter milk samples). C. bovis was the most common bacterial finding in the study, which is in line with the Finnish study by Pitkälä et al. [11]. Honkanen-Buzalski et al. showed that C. bovis infec- tion levels can differ considerably between herds, and that C. bovis infections are most common in herds not using teat dipping [13]. In this study, only 7 out of 25 herds used teat dipping, which may explain the high prevalence of C. Bovis. However, statistically significant differences were not detected. In a study conducted by Aasmäe et al., C. bovis was only found in 0.6% of the samples, but milk samples having less than 300,000 cells/ml were not inves- tigated [3]. As C. bovis infections are normally mild, they may remain undetected [14]. The mean SCC of quarters with C. bovis was 303,000/ml. However, only 27.4% of the quarters with C. bovis infection had SCC ≥200,000/ml. In quarters infected with major udder pathogens, the Page 4 of 6 (page number not for citation purposes)