Acta Veterinaria Scandinavica 2006, 48:22 http://www.actavetscand.com/content/48/1/22 as dependent variables and the data collected in the ques- tionnaire were used as independent or categorical varia- bles. Each variable was first analysed pairwise using t-test, the analysis of variance or correlation depending on the data structure. Their overall effect was further evaluated by analysing parameters using stepwise regression. Only the significant findings of regression analysis are reported. The statistical analysis was carried out with Statistix soft- ware (Analytical software, Tallahassee, USA). Results Somatic cell counts The distribution of healthy and mastitic udder quarters with or without bacteria is shown in Figure 1. The propor- tion of quarters having SCC ≥200,000/ml was 25.3% (95% confidence interval 22.3 to 28.3) (Fig. 1). The per- centage of cows having mastitis in one or more quarters, as measured by SCC, was 52.7% (95% confidence inter- val, 47.9 to 57.6). The average SCC calculated from quar- ter milk samples weighted by milk production was 370,120 cells/ml (95% confidence interval 313,970 to 426,270). Mastitis pathogens The distribution of bacterial findings in 11,640 quarter milk samples, the proportions of bacterial isolates and the corresponding SCC are shown in Table 1. Samples with mixed cultures were excluded from these figures as these quarters cannot be categorised either as healthy or mas- titic. Corynebacterium bovis was isolated in 14.6% of the samples and was the most common bacteria isolated (47.3% of isolates). Staphylococcus aureus was isolated from 6.5% of the samples and coagulase negative staphy- lococci from 4.9%. Streptococci were less frequent iso- lates. Table 1: Bacterial findings during the survey. Bacterial isolate Streptococcus agalactiae Streptococcus dysgalactiae Streptococcus uberis Other streptococci, Enterococci Staphylococcus aureus Coagulase-negative staphylococci Corynebacterium bovis Coliforms Actinomyces spp. Other bacteria No growth 110 68 86 208 752 568 1,694 20 7 68 8,059 Herds, milk production and management procedures The cow breeds in the investigated 25 herds were Estonian Red, and Estonian Holstein. Fourteen herds included both breeds, two herds contained only Estonian Red, and nine herds only Estonian Holstein. The average herd size was 164.4 cows, ranging from 15 to 463. The average age of the animals was 5.3 years. All herds are catalogued in the Estonian Animal Recording System. According to the data, the average production/cow was 5,520 kg/year. The latest bulk milk SCC value of the herds before the farm visit averaged 304,560 cells/ml (95% confidence interval 250,400 to 358,700), ranging from 69,000 to 730,000 cells/ml. The animals were kept in tie-stall housing (88% of ani- mals) at 22 farms, and only three herds had loose hous- ing. Only two herds were not pasturing. The bedding material was sawdust in 32%, straw in 16%, cut straw in 4%, peat in 8% and a combination of the previously men- tioned materials in 40% of the herds. All herds had solid manure removal. Peat bedding was associated with higher mastitis prevalence (p < 0.01). The farms had seven different milking machine types. The age of the milking machines varied from one to 22 years. The milk claws were smaller than 150 ml in 16% of the milking machines. All milking machines had been serv- iced after 1996 and 80% of the milking machines had been vacuum tested during the previous year. The average number of milking units/milker was 3.6, with a minimum of two and maximum of 16. The average number of cows/ milker was 64.2, with a minimum of 15 and maximum of 155. Only seven farms used teat-dipping. Women as farm owners, and participating in the milking, were associated with lower mastitis prevalence at the farms (p < 0.05). 0.9 0.6 0.7 1.8 6.5 4.9 14.5 0.2 0.1 0.6 69.2 3.1 1.9 2.4 5.8 21.0 15.8 47.3 0.6 0.2 1.9 3,263 (5,596) 2,576 (4,041) 2,431 (4,452) 1,706 (3,100) 1,026 (2,070) 508 (1,765) 303 (956) 5,401 (5,423) 12,579 (9,262) 565 (2,165) 221 (961) No of samples N = 11,640 % of all samples % of isolates N = 3,581 SCC *103/ml (SD) The figures in the first two columns are the numbers and percentages of all quarter milk samples. The third column represents percentages of bacterial isolates. Mean SCC (SD) for each group are also presented. Page 3 of 6 (page number not for citation purposes)