Acta Veterinaria Scandinavica 2006, 48:22 http://www.actavetscand.com/content/48/1/22 choses has also resulted in the bankruptcy of many dairy plants. The ability of small farms to invest in farm improvement is much more limited than that of bigger farms, resulting in differences between management prac- tices, equipment and even in the feeding of cows. After the political changes described above, few studies of mastitis have been carried out on Estonian dairy herds. Tilga and Raid examined 2,420 milk samples during the years 1988–1991, and found that 5% of Estonian cows had clinical mastitis and 15–30% subclinical mastitis [1]. Their criteria for a mastitic cow was ≥ 500,000 cells/ml in a milk sample. Staphylococci were the most prevalent pathogen (34%) in their study. Klaassen et al. studied somatic cell counts (SCC) of 9,220 cow milk samples of four different herds [2]. In their study, 7.8% of the cows had over one million cells/ml. Aasmäe et al. examined quarter milk samples having more than 400,000 cells/ml [3]. Udder pathogens were isolated from about one half of 157 samples from 30 farms. Tilga and Raid and Klaassen et al. did not specify sampling procedures. As the criteria for mastitis were different in the studies, the results are not comparable with each other. The sizes of the herds involved were not specified, nor were the criteria for the selection of individual animals. The milk received by the dairy plant concerned in this study was classified in three quality categories in 1998: A/ superior class with less than 415,000 cells/ml, B/first class with less than 521,000 cells/ml, and C/second class with less than 770,000 cells/ml. In 1998 the monthly average of superior-class milk delivered by the farms amounted to 96.3% with a variation range of 90.7%–100.0% [4]. The dairy plant started a project to improve udder health and farm hygiene in all herds supplying milk to the plant in 1998. The plant had no information on the udder health situation at the farms, and therefore a survey was consid- ered necessary prior to the project. The dairy plant, processing 15 million litres of milk annually, is located in a typical Estonian farming area, about 25 km from Tartu. In addition to producing milk, the plant also produces yoghurt, cream, sour milk, "kefir" (sour milk) and "sme- tana" (thick sour cream). High-quality raw milk is essen- tial to the production of these dairy products. The aim of the present study was to investigate mastitis prevalence, milking procedures and management practices in order to find out which measures should be taken into account in further udder health work. Materials and methods Study design All farms (n = 25) producing milk for the dairy plant were selected for the study. The farms belonged to 12 owners. Between November 1998 and March 1999, a dairy advisor and a veterinarian collected quarter milk samples from all cows producing more than five litres of milk per day on one farm visit. Milk samples were collected from 3,166 cows. During the farm visit, the veterinarian filled in a questionnaire about milking procedures and manage- ment practices with the help of the farm managers. The questions concerned the breed and age of the herds, mean annual milk production, milking procedures, milking units/milker, installation year and maintenance of milk- ing machines, measurement of vacuum, milking claw size, type of cowshed, bedding type and manure handling. Sampling Sampling procedures and laboratory analyses were carried out as in a Finnish mastitis survey in 1995 [5,6]. Quarter milk samples were collected aseptically immediately before milking. The teat ends were cleaned with alcohol (70%) swabs and allowed to dry. The first few streams were discarded and the milk samples (about 5 ml) were collected in sterile 10 ml plastic tubes. Samples were immediately cooled and transported in cool bags to the Estonian National Veterinary Laboratories either in Tartu, Paide or Vöru. Another non-aseptic quarter milk sample of 40 ml was taken in a 40 ml plastic tube for SCC counts from each quarter. The samples were cooled and trans- ported to the laboratory of the Institute of Animal Hus- bandry at the Estonian Agricultural University in Tartu. Analysis of milk samples The SCC values of 12,328 quarter milk samples were measured by using the Fossomatic Milko Scan System 215 (Foss Electric, Hillerod, Denmark). A quarter was consid- ered to have mastitis when the SCC was ≥ 200,000 [7,8]. Both subclinical and clinical cases are included in the results. To get a true average SCC of the farms, a value weighted by milk production was calculated from the ana- lysed quarter milk samples by multiplying the average SCC of each cow by its milk production and then dividing the average results by the total milk production of each farm. Microbiological analyses were carried out by streaking out 10 µl of milk with a sterile calibrated plastic loop on Tryp- ticase Soy Agar plates (BBL, Cockeysville, MD, USA) con- taining 5% bovine blood. The plates were incubated at 37 ± 1°C for 48 hours. The plates were observed for bacterial growth after an incubation period of 24 and 48 hours. Bacterial species were identified according to Honkanen- Buzalski and Seuna [9]. Data analyses The association of milking procedures and management practices with mastitis prevalence and the prevalence of bacterial pathogens (listed in table 1) was analysed statis- tically at herd level. The prevalence of mastitis and the prevalence of each bacteria species in the herds were used Page 2 of 6 (page number not for citation purposes)