The prevalence of clinical and subclinical mastitis in dairy cows in the central region of Fars province, south of Iran

licensed dairy farms in the central region of Fars province were randomly selected in order to participate in aseasonal prevalence study. A cross-sectional study was designed to determine prevalence at cow and quarterlevel based on clinical signs for clinical mastitis and indirect tests for subclinical mastitis. 6180 quarters from1545 dairy cows were tested by clinical examination and California mastitis test (CMT). Milk samples fromboth clinical and subclinical quarters were collected for bacteriological culture. 4714 (76.28%) quarters werehealthy, 1335 (21.6%) quarters were positive by results of CMT (as indicated to subclinical mastitis), 44(0.71%) quarters showed clinical mastitis signs and 87 (1.41%) quarters were blind. The clinical and subclinical mastitis prevalence at cow level was 2.2 and 42.5%, respectively. There was no significantdifference in the prevalence of mastitis between different quarters, seasons and cities. The most prevalentisolated bacteria were coagulase positive staphylococci followed by Streptococci, Escherichia coli andcoagulase negative staphylococci. Insufficient control measures such as pre and post milking hygiene and dry cow therapy in dairy farms and limited knowledge of farmers on the importance, identification and control of mastitis, especially subclinical forms, can be the main causes for the high prevalence of mastitis in Farsprovince.