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Fifty Ohio dairy farms selected by stratified random sample were monitored to determine the incidence rate of clinical mastitis and prevalence of intramammary infection with the major intramammary pathogens. Population parameters for clinical mastitis incidence rate were estimated as 2.19, 3.33 and 4.36 cases per 100 cow-months at risk for herds with less than 50 cows, herds with 50–99 cows, and herds with more than 99 cows, respectively. The most common isolates from clinical cases were coagulase-negative staphylococci and Escherichia coli, each present in 14.6% of samples taken. Estimates of population prevalence of intramammary infection for Ohio dairy farms were: coagulase-positive staphylococci, 2%; coagulase-negative staphylococci, 2%; E. coli, 1%; other coliforms, 1%; Streptococcus agalactiae, 2%; esculin-positive streptococci, 5%; other esculin-negative streptococci, 3%. |
