Routine diagnosis methods used in bovine mastitis were studied in 55 mares in lactation. The findings of strip cup test, California Mastitis Test-CMT, electronic somatic cell count-CCS, microbiological culture, and in vitro antimicrobial susceptibility profile of isolates were discussed. Streptococcus spp., Staphylococcus spp, and enterobacteria were the most common microorganisms isolated in health and CMT-positive mammary glands. Staphylococcus aureus and Arcanobacterium pyogenes were identified in two mares presenting clinical mastitis. Mean somatic cell count of eight mares without presence of microorganisms in milk was 247.57x10³/mL and 1.621,86x10³/mL in 47 mares with positive microbiological culture. Moderate concordance (63.8%) between positive reactions in CMT (1 to 3+) and microbiological culture was observed. Amicacin (78.9%), ceftiofur (74.7%), sulpha-trimetoprim (69,0%) and norfloxacin (69.0%), were the most effective drugs, while resistance of isolates was mainly observed against penicillin (64.8%), gentamycin (35.2%), azithromycin (35.2%), enrofloxacin (28.2%), and florfenicol (28.2%).

An uncommon outbreak of mastitis caused by Arcanobacterium pyogenes in 26 cows is reported. The epidemiological findings, clinical signs, microbiological exams, somatic cell count, in vitro susceptibility profile of strains, efficacy of intramammary treatment and control measures were discussed. Florfenicol (96.2%), cefoperazona (92.3%), cefaloxin (84.6%) and ceftiofur (84.6%) were the most effective antimicrobials, and neomicin (27.0%) and enrofloxacin (17.4%) the least effective antimicrobials.