1Department of Clinical Sciences, Faculty of Veterinary Medicine, Islamic Azad
University of Karadj, Karadj, Iran
2Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tehran,
Mammary secretions of 913 quarters from 229 pregnant Holstein heifers were obtained aseptically to determine the prevalence of coagulase-negative Staphylococci isolated during periparturient period. Quarter samples were collected 14 to 10 days before expected parturition. Analysis of culture data indicated that 78.5% (717/913) of samples were negative, 20.5% (187/913) contained coagulase-negative Staphylococci, 0.33% coagulase-positive Staphylococci, 0.33% E. coli, 0.22% Arcanobacterium pyogenes and 0.11% environmental Streptococci spp. A total of 187 isolates of coagulase-negative Staphylococci were tested in vitro for susceptibility to 8 antimicrobial agents. Susceptibility was detected in 180 (96.3%), 187 (100%), 163 (87.2%), 168 (89.8%), 183 (97.9%), 187 (100%), 174 (93%) and 164 (87.7%) isolates for oxytetracycline, gentamicin, streptomycin, tylosin, cloxacillin, enrofluxacin, trimethoprim+ sulphamethoxazole and penicillin G, respectively. More than 93.8% of the isolates were susceptible to all antimicrobial agents tested. In conclusion, results of this study suggest that coagulase-negative Staphylococci spp. is the most prevalent microorganism isolated from intramammary secretions in pregnant heifers which issusceptible to common antibiotics in vitro.