Mastitis pathogens and antibiotic resistance in beef cows in Switzerland

Mastitis in beef cows has not been studied as extensively as mastitis in dairy cows, and data from Switzerland are lacking. Various studies have shown a similar pathogen spectrum as in dairy cows, which could not be confirmed in this study. To gather initial data from Switzerland, milk samples from 297 lactating beef cows from 31 herds from the Engadin Valley in the Canton of Grisons were examined bacteriologically. At least one major or minor mastitis pathogen was recovered from at least one individual-quarter or composite sample from 33 % of all cows. The most common major mastitis pathogens were Staphylococcus aureus (8,4 % of cows), Pasteurella multocida (4,1 %), Streptococcus uberis (2 %) and Streptococcus dysgalactiae (1,7 %). Sixteen percent of the cows had at least one blind quarter, but only 32 % of these had been previously detected by the owners. In the second part of the study, milk samples from beef cows with mastitis were examined bacteriologically; the cows originated from various parts of Switzerland and had been presented for veterinary treatment. Pasteurella multocida (22 %) and Staphylococcus aureus (21 %) were the most common pathogens isolated. Antibiograms using microtitration and disk diffusion testing were generated for the Staphylococcus aureus, Pasteurella multocida and Streptococcus uberis strains from both parts of the study. Fifty-six percent of the Staphylococcus aureus strains were resistant to penicillin G. Our results showed that bacteriological examination of a milk sample aids in the diagnosis and allows specific treatment of mastitis in beef cows; this may be further improved with antibacterial susceptibility testing. Our preliminary data for the resistance patterns of mastitis pathogens in beef cows will facilitate evidence-based treatment strategies.