Does it really make a difference which coagulase-negative staphylococcus (CNS) species infects cows in your herd? Research published in the May Journal of Dairy Science says it does.

Researchers in Belgium tested monthly milk samples from 25 cows in three herds as well as samples from clinical mastitis cases over a 13-month period to determine which pathogens were most prevalent and caused the most intramammary infections. Not surprisingly, they found the distribution of the causative pathogen was highly herd-dependent. Overall, Staphylococcus chromogenes, Staphylococcus xylosus, Staphylococcus cohnii, and Staphylococcus simulans were the most prevalent. Interestingly, no CNS species were found to cause clinical mastitis.

The scientists note that that Staph. chromogenes, Staph. simulans, and Staph. xylosus induced an increase in somatic cell count that is comparable with that of Staphylococcus aureus. Almost all CNS species were able to cause persistent mastitis infections, with Staph. chromogenes causing the most persistent infections.

Therefore, they conclude that as a group, CNS should still be considered as minor pathogens, but special attention should be given to the previously listed species because of their impact on somatic cell count. Because of this, accurate species identification cannot be ignored since the effect on somatic cell count differs between species and species distribution is herd-specific. And, they add, further study would be helpful to develop cost-benefit analyses for management changes and, if needed, treatment recommendations.