ASSOCIATION OF CHANGES IN THE BACTERIAL ECOLOGY OF BOVINE MASTITIS WITH CHANGES IN THE USE OF MILKING MACHINES AND ANTIBACTERIAL DRUGS

The results of mastitis bacteriology made by the National Veterinary a nd Food Research Institute in Finland during the past 50 years (1.15 m illion samples) are viewed in relation to simultaneous changes in dair y cow management. Although intensive preventive measures have been app lied for decades, the prevalence of bovine mastitis has not decreased. Instead, pathogenic bacteria are becoming progressively less suscepti ble to the available therapy. In part this must be due to the emergenc e of antibiotic resistant strains of bacteria, but it seems that the b acterial spectrum has also changed. The incidence of Streptococcus aga lactiae (group B streptococci) has decreased, while in contrast, the i ncidence of staphylococci, initially Staphylococcus aureus and later c oagulase-negative staphylococci, has increased. Results suggest that e xternal pressure, like changes in animal husbandry, including antimicr obial treatments and introduction of modern milking machines, act as s elective forces on the bacterial species which cause bovine mastitis.