Highly contagious, both Staphylococcus aureus and Streptococcus agalactiae are considered major mastitis pathogens that can significantly impact dairy producers economically. For the most part, these pathogens cause subclinical intramammary infections that quite often become chronic, John Middleton of the University of Missouri told attendees at the National Mastitis Council regional meeting in Ghent, Belgium, held Aug. 4-6, 2014. Sometimes, though, they can be associated with a high incidence of clinical disease.

Mastitis remains the most costly problem in the dairy industry after decades of research with intense focus on management practices and the introduction of modern equipment. Published research reveals that one-third of all dairy cows are estimated to have mastitis and that 50 percent of cows in Canada and the U.S. have one or more infected quarters.