AABP Executive Director Dr. Fred Gingrich is joined by Dr. Justine Britten, a PhD animal scientist working at Udder Health Systems Inc. This episode is brought to you by the AABP Milk Quality and Udder Health Committee. AABP members with an interest in milk quality are invited to volunteer to serve on the committee. Find out more information about the committee by visiting this page.   

Staph aureus is a contagious mastitis pathogen and Britten states that every dairy is affected to some degree by Staph aureus with a huge range in severity and prevalence between herds. Veterinarians play a key role in developing monitoring and prevention programs. Culturing remains a key point in identifying animals that are affected with Staph aureus so they can be evaluated for culling, segregation or treatment. Cultures should focus not only on clinical animals because Staph aureus is commonly a subclinical infection. It is estimated that 2-15% of heifers will freshen with the infection and their somatic cell count may be low for some time before it begins to climb. Treatment should be reserved for heifers and it is critical to identify it early in the course of infection to increase chance of treatment success. 

Britten states that in most circumstances, there is no need to do sensitivity testing on milk cultures unless there is an outbreak situation with apparent treatment failures. Bulk tank cultures are important and a minimum for routine herd mastitis monitoring. The sensitivity of bulk tank cultures is low but serial positive silos from a dairy indicate a higher prevalence of the infection up to 5-10% of the cows.  

We also discuss that in outbreak situations it is important to evaluate why cows are getting infected and remember that cows typically get infected in the parlor and focus efforts there. This includes evaluating teat condition, parlor procedures and equipment function. Aggressive culturing programs, segregation and culling are important to minimize risk.  

Britten provides these three take-home points for veterinarians:

Take-home point #1 – Not all Staph aureus colonies exhibit beta-hemolysis, therefore, it is important that all Staph colonies undergo coagulase testing to identify Staph aureus.

Take-home point #2 – Monthly bulk tank cultures are a bare minimum monitoring program for dairy farms.

Take-home point #3 – Somatic cell count is a lagging indicator and cultures will detect infections earlier.

Mastitis is the number one disease of dairy cattle and should be involved in milk quality and mastitis prevention programs. The Milk Quality and Udder Health Committee has developed guidelines for milk quality service providers. Find this document under the Committee Resources page, click on the Milk Quality and Udder Health page, then the Committee Resources tab to find these documents.