Editor’s note: This is the second of a three-part series. Click here to read the first article. I wrote in the first part of this series that it is important for the dairyman to first find out what he’s fighting and then work with the herd veterinarian on the treatment. By knowing what is causing the mastitis on their farm, the dairyman and their herd veterinarian are able to use the appropriate antimicrobial drugs. Armed with this knowledge, they may see a decrease in the total treatment duration or a reduction in the use of unnecessary broad-spectrum antimicrobials.

CEO / Lancaster Dairy Herd Improvement Association

The veterinarian plays a central role in the daily life of the dairy farm. Whether they are stopping by for a routine checkup or racing over for an emergency situation, it is important for them to work very closely with their local dairy farmers to ensure their animals are receiving the very best in veterinary care.

Part of the central role of the veterinarian is the judicious use of antimicrobials in the treatment of mastitis.

Whenever an animal or human host is exposed to an antimicrobial, there will be some degree of selection for a resistant bacterial population.

This process, known as mutational resistance, develops as a result of spontaneous mutation within the bacterial DNA that controls its susceptibility to a given antimicrobial.


After time, the presence of the drug serves as a selecting mechanism to suppress susceptible microorganisms and aid in the promotion of bacteria that have became resistant (mutational resistance).

Therefore, it is vital to limit therapeutic antimicrobial use in animals to those situations where the appropriate antibiotic is used to treat the appropriate bacteria.

This process is achieved through regular and close veterinarian involvement – where they assist producers by providing informed advice and guidance on the judicious use of antimicrobials.

I recently asked one of the vets that uses our lab for her opinion about the role of DNA mastitis sampling in her masitits testing and treatment program. Joy Lenker of Sunbury Animal Hospital in Sunbury, Pennsylvania, said:

“DNA mastitis sampling has given producers and veterinarians an opportunity to specifically identify pathogens associated with clinical and subclinical mastitis.

With greater emphasis on quality milk bonuses, it is important for our clients to know exactly what pathogens they are combating against, as well as producing the greatest-quality product for the consumer.

“Our practice uses this new technology in both preventative and treatment protocols. For preventative purposes, we recommend automatically checking cows with somatic cell counts (SCC) greater than 1,000,000 on monthly testing schedules.

This is usually done automatically by Lancaster County DHIA technicians after their monthly testing. This allows producers to identify problem cows very quickly and allows for rapid diagnosis and treatment.

The PCR technology also helps us identify what types of pathogens are present on the farm (i.e. contagious versus environmental pathogens).

“With emphasis on treatment, we are able to identify pathogens even if producers have already treated quarters.

So many times, clients will use the ‘shotgun’ treatment approach for treating mastitis and then would call for help when it was not effective.

Prior to PCR, we would have no choice, but to wait approximately three weeks until the antibiotics were gone in order to culture the pathogen. And in most cases, in three weeks, the cow is either dead or self-cured.

Since the PCR actually is testing for DNA, this is a super alternative to quickly find our causative agent and hopefully being able to resolve her mastitis in a quick and efficient manner.”

A dairy cattle veterinarian should have strong clinical evidence of the identity of the organism causing mastitis – based on clinical signs, history, laboratory data and past experience – before making a recommendation for antimicrobial use.

In addition, they should periodically monitor herd pathogen susceptibility and therapeutic response to detect changes in microbial susceptibility and to re-evaluate their antimicrobial selections.

Susceptibility testing is a tremendous adjunct to the DNA- based test for mastitis, as it serves as a guide for the practitioner that an antimicrobial should be effective in therapy.

Periodic susceptibility testing can provide historical data on which to base future empirical treatment as well as assist in selecting a treatment for refractory infections.

It is important to remember that only the cows produce the income on a dairy farm – it is all the milk in the bulk tank, not the per-cow average, that pays the bills.

Everything and everyone else is an expense or part of the overhead costs of running the farm. One way to keep cows producing quality milk is through the use of a herd health program.

Herd health programs are a form of preventative medicine which can include vaccinations, parasite control, reproductive/nutritional programs and mastitis control.

A cow that gets sick or has mastitis must be detected, separated form the herd, diagnosed and treated appropriately.

Through DNA-based mastitis testing and periodic susceptibility testing, it becomes easier for the veterinarian and dairy farmer to detect the cows not performing well, correcting their problem accurately and quickly, which leads to better herd health. PD

References omitted due to space but are available upon request. e to email an editor.

Lancaster DHIA has been using PCR-based asssays on milk samples since October 2010.