Mastitis represents a major economic challenge for dairy farmers. Additionally, it’s no secret that antibiotic usage in food animals is a hot-button issue with consumers. For dairy cattle, mastitis treatment represents an avenue of antibiotic usage.

Adherence to mandated milk and meat withdrawal specifications and rigorous product testing ensure product safety and quality, but methods to reduce usage and increase efficacy should also be sought.

In order to reduce use and increase treatment effectiveness, many dairy farmers have turned to on-farm milk culturing for mastitis pathogen identification. Using on-farm culturing after identifying a case of clinical mastitis allows for pathogen identification within 24 hours.

Using these methods, an ideal treatment regimen can be implemented on a case-by-case basis. This increases treatment efficacy, reduces lost milk, decreases drug costs, can decrease discarded milk and reduce antibiotic use by as much as 50 percent.

Despite the benefits of on-farm culturing, it is not widely practiced by dairies. Frequently, obtaining consistent and reliable culture results for meaningful management decisions is a challenge on dairy farms.

John Jacobs of Green Valley Dairy LLC, uses on-farm culturing on his dairy in Krakow, Wisconsin, and spoke about his experiences at the 2016 National Mastitis Council meeting. Green Valley Dairy LLC, currently milks around 3,000 cows and uses cultures to drive treatment decisions.

Jacobs obtained resources from the University of Minnesota (Minnesota Easy Culture System II) and received hands-on training from veterinarians at a milk quality lab after deciding to implement on-farm culturing at Green Valley Dairy.

After seven years of using on-farm milk culturing, Jacobs indicates milk culturing to be a learning process. “Like many things, we failed before we succeeded to implement on-farm culturing. Through trial and error, we learned that devoting resources and time was necessary to succeed,” Jacobs said.

Farms seeking to effectively implement on-farm culturing should devote the resources and time to setting up their labs and acquiring the proper materials. Green Valley Dairy has devoted a space and a technician, doubling as their calf specialist, to their laboratory.

Their lab space was retrofitted with a sink and running water, cabinets, countertops (with an easily sanitized surface), a refrigerator devoted to samples, a compact incubator, a microscope, bacteria identification charts and their culturing supplies.

Interpretation of on-farm culturing results can be challenging, with a steep learning curve. Keeping countertops and equipment clean and maintaining aseptic sampling and plating techniques are essential to identifying causative pathogens. Cultures sometimes return with contamination from improper sampling or lab techniques.

Bacteria on teat skin, the udder or on milkers’ hands can contaminate culture plates and confound culture results. Contamination can be avoided through strict adherence to approved milk sampling and culturing methods. Keeping lab spaces clean and procedures simple ensures successful implementation of milk culturing.

Standard operating procedures, data management and steps to executing meaningful managerial actions are also important. Protocols for identifying mastitis cases, milk sample collection, lab sanitation, milk culturing lab methods, organism identification, recording and reporting and equipment care and inspection are required for effective milk culturing, Jacobs said.

He uses the information derived from the lab for preventing the spread of contagious mastitis by establishing milking groups and orders and for culling decisions and vaccinations.

“The lab results have further aided us in reduced use of antibiotics,” Jacobs said.

Culture results help improve treatment and aid in management decisions as well. Many gram-negative bacteria (e.g., Escherichia coli, Enterobacter, etc.) are unresponsive to antibiotic therapy and treatment is not prudent. In these cases, focusing on the treatment of symptoms (e.g., fever, pain, etc.) is often the best course of action.

Some gram-positive bacteria (e.g., Strep. agalactiae, Strep. dysgalactiae, Strep. uberis, and coagulase-negative Staph.) are generally more responsive to treatment than gram-negative organisms.

Other gram-positive bacteria (such as Staph. aureus or Mycoplasma bovis) manifest themselves differently in the mammary gland and are harder to eliminate through antibiotic intervention.

In the case of known contagious pathogens (Strep. agalactiae, Staph. aureus, and Mycoplasma bovis), risk of infecting herdmates is greater. For this reason, making the decision to treat, cull, segregate, dry off the quarter or dry off the cow can prevent risk of infecting others.

This highlights the importance of data management in milk culturing, especially following treatment. Cows unresponsive to treatment, those with recurring infections or those infected with contagious organisms, should be managed differently than cows with transient or minor organisms.

A frequent concern with clinical mastitis cultures are those resulting in no growth on culturing media. Many producers believe this to be an error in sampling or lab methods, but this is not the case. Many mastitis cases result in clinical symptoms with no apparent causative agent. This can be caused by several factors.

One such factor is the point in infection. The manifestation of clinical signs results from a cow’s immune response, which in the case of “no growth” would indicate the cow has mounted an immune response and eliminated the pathogenic challenge. In a case like this, treatment would be unnecessary.

Another cause would be the pathogen is not actively shedding at the time of sampling, and subsequent cultures will need to be performed if symptoms persist or recur. Finally, if samples are not mixed before plating on culture media, bacteria can settle and not be picked up by the swab. This can be avoided by mixing tubes thoroughly before plating on media.

In addition to milk culturing, parlor towels, calf tubers, maternity milk buckets, calf bottles and pasteurized milk samples are regularly tested for bacterial contamination at Green Valley Dairy LLC. The lab isn’t strictly used for cultures, either.

The on-farm lab has enabled them to implement additional quality control measures on their farm. The technician also performs tests on SCC, milk and calf IgG, milk residue and bedding samples.

Even with on-farm culturing, communicating with lab specialists can also be important for unusual or questionable results. Green Valley Dairy frequently uses an outside lab for quality control verification and for advice on questionable results.

“The work may seem tedious, but the process pays off if you stay with it,” Jacobs said.

Producers interested in implementing mastitis culturing on their farms are encouraged to consult with extension specialists in order to develop a plan, obtain materials and establish standard operating procedures.  PD

PHOTO: Green Valley Dairy has devoted space and a technician, doubling as their calf specialist, to their laboratory. Their lab space was retrofitted with a sink and running water, cabinets, countertops (with an easily sanitized surface), a refrigerator devoted to samples, a compact incubator, a microscope, bacteria identification charts and their culturing supplies. Photo provided by John Jacobs.

Matthew Borchers is a graduate student at the University of Kentucky