Over the past dozen years, dairy producers have become accustomed to using DNA technology to speed genetic advancement and manage herd inventories. Now, DNA technology can help with quickly identifying mastitis pathogens.

Saltman roger
DVM / RLS Management Solutions LLC
Roger Saltman was formerly a Group Director for Cattle and Equine Technical Services with Pfizer...

New DNA-powered technology allows for more effective mastitis surveillance. On-farm or in-clinic polymerase chain reaction (PCR) tests can detect the presence of specific DNA markers for mastitis pathogens like prototheca, mycoplasma, strep and staph in a milk sample. These tests are quick and can provide same-day results, and samples can be pooled from up to five cows to save money.

Quick and accurate diagnosis

A quick diagnosis of subclinical and clinical mastitis cases is most important after freshening and through about 45 days in milk (DIM). This period is one of the two critical times when cows are most challenged by mastitis-causing pathogens.

Mastitis prevention in fresh cows really starts at dry-off, which is the other most critical period for mastitis control. In recent years, protocols have evolved at dry-off to incorporate selective dry cow therapy that allows producers to identify cows at highest risk of mastitis. These cows can receive antibiotic therapy coupled with a teat sealant to help protect the udder throughout the dry period. On-farm tests using DNA marker technology can help speed up the process to identify the presence of potential mastitis-causing pathogens at dry-off.

Cows at lower risk can just receive the teat sealant, which reduces the use of antibiotics and allows the cow to use her own immune system to fight off mastitis-causing pathogens.


With cows protected over the dry period, attention turns to prevention, diagnosis and treatment of mastitis cases at and shortly after freshening. Even with great dry cow protocols in place, cows can still freshen with mastitis. Cows can be affected by any number of different pathogens, so it’s important to diligently monitor fresh cows to catch mastitis cases quickly, diagnose the pathogen causing the infection and implement proactive treatment practices.

Consistent protocols

On large dairies, several cows calve each day, which makes surveillance more difficult without adequate and consistently followed routine fresh cow milk quality protocols. A fresh cow surveillance program using PCR technology may look something like this:

  • Once each week, all animals fresh from four to 10 days have a composite milk sample taken from all four quarters using National Mastitis Council-approved aseptic milk sampling protocols.
  • Five-cow pooled samples are created by taking equal amounts of each of the individual composite cow samples. The original cow samples are then refrigerated for future testing, if needed.
  • These five-cow pooled samples are tested for the presence of genetic material from mycoplasma and prototheca species using a PCR reagent specific to those organisms. Additionally, a separate and specific PCR test is applied to the pooled samples to determine presence of genetic material from Staph aureus and Strep uberis.

Results of the testing protocol can identify cows that test positive for the presence of DNA material associated with specific mastitis pathogens. Developed in concert with your veterinarian, protocols should be in place to manage these cows effectively. For cows that test positive for mycoplasma or prototheca DNA markers, the following protocols should be considered:

  • Move positive cows into a separate group and milk them last.
  • It’s possible some of these cows could be culled due to any number of factors including mastitis history, past performance, reproductive challenges and others. In this case, conduct a follow-up sample on the individual animal to confirm the presence of mastitis pathogens.
  • Alternatively, the screened animal could continue to be milked in the “chronic” pen and, if clinical mastitis becomes present, she could be immediately culled.

For cows that test positive for the presence of strep or staph DNA, early diagnosis is critical and can enhance cure rate. Antibiotic therapy designed to target specific organisms should be used as directed by the label and in accordance with protocols established by your herd veterinarian. Appropriate withhold times for meat and milk should be determined and followed.

Monitor success

Proper monitoring, diagnosis and treatment can help reduce clinical and subclinical mastitis incidents. Still, it’s important to monitor mastitis cases to determine if your monitoring and treatment protocols are working. A few data points can help identify the effectiveness of your program:

  • Clinical mastitis rate. What percent of cows show clinical signs of mastitis each month? What is the trend over the past six months? What is your goal? Trendlines can indicate if your process is effective in improving milk quality.
  • Fresh cow clinical mastitis. Diving deeper into your clinical mastitis rate, how much of this clinical mastitis occurs in the first 30 DIM?
  • Recurrence rate. What percent of mastitis cases happen again after treatment? If this number is high, you could have issues with environmental pathogens, your mastitis treatment protocols or both.

Remember that other factors have an impact on mastitis rate, including seasonality, age, barn type and other factors. Regardless of these variables, it’s important to remember: Mastitis cases early in lactation can have an additive effect on higher health costs and lower production in the current lactation and beyond. A standard process that allows for quick and accurate identification of mastitis pathogens, coupled with an effective treatment and monitoring program, will help get your cows off to a healthy start after calving and set them up for a productive and profitable lactation.