There are many different approaches to treating clinical mastitis on dairy farms. Some farms treat every clinical case with antibiotic tubes and supportive care. Other farms might not use any antibiotics on clinical mastitis, rather just supportive care when necessary. Yet others may only use antibiotics on severe cases of mastitis.
No matter the category your dairy falls in, it is important to track and record each case of clinical mastitis whether she is treated, not treated, or culled. The typical on-farm goal for clinical mastitis cases per year is less than 25% of the herd affected.
CULTURE CLINICAL CASES
When a cow is identified with clinical mastitis, consider a different approach other than blindly following the protocol of treat or no treat. Culturing clinical mastitis prior to treatment is simple, yields quick results, and helps to allow the producer to make a more informed decision.
Setup for on-farm culture is fairly easy and inexpensive. An incubator can range in price from $300-400 for very small, base models. A styrofoam egg incubator can also work, and is considerably less expensive. Other necessary items are culture plates (bi-plates are the easiest, other plates are available), sterile milk collection vials, and sterile swabs. Milkers can be trained to collect sterile milk samples and refrigerate after a new case is identified. The last and most important aspect of a successful on-farm culture lab is to identify a person who is interested and provides leadership and oversight to the program.
The simplest plate to use is a bi-plate. The bi-plate has two sides. Blood agar is the media where most aerobic bacteria will grow and Mackonkey agar only supports growth of gram-negative bacteria such as coliforms. After the sample is collected, trained personnel transfer a small amount of milk to the culture plate and incubate for 24 hours.
At that point, the plate can be interpreted to determine the result:
- No growth - the bacteria that caused mastitis has been cleared by the cow and antibiotic therapy is not indicated
- Gram-negative - antibiotic therapy is not warranted as the cow is typically able to clear the bacterial infection, however, the cow may need supportive care if necessary
- Gram-positive - typically Strep or Staph; intramammary antibiotic therapy is typically indicated
- Contaminated sample - these cows should either be re-cultured or not treated with antibiotics
REDUCE ANTIBIOTIC USE
The goals of implementing an on-farm milk culture lab are to reduce antibiotic use to only the cows whose cultured bacterial growth indicates they need it (gram positive) and to identify the common causes of clinical mastitis that are occurring on the farm so that appropriate intervention to reduce clinical mastitis can be enacted. The typical distribution of coliform, gram positive, and no growth should be approximately 33% in each category. That means that only about 33% of the cases of clinical mastitis (gram-positive) on a dairy farm will need antibiotic therapy.
While the milk of cows infected with gram positive bacteria typically becomes normal again after 5-6 days, those bacteria are the ones that can create chronic infections, causing increases in bulk tank somatic cell count. This is why these infections need antibiotic therapy early in the disease course.
Your veterinarian can help provide oversight and set up protocols for the on-farm milk culture program. Keep in mind that the decision to treat or not to treat is only in reference to antibiotics. Your veterinarian can write protocols for the supportive care that a cow might need depending on her physical condition.
Becoming proficient in reading culture plates also takes some practice. The easiest way to check your work is to send pictures of the plates to someone who can help, such as your veterinarian. At that point they can determine if additional testing may be needed on the plate, such as confirmation of contagious bacteria like Staph aureus or other bacteria such as Klebsiella. When you confirm your bacterial diagnosis, be sure to record your results.
Make an informed decision when treating clinical mastitis. The results will not only help reduce antibiotic use and save money, they will also help the entire herd by giving an epidemiologic snapshot of current clinical mastitis challenges.
For a video on how to culture a milk sample, click here.