Whenever you have a clinical mastitis case, you have a choice about how best to help the cow with her problem. It has been a standard recommendation for many years that clinical mastitis cases should be treated promptly. Many streptococcal and staphylococcal infections will respond to antibiotic treatment. Treatment will help these cows. However coliform mastitis does not respond well to antibiotics. Since many clinical cases are caused by coliforms, maybe you shouldn’t treat these. If you have a mastitis diagnostic service conveniently available to you, you can find out the type of organism that is causing the problem and make a treatment decision.

Treat them all

The most common strategy in many herds is to initiate intramammary therapy on all clinical mastitis cases. This will not harm milder coliform cases although there is only weak evidence that it will help. More severe clinical coliform cases should be treated with systemic antibiotics. Many of these severe cases are at risk of the organism moving into the blood stream and systemic antibiotics could help these cows in a potentially life threatening situation. A high percentage of clinical mastitis may be due to streptococci and antibiotic therapy does have a good chance of being cost effective for these cows. Treating these cases may result in complete cures, and at the very least it will lower somatic cells, bacterial shedding, and reduce recurring flare-ups. Treating all your clinical cases with intramammary antibiotics may well make you money, even though it incurs a higher risk of having an antibiotic residue problem.

Don’t treat any

Not treating any clinical cows with antibiotics has been implemented and evaluated on many dairy farms throughout the country. It is true that on a lot of dairies today, most clinical mastitis is caused by coliforms. Most coliform mastitis cows will “get better on their own”; few are likely to die without antibiotics. Dairymen like the peace of mind of not having antibiotic residues risk and very small hospital groups. However, not treating the streptococcal infections is a bad idea. The long-term consequence of not treating strep cows is that the bacteria counts, and somatic cell counts on these cows will go higher, and these cows will flare up more.

Selective treating

A very simplistic view of the bacteria world is to divide them into two very large categories: gram positive and gram negative. The gram positive bacteria include organisms such as the streptococci and staphylococci. Cows with gram positive infections are likely to respond to intramammary antibiotic therapy. The gram negative organisms include coliform organisms such as E. coli and Klebsiella. The gram negative organisms are not likely to benefit from intramammary antibiotics. The standard bacteria culture will determine if organisms in a milk sample from a mastitis cow are gram positive or gram negative. If you could have even this much information for each clinical mastitis case within 24 hours, you can implement a very specific therapy strategy that will allow you to focus antibiotic therapy efforts on the cows that need it.

With a selective treatment plan it would always be prudent to initiate systemic antibiotic and supportive therapy on severe clinical mastitis immediately. The difference is that in this plan you would not start intramammary therapy. The gram positive / gram negative test is run to help you decide if intramammary treatment is a good idea. On the second day if you get gram positive growth, then you would start a course of intramammary treatment for only those cows.

The TNT Testing

The TNT test is a simple on farm test plate that narrowly focuses on this gram positive / gram negative question. The test culture plate has two chambers with two types of selective growth media. One side only lets gram positive organisms grow, the other side will grow only gram negative organisms. It is expected that an infection in a mastitis quarter will be caused by just one organism. So a positive culture growth should only occur on one side of the plate.

Step 1. Sample: Obtain a milk sample for culture from the problem quarter of clinical
mastitis cow.
Step 2. Set up: The milk sample is streaked onto both sides of the plate with a cotton-
tipped swab. The sample is then placed in a 37oC incubator overnight.
Step 3. Read: Examine the plate for growth of bacteria colonies the next day

This test guides us in the simple treatment decision "Should I start intramammary therapy on this cow”? If growth occurs only on the Red side, the bacteria is a gram positive organism, and you should treat the cow. If there is growth only on the Pink side, the bacteria is a gram negative organism, and you should not treat the cow. Another possible finding is that there is no growth on either side from a culture of a clinical mastitis sample. One of the most likely explanations for this is that the cow is successfully managing a coliform infection and she has already suppressed the bacteria growth in the quarter. No intramammary therapy is indicated for this case either.

Still Need the Name

There is still an undeniable benefit in knowing the name of the organism that is causing the mastitis. Sometimes culture will tell us that antibiotics are not the answer or should not be used. Infections from chronic Staph aureus do not respond well to antibiotic therapy and in most cases they are not worth treating. Yeast infections definitely should not be treated with antibiotics. The therapy decision is not always the most important question that needs to be answered. Knowing the name of the organism will lead you to specific prevention strategies that are much more important than the best treatment decision on any single case of mastitis. Mycoplasma organisms will not grow on either side of the TNT plate. If you run a TNT test on a clinical mycoplasma mastitis case you may correctly decide not to treat her, but the critical prevention strategy for Mycoplasma is to cull these cows. Implementing the correct prevention strategy will have a much bigger impact on your bottom line. So a sample should still be submitted to a mastitis diagnostic service to do a diagnostic culture. If the laboratory service is close by and you can get overnight results, you can have the best of both worlds: help with the treatment decision and information on the type of mastitis to guide your prevention efforts. The mastitis history of a cow also needs to be considered in the treatment decision. A certain percentage of your clinical mastitis cases will be repeat cases. Some chronic recurring clinical cases should not be treated at all. It is a smart move to sit down with your veterinarian and periodically review your treatment and laboratory records to fine tune the effectiveness of your overall mastitis control program.