University of Minnesota

Dairy Initiatives

Dairy

Department of Animal Science


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Reducing Mastitis by
Counting Bugs

RALPH FARNSWORTH and RUSSELL BEY
College of Veterinary Medicine, University of Minnesota

Environmental mastitis due to non-ag strep and coliforms has become the major mastitis problem in many herds, thanks to widespread efforts to control contagious mastitis and other management changes.

Procedures such as J5 vaccination and vitamin E selenium supplementation can help increase cows' immunity, but reducing exposure to disease organisms is still the best way to prevent new infections.

We know from experiments that the more organisms present on the teat skin when the milking machine is applied, the higher the new infection rate. We also know that if the numbers of organisms on the teat are reduced, the new infection rate drops rapidly.

Environmental mastitis does not normally spread from cow to cow. Although this may be possible, it's probably rare. For all practical purposes, the exposure is from the environment.

Keep Cows Clean and Dry
One simple recommendation for control of environmental mastitis is to milk clean, dry cows. This is a noble goal, but what is clean? And dry? What is really required is to milk cows with few bacteria on the teat skin. A cow that looks "clean and dry" probably has a lower number of bacteria on the teat skin than does a cow with manure on the teats -- but is it low enough? There is also a problem with the definition of clean. What is clean to one person may not be to another.

Be Consistent
Another issue is consistency. Every teat needs to have a low bacteria load every milking to effectively prevent infections. Dairy producers frequently adapt a cow prep procedure that has been shown to reduce bacteria and assume that as a result they have reduced bacteria. However, even a proven procedure will not work if not done consistently and correctly. For example, teat ends are frequently missed.

Monitor Milkers
Milker training and compliance with established procedure is critical. Monitoring milker performance by watching occasionally does not assure consistency. Videotapes can show if a procedure is being followed, but they won't show enough detail to let you evaluate quality of cow prep. To assure consistency, train milkers well and monitor them on a continuing basis.

Monitor Milk
Culturing bulk tank or inline samples to accurately determine the numbers of non-ag strep and coliforms is an accurate, sensitive, and reasonably easy to use way of assessing the bacterial load on teat surfaces. Remember: The milking machine is a great teat-washing machine. What milkers fail to remove before machine attachment will end up in the milk.

Diagnose and Fix Problems
When you find that the bacterial load is too high, the next step is to determine the reason. Bacterial load is the result of two factors: the number of bacteria that get on the teat between milkings (from stalls and other environmental areas) and the number removed by the cow prep procedure. Both of these need to be controlled. If the cows are excessively dirty, no amount of cow prep can be completely successful. On the other hand, even though cows appear clean, it is unlikely the bacteria load will be low enough that cleaning is not needed.


Proper Bulk Tank/Milk Line Collection

Bulk tank cultures and in-line milk sample cultures can help you assess factors such as milking practices and bedding management as well as the level of contagious organisms in the herd. But for the results to be meaningful, you must collect and handle the samples correctly. Some words of advice:

  • Collect bulk tank samples from the top of the bulk milk tank after adequately agitating it. If you're sampling a bottom-loading tank, drain the milk down to the clean-out door and take the sample. Do not sample from the outlet valve because bacteria can grow around the valve.
  • When collecting line samples, be sure to sanitize and rinse the collection vessel and tube before sampling. Keep the collection vessel cold at all times to prevent bacterial growth. If you take a subsample for laboratory analysis, mix the primary collection vessel first. Freeze or cool the sample immediately and keep it cold or frozen.
  • Make sure the bulk tank has been properly cleaned, not merely hosed out.
  • A good rule of thumb is to do monthly bulk tank analysis. On some herds it may be preferable to conduct the analysis more frequently. In large herds twice a month is not unreasonable. This will help you detect problems before they become bigger and more costly.
  • Have a high-quality laboratory do the analysis. In general, you get what you pay for.

D A I R Y    I n i t i a t i v e s    N E W S L E T T E R
Volume 10    Issue 3    Fall 2001