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Virginia Cooperative Extension - Knowledge for the CommonWealth

Get a handle on sub-clinical mastitis

Dairy Pipeline: November 2004

Sue Puffenbarger
Extension Area Dairy Agent,
Franklin County
(540) 483-5161 email:

Did you know that for every case of clinical mastitis that you have in the herd, there are anywhere from 15 to 40 cases of sub-clinical mastitis? This can equate to an increase cost of $200/cow/year and be the cause of elevated Bulk Tank Somatic Cell Counts (BTSCC) and loss of monthly premiums. There are ways to help you manage this often overlooked problem. Two of the most effective ways are DHIA records and the California Mastitis Test or CMT (see October 2003, Dairy Pipeline). To determine who your chronic sub-clinical cows are, use the Milking Cow Somatic Cell Report that you receive monthly after test. Identify those cows that have a SCC greater than 400,000 for the current and previous test. Usually these are the cows at the top of the list, but not always. I suggest you go one step further and look at the lactation information for those cows. If you have PCDART, you can look at all lactations in one place on the Cow Page-Test Day tab (and do not have to go through lots of paper!). Sub-clinical cows will have multiple tests, not necessarily sequential tests, with SCC's greater than 400,000. These cows would be the ones to do a CMT on and identify problem quarters. The individual positive quarters should be sampled and sent off for laboratory analysis. One comment I receive often is "I sent some samples off and they came back with no growth!" One way to minimize this occurrence is to take multiple samples at different milkings. Some of these organisms are intermittent shedders and won't be found at one point in time. Take three or four aseptic samples, freeze them, send them off for analysis and make sure to ask the lab to pool samples for each cow. You greatly increase your chance of eliminating false negatives. By targeting these sub-clinical cows, you can identify whether you have an environmental problem (usually facilities related) or a contagious pathogen (Staph Aureus or Strep Ag). Work with your Veterinarian or Extension Agent to then develop a control program. By targeting these cows, you can greatly reduce your BTSCC and increase your chance of obtaining a monthly premium!

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