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Virginia Cooperative Extension - Knowledge for the CommonWealth

Raw milk bulk tank analysis.

Dairy Pipeline: July 2005

Alan G. Grove
Extension Area Dairy Agent
Valley of Virginia
(540) 564-3080 email:

For a producer struggling with milk quality or mastitis issues, a bulk tank analysis is a good starting point to pinpoint possible problem areas. A bulk tank analysis should not be used to replace quarter milk samples when attempting to solve a mastitis problem, the results will identify the predominant types of bacteria in the bulk tank. A bulk tank analysis includes a standard plate count (SPC), a preliminary incubation count (PI), a lab pasteurized count (LPC), a somatic cell count (SCC), and a bulk tank milk culture (BTM). A high SPC (>15,000) may indicate poor udder preparation or intramammary infections (mastitis). A high PI (>30,000) indicates improper sanitation of equipment or cows, dirty equipment or cows, or contaminated water. A high LPC (>200) indicates poor cleaning of equipment or bulk tank. A high SCC (>200,000) indicates mastitis and you should review milking procedures, improve sanitation of cattle housing areas, and check for proper equipment function. The BTM culture gives an actual count of the various species of bacteria present in milk. One of the best uses of BTM cultures is to indicate the presence of Staph. aureus, and Strep. ag., two indicators of mastitis. To ensure accurate results a proper sample must be taken from the bulk tank and delivered to the lab in a timely fashion (within 48 hours). The bulk tank should be agitated for at least 5 minutes (longer for larger tanks) and a sanitized dipper used to collect the sample. The sample should be refrigerated or kept on ice until delivered to the lab. Using these results, your veterinarian, field representative, or state inspector can then determine what steps to take to resolve the problem.

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