Mastitis is a universal problem that all dairy producers struggle with to varying degrees at one time or another. Management strategies to reduce the risk of mastitis usually focus on decreasing exposure of cows to the bacteria that infect the mammary gland. These strategies include practicing proper milking protocols, paying close attention to hygiene, maintaining clean free stall beds and corrals, and limiting introduction of infected animals to the herd. Tools have been developed to help dairy producers detect mastitis, and these have evolved over many decades from simple cow side tests to specialized DNA analyses. If you can’t measure it, you can’t manage it.
Few tools were available to monitor mastitis in the early days of dairy production. For individual cows, one relied on observation to find cows with abnormal milk or swollen quarters. By the time these clinical signs were obvious, infection was already well established. Early detection is valuable to identify infected animals so that effective treatment decisions can be made. The Standard Plate Count (SPC) was one of the first milk quality tests applied to measure total bacteria in milk. The SPC of commingled milk reflects hygienic conditions of milk harvest and storage, and also gives an indication of udder health status. In 1915, the SPC upper limit in California for raw milk was 200,000 cells/cc. This was reduced in the 1920’s and 30’s, and finally dropped to the current SPC limit of 50,000 cells/cc in 1970.
In the late 1950’s, a simple and inexpensive cow-side test called the California Mastitis Test (CMT) was developed by veterinarians at UC Davis . The CMT indirectly measures immune cells that travel to the mammary gland in response to an infection. With this test, dairymen could find cows with subclinical mastitis before visual signs developed. DHIA laboratories used the test to provide members with milk quality information in addition to monthly milk weights. The CMT ushered in a whole new era of milk quality management, and it continues to be widely used around the world.
In the 1970’s, technology for directly counting immune cells (also known as somatic cells) in milk became available. DHIA and other milk testing laboratories embraced this technology and replaced CMT reporting with more precise SCC information. In California, a regulatory threshold of 750,000 cell/ml SCC in bulk tank milk was adopted in 1970 (this was later reduced to 600,000 in 1990). In recent years, other on-farm tests for measuring SCC in milk have become available, including the Porta-SCC and the Delaval Cell Counter. Both the CMT and the SCC are measures of the cow’s own cells in milk that are present to fight an infection. Other tests are needed to determine the types of bacteria causing the infection.