Milk Quality and Mastitis Tests

A variety of diagnostic tests are routinely used to evaluate milk quality on dairy farms. Tests such as bulk milk bacterial counts, bulk tank somatic cell count and tests for adulterants such as water, sediment or antibiotics are routinely used by regulatory agencies. Other tests such as individual cow somatic cell count values, Staphylococcus aureus milk antibody tests, the California Mastitis test, milk conductivity and milk microbiology are often used diagnostically to investigate milk quality problems. Veterinarians also use various types of antibiotic susceptibility tests to help guide mastitis treatment decisions. The successful use of milk quality and mastitis tests requires knowledge of the methodology and diagnostic capabilities of each test. This paper reviews practical applications and supporting research of tests that are commonly used to investigate and solve milk quality and mastitis problems on dairy farms. Introduction Mastitis is usually considered the most costly disease of dairy cattle. Subclinical mastitis is considered the most economically important type of mastitis because of long term effects on total milk yields. Production losses due to subclinical mastitis were recently estimated to cost the dairy industry $1 billion dollars annually. Additional costs of mastitis are due to the failure to receive quality premiums from milk purchasers. While premiums vary regionally, the monthly premium opportunity for a select group of 54 Wisconsin dairy farmers was reported to range from $6.70 to $15.02 per cow per month (depending upon processor and current SCC level). More losses can be attributed to clinical mastitis, the risk of antibiotic residue violations, culling and death. Mastitis remains a concern of most dairy farmers and their veterinarians due to these profound economic consequences. Numerous diagnostic tests are used to test milk. Some tests are used to define raw milk quality. These tests include bulk tank somatic cell count (SCC), bacterial counts (such as the standard plate count (SPC)) and tests for adulterants such as water or antibiotics. Other tests are used diagnostically to investigate milk quality problems. Diagnostic tests include individual cow SCC values, the California Mastitis Test (CMT), milk conductivity, and milk microbiology. Other tests, such as antimicrobial susceptibility tests are used to guide treatment decisions. This paper will review the procedures and diagnostic capabilities of milk quality and mastitis tests and highlight the practical application of these tests for dairy farm problem