The California mastitis test (CMT) serves as a fundamental screening tool for dairy farmers and veterinarians, providing a rapid assessment of somatic cell count in milk. This simple, low-cost procedure helps identify subclinical mastitis infections that otherwise remain hidden, allowing for timely intervention. By detecting abnormal milk composition, the test supports herd health management and milk quality preservation across operations of all sizes.
How the California Mastitis Test Works
The test relies on the interaction between a milk sample and a specific reagent, typically a surfactant solution, which causes visible changes in consistency. When combined with milk from a single quarter, the reagent reacts with DNA released from somatic cells, leading to a thickening or gel formation. The degree of thickening correlates with the somatic cell count, indicating the level of inflammation or infection present in that quarter.
Step-by-Step Procedure
Milk a small strip from each quarter into a clean, dry paddle or well plate.
Add an equal volume of the CMT reagent to each well.
Gently swirl the plate to mix, avoiding splashing or aeration.
Observe the mixture for immediate thickening, gel formation, or no change.
Record results based on a standardized scoring system, typically from 1 to 4.
Interpreting the Results
Results are commonly expressed as a numerical score, with higher numbers indicating higher somatic cell counts and greater likelihood of infection. A score of 1 suggests minimal cell content, while a score of 4 points to a severe inflammatory response. Consistent scoring and proper technique are essential to ensure reliable, comparable data over time.
Benefits for Herd Health Management
Regular use of the California mastitis test enables early detection of problematic quarters, often before visible symptoms appear. This proactive approach reduces the risk of antibiotic misuse, supports targeted treatment plans, and helps maintain bulk tank somatic cell count within regulatory limits. Over time, data trends inform culling decisions and improvements in milking hygiene.
Limitations and Best Practices
While the CMT is a valuable screening tool, it does not identify specific pathogens or differentiate between bacterial species. False positives can occur due to environmental contamination or recent milking, and false negatives may appear in the early stages of infection. To maximize accuracy, consistent technique, proper reagent storage, and routine equipment cleaning are essential.
