This article was written by Dr. Lisa Sharko.
The California Mastitis Test (CMT) is a rapid, on-farm screening tool used to detect mastitis in lactating ruminants by estimating the number of somatic cells in the milk. It is a cost-effective test that can be performed quickly by producers, providing immediate results. The CMT can be used to evaluate individual animals or to screen larger production groups, such as fresh does.
While the test is simple to perform, accurate interpretation requires training and experience. Producers are encouraged to work with their herd veterinarian to review testing techniques, develop a testing strategy, and establish response protocols based on test results.
CMT kits are available through veterinary clinics and agricultural supply retailers that carry animal husbandry equipment. Kits typically include a testing paddle, reagent, and manufacturer instructions for use in cattle.
The CMT reagent contains the detergent sodium lauryl sulfate (SLS), which lyses somatic cells in the milk and reacts with cellular DNA to form a gel. The degree of gel formation is directly related to the number of somatic cells in the milk. Milk with elevated somatic cells quickly forms a thick gel. The reagent also contains the pH indicator bromocresol purple. Elevated somatic cell concentrations are associated with increased milk alkalinity (higher pH), causing the milk-reagent mixture to appear darker purple compared to normal milk.
For use in goats, the reagent should be diluted at a ratio of 4:1 to 5:1 (4 to 5 parts water to 1 part reagent). This differs from the dilution commonly used in cattle milk (7:1 to 9:1). The more concentrated solution improves the ability to detect reactions in goat milk.
When to Use the CMT
A CMT may be useful in the following situations:
- When milk or udder abnormalities are observed.
- Four to six weeks following mastitis treatment to assess treatment success.
- During periods of elevated herd somatic cell counts (SCC) to support management and culling decisions.
- When screening groups of animals at critical management points, including:
- Fresh goats within three weeks of kidding.
- Prior to breeding.
- Approximately two weeks before dry-off to help guide selective dry-off treatment decisions.
The following instruction document can be used as a guide for performing and evaluating the California Mastitis Test on-farm.
