Effectiveness of the California Mastitis Test as a Measurement of the Leucocyte Content of Quarter Samples of Milk

Abstract

Results obtained from 5,885 quarter-milk samples from 226 individual cows indicate that the most valid method of interpreting the California Mastitis Test (CMT) score in relationship to the leucocyte count is to score the CMT as positive or negative only. Interpreting all quarter-milk samples with a CMT score of zero as containing less than 500,000 leucocytes per milliliter yields a correct interpretation 89.9% of the time. Conversely, if all quarter-milk samples with a CMT score of 1, 2, or 3 are interpreted to contain over 500,000 leucocytes per milliliter, the interpretation will be correct 83.8% of the time. Individually, the CMT scores of 1, 2, and 3 will agree with the predicted leucocyte count only 56.7, 48.9, and 66.3% of the times, respectively. The logarithmic average leucocyte counts for the CMT scores of 0, 1, 2, and 3 were 99,770; 1,119,000; 2,951,000, and 9,750,000 per milliliter, respectively. The over-all logarithmic average leucocyte count for all 5,885 samples was 343,600 per milliliter. © 1967, American Dairy Science Association. All rights reserved.