Variation in Modified California Mastitis Test Scores in Dairy Cattle

Statistical analysis of coded modified C.M.T. scores, recorded over a 3-yr period from cows in 40 herds in two areas of Ontario, showed that an average of 22% of the within-herd variation in the scores was associated with variation in age of cow, stage of lactation, month of the year, and monthly production level. Age of cow was responsible for the greater portion of this and accounted for an average of 18% of the variation left after that due to the three other variables had been removed. The remaining three variables accounted for an average of 5.6% of the variation remaining after that due to age had been removed.