Variation in Modified California Mastitis Test Scores in Dairy Cattle

Abstract

Statistical analysis of coded modified California Matitis Test scores, recorded over a 3-yr period from cows in 40 herds in 2 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. The coded modified C.M.T. scores were adjusted for effects of age of cow, month of year, stage of lactation, and monthly milk production within herds, and the adjusted values were subjected to a component analysis of variance within each of the 2 areas. Herd components of variance were 39% and 30%, years within herds 0%, cows within herd years 43% and 48%, and monthly tests within cows 18% and 21% for each of the 2 areas.