Relationship between California Mastitis Test Reaction and Production and Composition of Milk from Opposite Quarters

The relationship between the California Mastitis Test (CMT) reaction of milk from individual quarters and production was determined by comparing the production at a single milking, of opposite quarters of the same udder which differed in CMT reaction. Comparisons were obtained for 1,258 opposite-quarter milkings from 763 cows in 30 dairy herds. These oppositequarter comparisons were well distributed over the lactation period, season of year, and between front and rear halves of the udder. Test reactions (on total quarter milk) of trace, 1, 2, and 3 were associated with average decreases in milk production of 0.42 (9.0%), 0.95 (19.5%), 1.72 (31.8%), and 2..33 (43.4%) kg per quarter per day, respectively.