ESTIMATION OF INTERDEPENDENCE AMONG QUARTERS OF THE BOVINE UDDER WITHSUBCLINICAL MASTITIS AND IMPLICATIONS FOR ANALYSIS

Interdependency among udder quarters with subclinical mastitis was eva luated on 150 farms using a total of 35,828 udder quarters. The occurr ence of high somatic cell count (SCC) (>250,000 cells/ml) in 0, 3, and 4 quarters occurred at a higher rate than would be expected based on independence of the quarters. For all bacterial species, intramammary infection in 0, 2, 3, or 4 quarters of the same cow occurred at a high er rate than would be expected based on independence of the quarters. Intramammary infection and high SCC were found less often in front qua rters than in rear quarters. High SCC and intramammary infection occur red more often in right front quarters than in left front quarters. Hi gh SCC in diagonal quarters occurred at a lower rate than expected. Co rynebacterium bovis, Streptococcus agalactiae, and Staphylococcus aure us had the highest intraclass correlation within herd. Streptococcus u beris had a very low intraclass correlation within herd. The intraclas s correlation within cow for the natural logarithm of SCC was 0.47. Co rynebacterium bovis and Strep. agalactiae had the highest intraclass c orrelation within cow, and Streptococcus dysgalactiae had the lowest. Analytical methods were proposed to manage the problem of interdepende nce and its effect on the design or evaluation of field studies on sub clinical mastitis.