DISTRIBUTION OF CLINICAL MASTITIS AMONG QUARTERS OF THE BOVINE UDDER

Clinical mastitis episodes occurring from 1962 through 1991 in the Lou isiana State University Dairy Research Herd were studied to determine the distribution of clinical mastitis among quarters of the udder. Dat a were detailed records of all mastitis episodes that occurred during 1630 Holstein lactations. Incidence of episodes, categorized according to which quarters within a cow were clinical for a given case, were c ompared with mathematical expectations based upon the assumption that quarters were independent. Results indicated that quarters within a co w were more alike with respect to clinical mastitis than would be expe cted if quarters were independent. More episodes occurred in which eit her no quarters or all four quarters were clinical. Deviation of obser ved frequencies from expectation could have resulted from generalized cow differences, such as cow milk yield, immune competency, mammary ty pe characteristics, and general health. Front quarters had less clinic al mastitis than rear quarters when all episodes were considered. No d ifference was observed in incidence between front and rear quarters wh en only first episodes in first lactations were considered. No differe nce was observed between incidence in left and right quarters. Diagona l pairs occurred less often than expected and at about half the freque ncy of other pairs. Dependence between quarters should be taken into c onsideration when experiments are designed and analyzed.