ASSOCIATION BETWEEN PREVIOUS 305-DAY MILK-YIELD DISEASE IN NEW-YORK-STATE DAIRY-COWS

Logistic regression was used to examine the association between milk y ield and disease. We studied 8070 cows of second or higher parity from 25 New York State Holstein herds, calving between June 1990 and Novem ber 1993. Previous 305-d mature equivalent milk yield was used because most of the disorders studied occurred too early in lactation for cur rent milk yield to be considered. Seven disorders were studied: retain ed placenta, metritis, ovarian cyst, milk fever, ketosis, abomasal dis placement, and mastitis. A separate model was used for each disorder. Each model included, in addition to milk yield, parity, calving season , and herd. Results showed that higher milk yield was not a risk facto r for any disease except mastitis. However, the association between hi gher previous milk yield and mastitis does not necessarily imply causa tion.