An Epidemic of Necrotic Bronchopneumonia Caused by Mannheimia haemolytica Serotype 6 on a Dairy Farm

Abstract

Eighty-seven (31%) of 290 cows suffered severe pneumonia on a dairy farm in Iwate Prefecture in March 2005. Thirteen of 17 deceased cows were in the early lactating period and were housed in a shed with free stalls. Pathological and etiological examinations of four dead animals revealed necrotic bronchopneumonia with Mannheimia haemolytica antigen as well as interstitial emphysema and syncytium formation in the lungs. M. haemolytica serotype 6 was isolated from the pulmonary lesions and bovine respiratory syncytial (BRS) virus gene was detected by PCR from the nasal swabs. A significant increase in serum antibody titers against M. haemolytica and BRS virus was found in other affected cows during the epidemic. These results suggest that feeding in loose housing systems and BRS virus infection could have been linked with the outbreak of the disease.