Haemophilus somnus infection: A retrospective analysis of cattle necropsied at the Western College of Veterinary Medicine from 1970 to 1990.

Results of necropsy examinations of 297 bovine carcasses with naturally occurring disease caused by Haemophilus somnus infection, and necropsied at the Western College of Veterinary Medicine in the period from 1970 to 1990, were analyzed with reference to the ages of affected cattle, seasonal occurrence of disease, the relative frequency of encephalitis, pneumonia, and myocarditis, and interrelationships among these conditions. The cattle came from 177 separate herds in the province of Saskatchewan. There was a range in age from one week to 10 years, and a mean age of 38 weeks. The diseases had a marked seasonal fall and winter incidence. The data indicated a trend characterized by an increasing percentage of cattle with pneumonia and myocarditis and a decreasing percentage with encephalitis during the period.