Risk factors for Mycoplasma bovis-associated disease in farmed bison (Bison bison) herds in western Canada: A case-control study

Abstract

North American bison producers have been attempting to control and prevent Mycoplasma bovis-associated disease without the benefit of bison-specific knowledge. The objective of this study was to determine the clinical presentation of disease associated with M. bovis infection in western Canadian farmed bison, and to identify herd-level risk factors for M. bovis-associated disease. Bison producers (n=49) from western Canada (Manitoba, Saskatchewan, Alberta, and British Columbia) were selected for a 1:2 case-control study. Data were collected by an in-person interview using a questionnaire regarding clinical presentations of outbreaks and herd-level management factors. Risk factors associated with M. bovis outbreaks were identified using multivariable logistic regression analysis. All 17 case herds had a laboratory-confirmed diagnosis of M. bovis infection within the last 5 years. In 11 (65%) of the 17 case herds, disease associated with M. bovis infection recurred in subsequent years. Overall, 88% of case herds had recently introduced bison that later developed clinical signs associated with M. bovis infection. Within a bison operation, a median of 8% (Inter Quartile Range [IQR]: 3-11%) developed clinical signs: lameness, reluctance to move, swollen joints, difficulty breathing, coughing, sluggishness, and loss of body condition. Also, calving percentage the year after the first M. bovis outbreak was lower than calving percentage the year before the outbreak. Herd-level mortality risk during the first M. bovis outbreak in case herds ranged from 0.5 to 50% (median 5%, IQR: 3-10%) and the median case fatality risk was 100%. Case herds were more likely than control herds to have a feedlot unit (OR=7), to receive regular visits from rental trailers or trailers from other farms (OR=15), to annually vaccinate bison (OR=7), and to lose at least one bison due to fatal respiratory disease in the previous year (OR=9). These findings will aid development of evidence-based recommendations for management to prevent and control Mycoplasma bovis in farmed bison in Western Canada.

Keywords: Farmed bison; Morbidity; Mortality; Mycoplasma bovis; Outbreak; Risk factors.