JAVMA • Vol 250 • No. 10 • May 15, 2017 1167 Ruminants T he North American bison industry has grown steadily in recent years. 1 According to the 2012 Census of Agriculture conducted by the USDA, 2 there are approximately 162,110 bison (Bison bison) on 2,564 private farms in the United States. In Can- ada, results of the 2011 Canadian Agricultural Cen- sus 3 indicate that there are 125,142 bison on 1,211 farms, most of which are primarily pasture-based operations. In 2011, 13,048 bison were slaughtered in Canada, a number that has increased over time. 4 The growing farmed bison industry has stimulated study of diseases that have adverse effects on bison production. Clinical presentation, prevalence, and risk factors associated with Mycoplasma bovis –associated disease in farmed bison (Bison bison) herds in western Canada Ana L. Bras DVM, MSC Herman W. Barkema DVM, PhD Murray R. Woodbury DVM, MSC Carl S. Ribble DVM, PhD Jose Perez-Casal PhD M. Claire Windeyer DVM, DVSC From the Departments of Production Animal Health (Bras, Barkema, Windeyer) and Ecosystem and Pub- lic Health (Ribble), Faculty of Veterinary Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada; the Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada (Woodbury); and Vaccine and Infectious Disease Or- ganization-International Vaccine Centre, University of Saskatchewan, SK S7N 5E3, Canada (Perez-Casal). Dr. Bras’ present address is Feedlot Health Management Services Ltd, 370181 79th St E, Okotoks, AB T1S 2A2, Canada. Address correspondence to Dr. Windeyer (c.windeyer@ ucalgary.ca). OBJECTIVE To describe the clinical presentation of Mycoplasma bovis –associated disease in farmed bison, determine the prevalence of farmed bison herds affected by M bovis –associated disease in western Canada, and evaluate the associa- tion of operation-specifc risk factors with M bovis –associated disease. DESIGN Cross-sectional survey. SAMPLE 202 bison producers in western Canada. PROCEDURES Members of the Canadian Bison Association in 2013 and 2014 who had farmed bison operations located in the provinces of Alberta, British Colum- bia, Manitoba, and Saskatchewan were contacted and asked to complete a telephone survey between June 2014 and February 2015. RESULTS Of the 441 eligible producers, 202 (46%) completed the survey. Twelve (6%) herds had a laboratory-confrmed diagnosis of M bovis –associated dis- ease in at least 1 bison. Among the affected herds, clinical presentation of the disease was frst noticed between May 2009 and January 2015 and per- sisted for a median of 12 weeks. Cows > 3 years old and yearlings were the animals most frequently affected and had a high case fatality risk. Factors positively associated with a herd being affected with M bovis –associated disease included being located in Alberta and large herd size. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that M bovis is associated with high morbidity and mortal- ity rates in farmed bison, affecting mostly cows > 3 years old and yearlings, particularly among large operations and those in Alberta. Mycoplasma bovis appears to be an emerging pathogen of farmed bison in western Canada and merits further investigation so that effective prevention and control strategies can be developed and implemented. ( J Am Vet Med Assoc 2017;250:1167–1175) Mycoplasma bovis is an emerging pathogen of North American bison. 5 The first anecdotal report of M bovis outbreaks in farmed bison was in 1999. 6 To date, 4 case reports 7–10 of M bovis outbreaks in bison have been published in which the pathogen has been associated with chronic pneumonia and polyarthritis in feedlot operations and high morbidity (character- ized by lameness, swollen joints, respiratory tract dis- ease, and lethargy) and mortality rates in cow-calf op- erations. To date, peer-reviewed reports that describe the epidemiology of M bovis–associated disease in farmed bison are lacking. Mycoplasma bovis–associated disease and con- trol measures in cattle have been described and re- viewed. 11,12 However, the characteristics of M bovis– associated disease in bison are distinctly different from those in cattle. Among bison, cows > 5 years old appear to be the animals most susceptible to dis- ease caused by M bovis, whereas among beef cattle, M bovis causes disease primarily in calves and young ABBREVIATIONS CBA Canadian Bison Association CFR Case fatality risk CI Confdence interval IQR Interquartile range (25th to 75th percentile)