Over the past 30 years the prevalence of bovine leukemia virus (BLV) infection has increased in North America, including Atlantic Canada, at both the herd and individual cow levels. This has occurred despite increased awareness of the disease and its deleterious effects and in the face of management practices aimed at reducing disease transmission.
Our objective was to identify risk factors associated with the within-herd prevalence of BLV-infected cows. We hypothesized that, as well as previously established risk factors, management practices associated with calf rearing and fly control would affect within-herd BLV prevalence.
A risk assessment and management program questionnaire (RAMP-Q) was developed and distributed to all bovine veterinarians in Atlantic Canada. All dairy farms shipping milk and who had bulk tank milk (BTM) samples collected in January and April 2017 (n=605) were eligible to participate in the RAMP-Q. BTM samples were tested with ELISA for levels of anti-BLV antibodies to estimate within-herd prevalence. RAMP-Q results were combined with demographic information collected from each farm and with the mean BTM ELISA results. Multivariable linear regression was performed to investigate the association between RAMP-Q risk factors and within-herd prevalence of BLV infection.
One hundred RAMP-Qs were returned, with participants from each province in Atlantic Canada (New Brunswick, 22; Newfoundland, 3; Nova Scotia, 49; Prince Edward Island, 26). Factors significantly associated with increasing level of within-herd BLV prevalence included history of clinical BLV within the herd (23.7% increase; 95% CI 6.8-39.9%) and history of purchasing BLV-suspect cattle (19.0% increase; 95% CI 3.4-37.0%). No significant difference in within-herd prevalence was associated with needle and injection (P-value 0.69), fly control (P-value 0.56), or rectal sleeve practices (P-value 0.48), or the use of bulls for natural breeding (P-value 0.81).
Important factors associated with increasing within-herd BLV prevalence include a history of prior diagnosis of clinical BLV and history of purchasing cows of unknown BLV status. In this study, there was no significant association of any previously established risk factors with increasing within-herd prevalence of BLV infection.
Resident, Large Animal Internal Medicine
Atlantic Veterinary College
I completed a Bachelors of Science in Microbiology at the University of Victoria before moving to Saskatoon and obtaining my DVM at the Western College of Veterinary Medicine. After finishing a rotating internship in large animal medicine and surgery at the Ontario Veterinary College, I began my residency in Large Animal Internal Medicine at the Atlantic Veterinary College. I am currently in my final year of the residency program while concurrently pursuing research in veterinary epidemiology, on surveillance and control of bovine leukemia virus in Atlantic Canada.
Thursday, June 14
10:30 AM – 10:45 AM
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