Bovine leukemia virus (BLV) is a production-limiting disease common in North American dairy herds. To make evidence-based recommendations to Canadian dairy producers and their consultants regarding cost and financial benefits of BLV on-farm control, an economic model that takes the supply-managed milk quota system into account is necessary. Albertaspecific input variables were used for the presented analysis. A decision tree model program was used to evaluate economic aspects of decreasing a 40% BLV within-herd prevalence on dairy farms by implementing various control strategies over 10 yr. Investigated strategies were (1) all management strategies, including 3 options for colostrum management; (2) some management strategies; (3) test and cull; and (4) test and segregate. Each of these strategies was compared with a no control on-farm approach. The prevalence for this no-control approach was assumed to stay constant over time. Each control strategy incurred specific yearly cost and yielded yearly decreases in prevalence, thereby affecting yearly partial net revenue. Infection with BLV was assumed to decrease milk production, decrease cow longevity, and increase condemnation of carcasses at slaughter from cattle with enzootic bovine leukosis, thereby decreasing net revenue. Cows infected with BLV generated a yearly mean partial net revenue of Can$7,641, whereas noninfected cows generated Can$8,276. Mean cost for the control strategies ranged from Can$193 to Can$847 per animal over 10 yr in a 146-animal herd. Net benefits of controlling BLV on farm, as compared with not controlling BLV, per cow in a 146-animal herd over a 10-yr period for each strategy was: Can$1,315 for all management strategies (freezer); Can$1,243 for all management strategies (pasteurizer); Can$785 for all management strategies (powdered colostrum); Can$1,028 for some management strategies; Can$1,592 for test and cull; and Can$1,594 for test and segregate. Consequently, on-farm BLV control was financially beneficial. Even though negative net benefits were possible and expected for some iterations, our sensitivity analysis highlighted the overall robustness of our model. In summary, this model provided evidence that Canadian dairy farmers should be encouraged to control BLV on their farm.

Although Canadian dairy herds have been infected with bovine leukemia virus (BLV) for years, recent research has put new emphasis on the potential negative effects of this infection. Consequently, BLV control is becoming more favorable; however, BLV control cannot be successful without identifying infected animals. Bovicheck BLV (Biovet, Saint-Hyacinthe, QC, Canada) is currently the only assay licensed by the Canadian Centre for Veterinary Biologics. The first goal of this study was, therefore, to determine the reproducibility of the Bovicheck BLV assay for serum samples derived from Canadian cattle. The second goal was to evaluate and compare 5 different ELISA and determine their test characteristics using serum samples from Canadian herds. The considered ELISA were Bovicheck BLV, ID Screen BLV Competition (IDvet, Grabels, France), Idexx Leukosis Serum X2 Ab Test (Idexx Europe B.V., Hoofddorp, the Netherlands), Svanovir BLV gp51-Ab (Svanova, Uppsala, Sweden), and the Serelisa BLV Ab Mono Indirect (Synbiotics, Lyon, France). Eighty serum samples from Canadian cattle provided by Prairie Diagnostic Services (PDS; Saskatoon, SK, Canada) and an additional 80 serum samples from Canadian dairy and beef herds were used for the study. The Bovicheck BLV assay yielded the same results for all PDS-derived samples, implying a high level of reproducibility and robustness of this assay. Additionally, the comparison of the assays' results showed high agreement between assays, with Cohen's kappa values between κ = 0.91 and κ = 1. Furthermore, using original test results of the field samples as true status, relative diagnostic sensitivity and specificity were calculated. Relative diagnostic sensitivity of all tests was 100%. False-positive results were probable; therefore, the following relative diagnostic specificities were determined: 100% for Bovicheck BLV, Idexx Leukosis Serum X2, and Svanovir BLV; 95% for ID Screen BLV; and 97% for Serelisa BLV. When considering other test characteristics, ID Screen BLV is exceptional due to considerable practical advantages.

Bovine leukemia virus (BLV) infection, endemic in North American dairy herds, has production-limiting effects. A literature review of available papers published since 1995 concerning BLV transmission and its control was conducted. Although confirmed transmission routes were reviewed (blood, natural breeding, in utero, colostrum, and milk), there is still a lack of detailed information on other specific risks for transmission (e.g., contact transmission and hoof-trimming knives). Eradication of BLV has been achieved by combined management, segregation, and culling approaches. In contrast, although sole implementation of best management practices aimed at prevention of BLV transmission has decreased within-herd BLV prevalence, it has not eradicated BLV from a herd. Therefore, control and eradication of BLV by best management practices only should be further investigated. Additionally, the role of proviral load in infected cattle was investigated. Cattle with a high proviral load seem to be more likely to infect others, whereas those with a very low proviral load seem to have low risks of transmitting BLV. Information on proviral load could be taken into account when controlling BLV in high-prevalence herds. In conclusion, there is a need for detailed, large-scale studies investigating roles of specific transmission routes, knowing proviral load of infected individuals.

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