Leukosis product innovation at Lactanet: a new test and an integrated and optimized screening approach
- February 5, 2025
Bovine leukosis is an incurable disease affecting the health, productivity and profitability of dairies. A cow infected with the bovine leukosis virus generates an average of 635 CAD/year less than an uninfected cow (Kuczewski et al., 2019). About 90% of Canadian herds have at least one infected cow, but many herds actually have a significant proportion infected infected cattle (Kuczewski et al., 2019; Nekouei et al., 2015).
Given the large number of herds affected and the significant impacts of this disease, it is crucial to implement screening and control measures. The goal is to gradually reduce the presence of this disease in Canadian herds, an ambitious and necessary project for the prosperity of the dairy industry. One of the first steps is to identify the infected animals in the herd in order to, for example, isolate or cull them as they pose a risk to healthy animals
A new leukosis test
In collaboration with the Chair in Biosecurity at the Université de Montréal’s Faculté de médecine vétérinaire, Lactanet has validated a new test that will soon be available for the detection of leukosis in individual cows. And, from now on, this test will be the leukosis test offered at Lactanet.
It uses ELISA technology to detect antibodies against the bovine leukemia virus (BLV), which tells us if a cow has been exposed to the virus. Since the disease cannot be cured a cow with a positive ELISA test is considered to be actively, chronically infected.
For its validation, this new ELISA test was compared to other available leukosis tests (qPCR and lymphocyte count on blood samples). The results of this comparison demonstrate that the ELISA test is very efficient and reliable, with a better ability to detect positive cows, and an ability to confirm negative cows equivalent to that of other tests. The interpretation of the test has been optimized to further maximize its ability to detect negative cows.
It is important to understand that screening tests are not perfect. This is partly due to the dynamic nature of diseases, meaning that a disease develops over time and in a slightly different manner in each animal— every individual is different. That is why we validate and optimize the tests offered at Lactanet, and for their intended use (milk screening). In addition, as tests evolve, we revalidate and adjust them to ensure their best effectiveness and reliability.
A single interpretation threshold, with only two possible interpretations of the results: either negative or positive. Cattle will no longer be marked as “suspect”.
Benefits of the new ELISA test:
- Improved screening: maximized detection of negative cows and very good ability to detect infected cows, in addition to having minimized false-positive results.
- Practical use: no inconclusive (or “suspect”) results that leave uncertainty and make it difficult to manage and make decisions.
The phenomenon of carryover in milk recording samples
To fully validate this new test, it was important to evaluate the possible effects of residual milk, i.e. the risk of obtaining a false positive due to the contamination of the milk sample by the milk of the milked cow just before. This is because milk carryover from one positive cow to the next cow in the milking order can affect test results, “contaminate” the sample, and affect the milk recording test results. Obviously, this situation cannot occur when the sample is taken manually.
In the worst-case scenario, if the transfer of residual milk is not well-controlled during milk recording, the test will be less accurate when a healthy cow is milked right after an infected cow. This loss of accuracy leads to an increased risk of false-positive results, which are healthy cows that will be falsely identified as positive by the test.
To avoid false positives in leukosis screening results, here are some recommended best practices:
- Control of residual milk: Optimize sampling and milking equipment to reduce residual milk after each milking and to avoid contamination between samples. Consult your equipment dealer and your Lactanet technician for further advice.
- Sampling order: Whenever possible, sample cows starting with those that are least likely to be infected (young cows) to those that are most likely to be infected (known positive status, older cows, clinical suspicions, etc.).
- Confirmation with a manually collected milk sample (“hand-strip”): Before taking any action for a cow that has tested positive (such as culling), confirm her status with a milk sample collected manually and send it along with your next test, or use one of the other available tests.
- Integrated approach to making decisions for positive cows: Using the new national leukosis reports to make informed decisions (see next section of the article).
Integrated screening approach at Lactanet
With the validation of the new leukosis test, the Lactanet Leukosis reports have been redesigned to transform the product into more than just a regular health test. It is now a comprehensive management and decision support tool.
The Leukosis test offered at Lactanet is designed to be a screening tool used to detect the disease and monitor its evolution in herds. Thus, as with other herd tests offered at Lactanet, a Herd Summary Report has been developed with a test history to illustrate the herd’s status and to facilitate monitoring over time.
The Cow Summary Report has also been completely reimagined to incorporate milk recording and health test data. This new version of the report not only displays the test results but also assesses the impact of the disease on the productivity and health of cows that test positive. This allows for the identification of the most affected positive cows, enabling better-informed decisions based on their overall performance rather than just a single test result.
New National Leukosis Reports
Example of the new Leukosis Report – Individual Results
Example of the new Leukosis Report – Herd Summary
Conclusion
In summary, soon Lactanet will offer a complete solution for the detection and management of bovine leukosis, with reliable testing and integrating milk recording data to facilitate decision-making and improve the health and productivity of dairy herds. It is a practical, effective, and affordable approach, but above all, it is a unique and innovative Lactanet solution.
References
Kuczewski, A., Hogeveen, H., Orsel, K., Wolf, R., Thompson, J., Spackman, E., & van der Meer, F. (2019). Economic evaluation of 4 bovine leukemia virus control strategies for Alberta dairy farms. Journal of Dairy Science, 102(3), 2578-2592. https://doi.org/10.3168/jds.2018-15341
Nekouei, O., VanLeeuwen, J., Sanchez, J., Kelton, D., Tiwari, A., & Keefe, G. (2015). Herd-level risk factors for infection with bovine leukemia virus in Canadian dairy herds. Preventive Veterinary Medicine, 119(3-4), 105-113. https://doi.org/10.1016/j.prevetmed.2015.02.025
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The Lactanet Leukosis Individual Cow Test offers a comprehensive solution for leukosis detection and management.
