Progress report for LNC23-478
Project Information
The sustainability of the U.S. dairy industry is threatened by an increasing prevalence of bovine leukemia virus (BLV), now infecting almost all U.S. herds and almost half of U.S. dairy cows. BLV acts by interfering with the cow’s immune system, leaving animals with increased vulnerability to common cattle diseases and conditions. In addition to causing lymphoma, this retroviral cousin of HIV/AIDS has recently been recognized as reducing milk production, decreasing cow lifespan, decreasing vaccine efficiency, exacerbating heat stress, and increasing rates of mastitis and lameness. This epidemiologic puzzle has only been revealed in the last 15 years. Additionally, animal suffering and BLV-associated human mammary cancer are recent concerns shaking consumer confidence in dairy products.
Over 20 countries have eradicated BLV by simultaneously culling all infected cattle. This approach is economically impossible for the U.S. where almost half of the cows are infected. The recent development of a BLV qPCR assay determines the concentration of BLV provirus (PVL) in a blood sample. Animals with higher PVL can be thousands of times more infectious than herd mates with a lower PVL. We have recently shown on four pilot U.S. herds that BLV prevalence was dramatically decreased by removing only those cattle with the highest PVL (Figure 1 and 2).
The proposed project, “Demonstration of a new method to eliminate BLV from your dairy herd by targeting culling of the most infectious cattle” will recruit Organic Valley Cooperative membership farms to determine the ease and return on investment for our control method. We will enroll farms of different size, management style, and geographic location. Annually, all milking cows will be ELISA tested and positive animals will be assayed for PVL. Using PVL, the most infectious cows will be targeted for culling. Annual reports will monitor each herd’s new infection rate and average PVL.
Dissemination of project outcomes to producers, veterinarians, industry representatives, extension experts, and researchers will be a major component of project outcomes. We will encourage participating producers to share their experiences, outcomes, and successes in BLV control. The results of the project will be used for our many educational materials and programs.
The project will demonstrate to both organic and conventional dairy producers that BLV can now be effectively controlled without an economically catastrophic immediate culling of all infected animals. With their value-added products, Organic Valley Cooperative is well positioned to implement and advocate a new standard of BLV-free milk production.
We aim to inform the U.S. dairy industry about BLV’s economic impact and demonstrate a comparatively low-cost control program. Study outcomes include: (1) producers learning BLV control by targeted culling in their own herd with the potential for complete eradication; (2) participants gaining increased knowledge, awareness, and skills to control BLV; (3) creation and dissemination of educational materials and programs for expert and novice audiences; and (4) constructing a community with shared goals during the project and beyond. Production of BLV-free milk will decrease dairy production losses, improve animal welfare, remove human health concerns, and better compete with milk alternatives.
Recent research has shown that cattle infected with bovine leukemia virus (BLV) have diminished or weakened immune systems associated with reduced milk production, shortened cow lifespan, and lymphoma. We recently estimated annual losses between $300 and $400 per milking cow. While over 20 nations have eradicated BLV by culling serologic positive animals, the U.S. prevalence has grown to almost 50% so that simultaneous culling of all serologic positive animals is economically prohibitive. Recent findings show that a minority of cattle with high concentrations of provirus are responsible for most transmission. Culling the high proviral load (PVL) animals is a clear critical control point to stop the many direct and indirect routes of transmission. We have recently shown in four pilot herds that BLV can be controlled and eventually eradicated using a two-step testing program to cull or segregate high PVL cattle. We propose conducting a participatory demonstration and educational program to: (1) demonstrate how BLV can now be controlled, and (2) educate the agricultural community about BLV impact (herd and economic) and control programs.
BLV Impact: Bovine leukemia virus (BLV) reduces animal welfare. BLV infected animals have reduced milk production, decreased lifespan, decreased vaccine efficiency, exacerbated heat stress, and increased rates of mastitis and lameness. BLV acts by disrupting the animal’s immune system, and thereby enabling infection with numerous opportunistic pathogens.2-3 Three large studies have shown that herd milk production decreases as milk production increases. Survival analysis showed that BLV-infected cows had a 23% to 30% increase in culling as compared to their herdmates. If the cows are not sustainable then neither will be the farms. Animal prevalence of BLV in the U.S. has increased from approximately 10% in the 1970’s to almost 50% of all U.S. dairy cows and more than 30% of U.S. beef cows. Our MSU BLV Research and Extension team’s studies estimated annual BLV costs of ~$300 per milking cow for the average U.S. dairy herd.5,11-12 Estimates have indicated a $2.7 billion nationally deficit due to BLV infections.7 Acting through a wide variety of other diseases and conditions, the true costs of BLV are difficult to estimate. However, more recently, inclusive economic models have been published. Recent concerns of reported associations between BLV and human mammary cancer continue to challenge consumer perception of dairy and beef products. The demand for BLV-free animal protein may follow the path taken for cage-free poultry, pork
raised without farrowing crates, and organic foods. Many consumers may switch to animal-free protein that is manufactured, cultivated, fermented, or cultivated using tissue culture technologies. BLV will be one of the factors that make it more difficult for animal agriculture to be sustained when competing with a growing number of alternatives to the livestock industries. Over 20 nations have eradicated BLV by simultaneously culling all cattle with BLV antibodies. This approach would economically devastate most U.S. herds which would have to sell or cull about 50% of their milking and youngstock animals. Our team found that management interventions (single-use gloves and hypodermic needles) are only mildly effective. Until two years ago, extension experts, educators, and dairy specialists lacked a feasible recommendation for BLV control. The proposed project includes only dairy cattle. However, the project outputs will also benefit BLV control in the beef industry. In 2016, our team found a 39% BLV herd prevalence in Michigan beef herds.9 More recently, collaborators in Kansas estimated a 96% BLV herd prevalence and a 55% within herd prevalence.10The need for the beef industry to address BLV is clear, and control may require the same diagnostic assays and culling strategies as used for dairy.
BLV Diagnostic Assays: Historically, BLV infection status is determined by detecting BLV antibodies using an enzyme-linked immunosorbent assay (ELISA) on milk or blood samples. While identification of BLV antibodies is informative, the assay lacks the ability to indicate the level of BLV infection or provide a way to rank animals based on infectiousness. A quantitative polymerase chain reaction (qPCR) assay amplifies BLV provirus, or BLV that has been integrated into the host’s B-cells. Results from the BLV qPCR assay measures the number of viral copies per volume of blood, nasal secretions, saliva, milk, or other fluids, referred to as proviral load (PVL). The BLV ELISA lowly correlates with PVL (r=0.28) and differs vastly among ELISA-positive cattle. The first herd our MSU BLV Extension and Research team tested 12 years ago had 12 BLV ELISA cattle with PVL ranging from 30 to 48,826x104 copies per µL of blood. This means that the cow with the highest PVL had 1,648 times more provirus per volume of blood than the cow with the lowest PVL.26 Hence, the term “super shedder” is used for cattle with high PVL. We have shown that the many routes of BLV direct and indirect transmission primarily come from these super-shedders. Therefore, super-shedders are a clear critical control point for reducing transmission by culling or segregation from the rest of the herd. Besides being the most infectious, the highest PVL cows are most likely to experience the highest immune disruption. For other retroviruses such as HTLV and HIV, it is widely accepted that PVL is associated with infectivity. Proviral load assay for PVL demonstrates a similar association. No BLV transmission was found twenty months after 20 low PVL cows were introduced to a herd of 105 BLV ELISA-negative cattle. Additional work has tracked genetically distinct proviral clones based on genomic insertion sites and found that low PVL cattle rarely transmit BLV. Research from our team as well as others has found that quantification of PVL has merit for identifying cows with the highest risk of transmission.
BLV Pilot Studies: Our team has conducted pilot field trials in four herds in which targeted culling of high PVL cows was used to control BLV. The herd
prevalence decreased significantly for each of the first 3 herds, and their combined prevalence went from 62.0% to 20.7%. The last herd using this approach was a 3,000-cow herd which started with a 20% prevalence. Currently, the herd is taking the last steps toward eradication. The proposed project will further demonstrate that this new BLV control method is robust and effective on dairies with various management protocols. We will directly measure the costs of the control program for comparison with previously measured estimates of BLV economic impact. Importantly, we will prioritize producer and veterinarian discussions for BLV control, management, and culling or segregation decisions.
Outreach and Education: Generations of U.S. animal scientists and veterinarians have been teaching dairy producers that BLV is not a concern because it only causes lymphoma in a small percentage of older cattle. We now know that this was false. BLV has continued to squeeze its way to the forefront of conversations and concern. The proposed demonstration project will be the basis for our outreach and educational programs. Our long-term goal is to educate the agricultural community at large that BLV infection in U.S. cattle is costly and no longer needs to be tolerated.
Our Team: The Michigan State University (MSU) BLV Research and Extension team has been engaged with BLV focused research and education for over 13 years. Founded by Bartlett (cooperator) and currently led by Kendrick (project coordinator), the team aims to provide advanced scientific knowledge, improved educational resources, and beneficial consultation discussions for BLV management and control. Organic Valley Cooperative and membership farms focus on specialty dairy products and have the capacity to market milk separately produced by BLV-free herds. Membership producers have voiced an interest in controlling BLV and are excited to engage with the project by discussing their concerns and management strategies with the research team while implementing a BLV control program. CentralStar Cooperative has been a leader in BLV diagnostic assays, providing both a milk BLV ELISA and blood qPCR assay. The MSU BLV Research and Extension team has a strong 13-year collaboration with CentralStar, and together continue to advance BLV scientific knowledge and diagnostic assays.
Assumptions and Limitations: Our pilot studies indicate that the proposed demonstration project should have successful results among all dairy farm
environments. However, the organic dairy producers may experience a slower decrease in BLV prevalence due to current unknown factors. This project is the first to focus on BLV solely in organic dairy farms which have different management protocols than those of conventional dairy farms. Our limitations depend on participating producers and veterinarians actively culling targeted animals. However, personal, economic, or other influences may render the producer unwilling or unable to cull the high PVL cattle. We will monitor for culling of the highest PVL cows per herd. Discussions between the research team and participating producer will recommend culling decisions. Any producer unwilling or unable to cull or remove the agreed upon animals will be removed from the study, and a new replacement herd will be enrolled in the study, if possible.
Research
We hypothesize that with strategic testing and culling of the highest BLV PVL cows, herds will experience decreased herd BLV prevalence, decreased within herd BLV prevalence, decreased rate of new BLV infections, and overall increase economic gains. Additionally, with improved educational and outreach materials, participants and outreach attendees will have improved awareness, skills, and attitudes about BLV and BLV control programs.
We will conduct a participatory BLV testing program that measures and demonstrates the feasibility and associated costs of BLV eradication by identifying and removing cows with the highest infectious potential as measured by BLV PVL. We will disseminate knowledge obtained to educate the agricultural community. Producers will prioritize the culling of cows with the highest PVL and retain lowly infectious animals (low PVL). As the highest PVL cows are removed, producers will eventually find themselves culling cows with progressively lower PVL values until no cows with a measurable PVL remain. Based on our BLV pilot studies, the proposed BLV control program should reduce the rate of new BLV infections, herd average PVL, and overall BLV ELISA prevalence (measured study outcomes). Costs of control will be directly measured and compared with previous estimates of BLV economic impact. The proposed demonstration project will be the foundation for education and outreach outputs for the dairy community. We will publicize how it is now possible to reduce and eradicate BLV without the economic devastation of immediately culling all infected (ELISA-positive) animals.
We hypothesize that with strategic testing and culling of the highest BLV PVL cows, herds will experience decreased herd BLV prevalence, decreased within herd BLV prevalence, decreased rate of new BLV infections, and overall increase economic gains. Additionally, with improved educational and outreach materials, participants and outreach attendees will have improved awareness, skills, and attitudes about BLV and BLV control programs.
Selecting farms: Organic Valley Cooperative project cooperator veterinarians Hain and Jodarski have currently identified four organic dairy producers that are eager to begin addressing and learning about BLV control within their herds (see attached letters verifying participation). Approximately ten organic dairy producer and veterinarian pairs will be selected from the North Central Region (NCR) including Michigan, Wisconsin, Iowa, Minnesota and Indiana. Transparency, communication, and discussion will be stressed to all team members (including project coordinator, cooperators, and participating farms) for successful project progression, completion, and outputs.
DHIA milk testing: Dairy Herd Information Association (DHIA) is a national milk and component testing service available to almost all U.S. dairy farms. We estimate that about half of our selected farms will already be paying for DHIA service. However, we may need to pay for a minimal amount of DHIA testing. CentralStar Cooperative routinely obtains access to the DHIA records in collaboration with Dairy Records Management System (DRMS) and will allow us to track each cow’s milk production and presence in the herd. We will never ask that a specific animal be culled. However, as an indicator of culling effort, we will measure how many of the highest 7 PVL cows in each herd are being culled. Producers unwilling or unable to remove some high PVL cows will be replaced by other producers in subsequent years of the project.
BLV ELISA and PVL sample collection: CentralStar Cooperative Laboratories have a system in place with DHIA to receive and transport both milk and blood samples collected throughout the NCR-SARE region. To start the project, each participating farm will have their DHIA-collected milk samples tested for BLV antibodies (BLV ELISA) as evidence of infection. BLV ELISA-positive cows will have blood samples collected either by the participating producers or veterinarians and shipped overnight to CentralStar Cooperative for BLV PVL (BLV qPCR) testing. Project coordinator (Kendrick) and personnel at CentralStar Cooperative have experience in establishing mailing protocols, receiving samples, and BLV analysis to guarantee a smooth process for participating farms. When herd BLV PVL results are completed, a ranked list of animals by BLV PVL will be shared with the producers in a consultation discussion. Producers will then target cows with the highest PVL for culling or at least for temporary isolation until culling is possible. For example, cows targeted for culling may be temporarily segregated if they are in peak milk or about to calve. PVL action levels for removal from the herd will progressively decrease over time as cows with extremely high PVL values become increasingly rare. When low BLV herd prevalence is established, incoming heifers will also need to be tested for BLV.
The proposed BLV control program was piloted on four conventional dairy herds. It became clear that the most efficacious and economical protocol was for annual BLV ELISA screening of the milking herd with follow-up BLV PVL measurement on ELISA-positive animals.26 Rarely did we find that a cow’s PVL changed substantially within a year.
Sample size and anticipated results: The study endpoints will be the BLV herd ELISA prevalence and the reinfection rate (new infections per 100 cow-months at risk) calculated for each lactation and each herd. We have previously shown in three small herds and one large herd that culling animals with the highest BLV PVL can reduce BLV herd prevalence (Figure 1 and 2). These pilot projects are not yet sufficient to convince producers that the BLV control program should work on their farm and no field trials have been done on organic dairy farms. The BLV ELISA-prevalence for the three small herds experienced a decrease in BLV herd prevalence from 62% to 22% (Figure 1). The BLV ELISA for the large (3,000-cow) herd experienced a decrease in BLV herd prevalence from 20.8% to 0.85% (Figure 2). OpenEpi will be used to assess rates of new infections compared to rates in our other field studies using person-time comparison of rates with conditional maximum likelihood estimator (CMLE) rate ratios and mid-P exact p-values. Our proposed sample size of about 1,500 cows from approximately 10 organic dairy herds will be sufficient for statistical significance (P < 0.05) of the project outcomes. However, our experience is that statistical significance is insufficient to convince dairy producers. We therefore aim to determine the efficacy, cost and feasibility of the BLV control program in organic farms of various sizes, geographic locations, and management protocols.
Data retrieval and analysis: Participating producers will be required to update or revise their dairy management system to include both BLV ELISA and PVL results for each tested animal. CentralStar Cooperative also maintains a database with all DHIA and BLV testing information. Cooperator (Bartlett) will utilize the information in the farm’s dairy management system and CentralStar’s database to summarize and analyze each herd’s data. We will prepare an annual comprehensive report showing the herd’s past and current BLV ELISA prevalence, rate of new infections, and average BLV PVL. We will also prepare a figure showing the proportion of the herd’s total PVL that is coming from the highest PVL cows (Figure 4).
As a demonstration project focused on education and outreach, all project participants (producers, veterinarians, project coordinator and cooperators) will engage in creation, review, and dissemination of project outcomes. While it is unlikely that BLV will be eliminated in all participating herds in the three years of the project, reductions in animals with high PVLs should be extremely evident. Additionally, the gained awareness, knowledge, and the skills developed by participating producers will aid in continuing the BLV control program on the farm until the virus has been eliminated. Subsequent herd monitoring, eg. bulk tank testing, to confirm eradication will be informed by programs used in countries that have already eradicated this disease.
The cost to control BLV (testing, animal handling, culling, etc.) will be recorded on all herds and will be compared to the economic impact of BLV as estimated by our previous research. Labor costs for BLV ELISA testing will be zero since this task is completed by DHIA technicians as part of regular milk testing. Hours of labor and needed supplies will be estimated for blood collection. The cost of culling (dairy value minus slaughter value) will be estimated by the producer and multiplied by the herd manager’s assessment of what proportion of the reason for culling was due to a high BLV PVL.
Eradication: BLV ELISA and qPCR testing is equally available to farms of all sizes and management types. However, smaller farms will find it easier to eliminate BLV by culling the last infected cow. BLV-free herds are then typically monitored with periodic bulk tank milk ELISA testing. Several large U.S. dairy surveys have found that 5 to 10% of herds are totally BLV-free in spite of their neighboring herds being infected.1 Therefore, we believe that BLV-free herds can be maintained in the U.S.
Farmer involvement and confidentiality: The dairy producers will be active participants in the proposed demonstration project. The cooperators at Organic Valley will continue to identify participating farms among their clientele and membership (see letters verifying participation). The identity of individual farms will remain confidential for any form of project dissemination unless producer permission or requests are granted. We have found that seeing progress being made by other de-identified farms is an effective way to motivate dairy producers to prioritize BLV control and management.
Participating farms or any dairy farm will never be subject to bad publicity for having BLV-infected cattle. Almost all U.S. dairy farms have BLV, so there is no stigma involved in having infected cows. Also, BLV is not a USDA or state reportable disease. To date, our research team has run multiple field trials for many diseases and has never had our study participants’ confidentiality compromised. Producers starting the study with an exceptionally high BLV prevalence may request to delay releasing their results until their prevalence is reduced and the producer is comfortable acknowledging their current situation.
Compensation: Individuals collecting blood samples for the project will be compensated for overseeing the project aims and sample collection. Additionally, all materials and supplies for blood samples collection will be provided by the supported NCR-SARE proposal. Project coordinator (Kendrick) and/or cooperator (Bartlett or Durst) will visit each farm and discuss the project with the producer and veterinarian once in the first year and then as needed in year 2 and 3.
CentralStar involvement: CentralStar Cooperative has provided the BLV ELISA testing to their customers for over 15 years and has offered the BLV qPCR assay since they developed and validated it five years ago. Collaboratively, CentralStar Cooperative and the MSU Research and Extension team has processed over 50,000 samples for BLV testing over the last five years. Additionally, CentralStar Cooperative runs approximately 40,000 samples per year for producers addressing BLV on their own.
CentralStar Cooperative currently supplies several laboratories throughout U.S. with milk based BLV ELISA testing through DHIA, and therefore is in the optimal position to offer follow-up BLV PVL diagnostic testing for PVL which was developed in collaboration with the MSU BLV Extension and Research team’s pilot field trials...
Organic Valley Cooperative involvement: A project cooperator (Bartlett) has worked with Organic Valley Cooperative on a previous study including 60 farms regarding antimicrobial resistance. Bartlett has given two seminars to their membership regarding BLV and has had open communication with Organic Valley Cooperative for two years about the possibility of doing the proposed project.
Without the use of insecticides, organic dairy herds often find difficulty controlling BLV-transmitting biting flies on pasture. Therefore, organic dairy farms are especially interested in preventive measures that work with their farm management protocols. Even though organic dairy farms are typically a small fraction of the dairy market, they tend to “drive the discussion” regarding animal welfare, use of drugs, and using preventive medicine rather than curative medicine. Organic dairy farms tend to set the standards for chemicals and sustainable farming in the dairy market and are therefore well-positioned to advocate for BLV-free milk production.
In year 1, eight (8) farms located in WI, MI, and MN were enrolled in the project. Project cooperators were assigned as farm lead contacts and the whole milking herd was assessed for BLV prevalence. Farm information is provided in the table below:
| Farm | Approximate Herd Size | Percentage of Animals BLV ELISA-Positive | Number of Animals with high/moderate BLV PVL levels |
| 1 | 280 | 28% | 2 high PVL, 11 moderate PVL |
| 2 | 30 | 50% | all animals tested had low PVL |
| 3 | 130 | 52% | 1 high PVL, 13 moderate PVL |
| 4 | 50 | 57% | all animals tested had low PVL |
| 5 | 50 | 70% | 1 high PVL, 2 moderate PVL |
| 6 | 40 | 32% | all animals tested had low PVL |
| 7 | 70 | 25% | 3 high PVL, 2 moderate PVL |
| 8 | 600 | 34% | 83 high PVL, 21 moderate PVL |
Consultation reports were shared and discussed with producer and farm/veterinary teams. Fallowing the discussion, summary of the discussion and action items were shared with entire research team and farm teams. In year 1, action items in discussion were focused on: colostrum and milk feeding management, milking order, blood-to-blood transfer prevention, bulls used for live cover, and breeding BLV-positive females to beef. Example final report can be viewed here: https://drive.google.com/file/d/1Ac_sq5UceUIFF3hHmc9Hp5-mWUBEok_r/view?usp=sharing
In 2025, herds will be sampled again and consultation reports generated. Discussions will focus on changes implemented since 2024, changes in prevalence, and setting goals (action list) for the next year. In July 2025, a producer and farm/veterinary team focused discussion will be held with both a virtual and in-person option as part of the All Things BLV Conference. Producer and teams will be encouraged to attend and participate. See: https://www.canr.msu.edu/events/2025blv#:~:text=The%202025%20International%20All%20Things%20BLV%20Conference%20brings,the%20evolving%20challenges%20of%20Bovine%20Leukemia%20Virus%20%28BLV%29
One article was written by Bartlett and Kendrick to be published Hoards Dairyman. Article will be published in the near future.
Education
A lead individual from the research team is assigned to each enrolled farm and producer team. The research lead is responsible for organizing the sampling for both BLV ELISA and qPCR samples needed each year. When results are completed, Kendrick (PD) creates a consultation report, and the research lead schedules a consultation meeting. The entire research team is invited and engages with the producer team during the consultation meeting. These discussions are focused BLV education and an action list for the producer team to implement. Additionally, the research team learns of producer team concerns or interests.
Educational workshops will be held in year 2 and 3. The workshops will allow for producer teams to network and converse with each other as well as research team members.
Project Activities
Educational & Outreach Activities
Participation Summary:
Learning Outcomes
Project Outcomes
Consultation reports in 2025 will be able to respond to changes made in 2024.