Author: Phil Durst, Michigan State University Extension
The 2023 International All Things BLV Conference was hosted by Michigan State University. The agenda included speakers from six countries on three continents and sought to create community around this issue that would enable future collaboration.
Producer and veterinary experiences were a critical part of this conference largely devoted to results characterizing Bovine Leukemia Virus (BLV) found by researchers. They addressed how BLV happens on the ground, what types of management decisions were made and remade to manage BLV and provided practical recommendations to producers.
The panelists were Don Niles, DVM and operations manager for Pagel’s Ponderosa Dairy and Dairy Dreams farms in Wisconsin, Brent Wilson, owner and health manager of Wilson’s Centennial Farm of Carson City, Mich., and Shaun Huser, DVM, field veterinarian with Kansas State University. Each presented lessons they have learned over years of combating the disease.
Niles has an incentive to eradicate BLV from the herds he manages since those herds are used as surrogate recipients for embryos from commercial bull studs. Export of the bulls to Europe and elsewhere requires dams of BLV-negative status. At the time of initial testing of the Dairy Dreams herd in 2017, more than 21% were ELISA-positive for BLV. ELISA is an assay that measures immune response to a specific disease, in this case, BLV.
They began to test all lactating and dry cows on the farm with an ELISA to distinguish animals that had been exposed. Initially they did not change practices to increase biosecurity within the farm. Soon they realized that testing without biosecurity is like bailing a leaky boat with a small bucket. On the same token, Niles said the corollary is that biosecurity without testing will take too long to achieve eradication. Both testing and biosecurity are essential to eradicate the disease.
Since BLV is bloodborne, their biosecurity began with changing needles after every injection. Needles can harbor microscopic blood on them after use and using the same needle in the next animal transfers that blood. Though that step put the burden on the employees who do the injections, it alone was not enough to sufficiently reduce new infections. The farm switched to a needleless compressed gas injection system which cut down on time and waste of using single use syringes as well as reducing risk of finger sticks handling needles. This has worked well, and currently remains in use.
Still not getting the reduction in new infections, they further looked at transmission routes and took steps in two other areas. First, they began changing exam sleeves after every rectal palpation. Exam sleeves can also harbor blood, though maybe not noticeable, which can be transferred to the next animal. The burden of doing this fell on Dr. Niles, but he soon developed a system that takes only a little extra time between animals. He wears a long-sleeve nylon smock that allows exam sleeves to go on and off quickly. When performing an ultrasound, the probe is encased in the sleeve which was used for the previous palpation, which is turned inside out for ultrasound of the next animal.
Lastly, even though they thought they were doing a good job with fly control on the farm, they consulted with an entomologist. Up until this point their program was to fly spray regularly, but haphazardly during fly season. It seemed to deliver some control to the fly population, but the entomologist showed them how the very tiny flies, when smashed, each had a drop of cow blood in them, likely transmitting blood between animals. Approaching fly control with an intentional program of observation and treatment ahead of population explosions has reduced flies significantly and they are using less chemicals by working ahead of the problem rather than behind.
Regarding testing, they began using the SS1 qPCR test from CentralStar Cooperative, a new test at the time that quantified the proviral load in each ELISA-positive animal. Through this, they could target the cows with the highest amounts of provirus to immediately cull, and designate others as “do not breed.”
As a result of all these measures, herd prevalence of BLV was down below 2% in 2021. Recognizing that other producers don’t have the same incentive or resources to eradicate the disease quickly from their herds, Niles thinks the “most significant interest could arise from producers and veterinarians who want to be proactive from an animal welfare or standard of veterinary care point of view. This is particularly true as the industry and profession strive to conduct business in a way that is acceptable to the evolving milk and cheese consuming public.”
Commercial Dairy Producer Perspective
Brent Wilson told conference attendees that he wants to get rid of BLV from their herd of around 1,200 dairy cows. He started paying serious attention to BLV after a herd test as part of a study with Michigan State University (MSU) showed herd prevalence to be around 37%, much higher than he had believed. They were already changing needles and continue to do so. Later, herd personnel and veterinarian began changing exam sleeves on all heifers and cows.
One of the things that testing showed him was that 18% of heifers were apparently freshening with the disease. Typically, BLV is thought to be a disease that spreads among the milking herd and that only a few animals may be infected as youngstock. This, however, showed there is a problem of disease spread before heifers have their first calf which made Wilson wonder when the heifers became infected. Wilson volunteered to be a cooperator on an MSU project where heifers were sampled at key points in their lives beginning soon after birth. Infection rates were very low at this but increased right before first breeding.
He also noted that positive heifers usually came from positive dams, even if the offspring shows up later as infected. Therefore, he has been trying not to breed positive dams, while managing the number of heifer calves he needs for an expanding herd. Through all these changes, they have been successful in reducing BLV to below 20% . They want to continue their decrease in new infections and eventually get rid of this herd disease.
“We still experience reduced fertility, more mastitis and feet and leg problems with positive cows. As our cows build productivity with each lactation, they never achieve their full genetic potential. It is simply that BLV positive cows have reduced immunity to disease,” Wilson said.
The clinical phase of BLV, which only affects a small percentage of cattle, results in tumors that will cause the animal to be condemned at slaughter. Wilson identified a problem with BLV cattle that is sometimes overlooked. Infected cattle may indeed be good milk producers, but they are prone to crash unexpectedly. And when they do, farmers have a dead animal to deal with. While Wilson and his staff try to anticipate these crashes, he said there are very few precursors.
Based on the comments by Dr. Niles during the panel discussion, Wilson said he was interested in improving their fly control because he recognizes that it is a problem despite spraying every three weeks during the season and additionally in hot weather. It seemed to him that they are always playing catch-up with the fly population.
BLV in Beef Cattle
Dr. Huser began a BLV project in conjunction with MSU to characterize BLV infection in beef cow-calf herds in northeastern Kansas. Data on beef cattle infection was outdated and seemed to indicate that BLV was mostly a dairy cattle disease problem. Recent studies in the U.S. and Canada have shown that approximately 90% of dairy herds are infected with individual cow prevalence averaging in the range of 40-50%. On the other hand, it was assumed that maybe 20-25% of beef herds would be infected, and that individual cow prevalence would also be low.
He and his students sampled almost 3,000 beef cattle from 45 individual herds in 13 Kansas counties. Herds tended to be small, with 20-40 head being the predominant size and with a mixture of larger size herds. The results left him stunned. Ninety-five percent of herds had at least one cow infected with BLV and cow prevalence was 55%. Essentially there was no difference between dairy herd infection rates and the rates he found, even though there are major management differences between dairy and beef farms. There also seems to be geographical difference in BLV prevalence in beef herds which might be accounted for through differences in insect and arthropod vectors in those regions.
They did not find any correlation between BLV-positive results and conception rates in beef cattle, nor did they see any effect of breed or pasture stocking density on prevalence. For him, it was about return on investment. At this time, we don’t know the impacts of the disease on beef cattle. As we learn more, it may be more imperative to control this disease.
Based on research, it is now understood that the majority of dairy and beef cattle producers deal with BLV-infected cattle daily. Learning from producers and their veterinarians can help reduce the risks of transmission and the impacts of the disease. Tasia Kendrick, Associate Professor at MSU and conference organizer, said “the talks presented at this conference show both the impact of this all-too-common disease and provide a general roadmap for those who want to reduce, and even eliminate it. We are committed to work together as a community of people to tackle this issue for the future of the dairy and beef industries and the producers involved.” For more on BLV, visit https://www.canr.msu.edu/blv/.
This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu.