Bovine Leukemia Virus (BLV) could be lurking in your herd right now—and you wouldn’t even know it. This silent disease is already costing the cattle industry millions, especially in dairy herds. While it often flies under the radar, BLV can have a profound financial impact, leading to lost production, higher vet bills, and the need to replace affected animals. Even if your cattle look healthy, the virus could still spread, putting your operation at risk.
The financial impact of BLV extends beyond individual herds, casting a shadow over the entire cattle industry. A major slaughter plant in the Northeast, for instance, processes around 350,000 cattle a year, and about 2,000 carcasses are condemned due to this disease alone. While the dairy industry currently bears the brunt of these losses, beef herds are not immune. Indirect costs like restrictions on selling infected animals can silently erode your bottom line. When the virus is left unchecked, it becomes a long-term problem that’s challenging to manage.
Once BLV infiltrates your herd, eradicating it is no easy task. However, the key to controlling the disease lies in preventing its spread from cow to cow. Since it’s mainly transmitted through blood and bodily fluids, implementing good management practices—like cleaning equipment and using fresh needles—can make a significant difference. A robust herd health plan is your best defense against BLV, preventing it from becoming an important issue and saving you time, money, and stress in the long run.
What is Bovine Leukemia Virus (BLV)?
The bovine leukemia virus is a retrovirus capable of causing cancer in cattle. It is a blood-borne disease that survives in white blood cells. Other names for this virus are Enzootic Bovine Leukosis, malignant lymphoma, or lymphosarcoma. The thing about it is that only about 5% of the cows that are infected will ever develop clinical disease. If that happens, then the primary sign will be the development of tumors.
This virus is transmitted primarily by the transfer of blood or other body fluids from infected animals to non-infected animals. Blood-contaminated needles, dirty syringes, OB sleeves, dehorners, tattoo pliers, hoof knives, and others are potential carriers. As you may have guessed, how you manage cattle will play a part in its transmission. Close contact with infected nasal and ocular secretions can also play a part.
Why is BLV on the Rise?
Bovine Leukemia Virus (BLV) has been around for decades, first discovered in the 1970s, but it’s becoming a bigger problem than ever. Cases have been steadily rising, and recent research shows just how widespread the virus has become. A study in eastern Kansas found that 42 out of 44 herds had at least one infected cow—meaning BLV is likely more common than many producers realize. Even more concerning is that over half of the individual cattle tested in that study returned positive.
To put that into perspective, back in 1997, the National Animal Health Monitoring System found that only 38.7% of herds had BLV, with just 11.5% of the cattle tested showing infection. That means infection rates have more than doubled in the last couple of decades, raising serious concerns about how fast this disease is spreading. While it’s often considered a more significant issue in dairy cattle, beef herds aren’t clear. The steady increase in cases suggests that if producers don’t take steps to control it, BLV will continue to spread, leading to more losses down the road.
So why is this virus making such a strong comeback? One reason is that it often goes unnoticed since only a small percentage of infected cows actually develop visible symptoms. This lack of notice allows the disease to silently circulate within herds for years before anyone realizes there’s a problem. Modern cattle management practices, like shared needles, dehorning tools, and even colostrum feeding, can unknowingly contribute to transmission. However, with regular testing and strong prevention measures, you can take proactive steps to stop BLV from spreading, making it easier and less expensive to manage over time.
Three Possible Outcomes of BLV Infection
Regarding the Bovine Leukemia Virus (BLV), not all infected cattle will show the same effects. In fact, the most common outcome is that an infected cow won’t show any symptoms at all. These asymptomatic carriers can live a normal life while unknowingly spreading the virus to other cattle in the herd. This is one of the biggest challenges with BLV—because there are no obvious signs in most cases, it can spread silently for years before a producer even realizes there’s a problem.
The following possible outcome affects about 30% of infected cattle: They develop a condition called persistent lymphocytosis. This means they have a consistently high white blood cell count, which can weaken their immune system over time. While these cows may not appear sick, they could be more vulnerable to other diseases and may not perform as well in terms of milk production or weight gain. Even though they don’t develop full-blown cancer, their overall productivity could still take a hit, leading to hidden economic losses for producers.
The most severe outcome is also the rarest—less than 5% of infected cattle will develop cancerous tumors. When this happens, the cow may show signs like weight loss, enlarged lymph nodes, or difficulty breathing, depending on where the tumors form. Unfortunately, there’s no cure once BLV progresses to this stage, and these animals will either die or need to be culled. While cancer cases are rare, they serve as a reminder that BLV isn’t just a harmless infection—it has the potential to cause serious problems for both individual cattle and entire herds if left unchecked.
Signs to Watch For
Cattle infected with Bovine Leukemia Virus (BLV) can sometimes show subtle symptoms that may be easy to overlook at first. One of the earliest signs is a general loss of appetite, which can lead to noticeable weight loss over time. Digestive issues may also develop, making it harder for the animal to absorb nutrients and maintain body condition properly. In some cases, infected cattle might experience recurring fevers, weakening their overall health and making them more vulnerable to other diseases. Eye problems, such as cloudiness or inflammation, can also be a sign that something is wrong.
More severe symptoms can appear as the disease progresses, especially in older cattle. Some cows may develop hind limb paralysis, which affects their ability to walk and move around, making them easy targets for injury or further complications. One of the biggest red flags for BLV is the presence of enlarged lymph nodes, which can sometimes be felt under the skin or seen as noticeable swelling. In rare cases, tumors may form in various parts of the body, including major organs, leading to significant health issues. These more advanced signs typically show up in cattle three years or older, making early detection and management crucial to keeping the herd healthy.
No Cure, So Prevention is Key
Currently, there is no cure for Bovine Leukemia Virus (BLV), which means that once a cow is infected, it stays infected for life. This makes prevention your best line of defense. Keeping the virus out of your herd starts with testing and biosecurity measures to limit exposure. Since BLV spreads through blood and other bodily fluids, using clean needles, properly disinfecting equipment, and preventing contact between infected and healthy cattle are all crucial steps. Without these precautions, the virus can silently spread through your herd before you even realize there’s a problem.
Ways to Prevent the Spread of BLV
- Test your herd – Identify infected cattle early to manage the spread.
- Use clean needles and equipment – Never reuse needles, and disinfect dehorning and tagging tools between animals.
- Limit contact between animals – Reduce nose-to-nose contact and prevent cross-contamination through blood or bodily fluids.
- Control insects – Biting flies can spread the virus, so fly control is essential.
- Be cautious with colostrum and milk – BLV can spread from infected cows to calves through milk and colostrum.
If BLV does show up in your operation, your main options are managing the spread or culling infected animals. While culling can be a tough decision, removing infected cattle can help protect the rest of the herd and prevent long-term losses. Some producers choose to keep infected cows and manage the risk, but this requires strict biosecurity and ongoing monitoring. Knowing which animals carry the virus lets you make informed decisions that balance herd health with profitability.
Stopping the Spread of BLV
You should separate the negative and positive animals into separate groups. This will help prevent any contact between the two and stop any potential spreading. If you need to work for the two groups, you should do the negative ones first, so you won’t accidentally carry the disease on any equipment.
You should always clean and sterilize any equipment you use, such as tattoo equipment, ear taggers, nose tongs, hoof knives, and castrating equipment. Use disposable needles and discard them after every use to prevent cross-contamination. This is an excellent strategy to follow, even if you are not trying to stop this disease from spreading.
Since the virus is spread through bodily fluids, it may be necessary to provide a colostrum replacer in case any of your cows become infected. As with the others, separate any potentially infected calves away from the others until test results show that they are not infected.
Although it is not necessary, testing your herd every six months can help prevent the spread. The testing will track the producer’s control progress, and you can check if horizontal transmission is occurring and which animals are infected. The Texas A&M Veterinary Medical Diagnostic Laboratory offers testing for this virus at $27 each.
Testing and Long-Term Prevention.
The main way to prevent this virus from showing up is to test every new animal that enters your operation. If possible, separate them from your herd until you can determine their status. Be sure to manage all new arrivals as positive until the test results come back with a different story.
As with any other disease, do not buy animals from anyone you do not know. This may be a fairly dumb thing to say, but there are some people who would do that just because it seems like a good deal. If you do not know the source, you could bring anything to your place. Just remember: if it sounds too good to be true, then it probably is.
A few states have developed voluntary programs for the control of the Bovine Leukemia Virus (BLV). These programs can certify BLV-free herds by removing infections and certifying that the herd is BLV-free. For the herd to be certified BLV-free, it must pass three consecutive negative tests 60 to 90 days apart.
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