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Vet discusses blood-borne bovine leukosis virus

by Wyoming Livestock Roundup

Kansas State University’s Director of Production Animal Field and Investigations Gregg Hanzlicek shares his knowledge on the bovine leukosis virus (BLV) and discusses its origins, symptoms and strategies for management. BLV is not a new virus, he says, but one producers have discussed for years. 

“The origins of the virus are unknown, but veterinarians understand how it’s spread.” Hanzlicek says. “We know BLV is basically everywhere.” 

Hanzlicek explains once livestock become infected, they will be infected for the duration of their life, and it can affect bovine of any age. 

“BLV lives in white blood cells – this is where the ‘leukemia’ or the ‘leukosis’ part of the disease comes from,” shares Hanzlicek. “To spread this organism from animal to animal, movement of blood is requried from a positive cow or calf to a negative animal.”

Clinical signs
and symptoms

Hanzlicek discusses several clinical signs and symptoms, noting BLV is a tumor-causing virus.

“Some symptoms producers might see are black stools because the tumors produce ulcers,” he explains. “Sometimes the tumor will localize in the spinal cord, so this disease could present in downed cows.” 

A small percent of infected livestock will show clinical signs. According to Hanzlicek, less than five percent of all cows that test positive show clinical signs.

Hanzlicek notes a research study looked at over eight million cows in the U.S noted BLV is the second most common reason why cowherds are condemned at slaughter.  

“The cattle look normal and pass  pre-slaughter inspection, but are condemned because of tumors presented at slaughter,” adds Hanzlicek.

He mentions the problem with BLV is in most operations, high percentages of cattle test positive, though only a few present symptoms. 

and strategies

Hanzlicek shares three management strategies for producers with positive testing cattle. 

The first strategy – managing the spread of BLV – includes preventing transmission of blood from one animal to another.  

“Surprisingly, there is research that shows rectal palpitation when pregnancy checking an infected animal can pass it along to the next animal,” Hanzlicek shares. 

He explains not cleaning or changing needles between animals is the number one reason for transmission. In addition, not cleaning a tattoo gun, pliers, palpation sleeves and ultrasound probes can be also a cause. 

“Unfortunately, on the bovine side, veterinarians have zero treatments for all viral diseases,” notes Hanzlicek, sharing there are no vaccines or treatments. 

The second strategy for management includes separating animals that test positive.

“Let’s segregate or find out who’s positive in the herd and put them in one group,” Hanzlicek says.  “Animals that test negative may be kept in another group so producers don’t have to worry as  much about the negative group contracting BLV.” 

Hanzlicek shares summer and horse flies can also transfer the virus. 

“During pasture seasons, these two groups need to be separated as far as possibly to prevent the spread from flies,” says Hanzlicek, noting during the winter months producers don’t need to be concerned about flies, but should keep all equipment sanitary.

The third strategy for BLV mitigation  is for producers to consider culling positive livestock. 

Positive animals are the source for negative animals, Hanzlicek shares. 

“Say we have 100 cows, we test all 100 and two cows test positive for BLV,” he says.  “Economically, it might make sense to send positive testing animals to slaughter.” 

In the instance a rancher has 30 or 40 head from a herd of 100 test positive, it would not make sense to send  the infected cattle to slaughter, he notes. 

There have been several advancements in diagnostic testing for BLV, Hanzlicek shares. 

“The test includes a simple blood sample from each animal and a polymerase chain reaction (PCR) test,” he explains. 

The PCR looks to see how much of the virus is in the test animal’s bloodstream. The producer and veterinarian can then discuss the risk of the top 10 percent of cattle and consider culling highly infected livestock, Hanzlicek notes. 

“Any herd operation wanting to remain free from this disease has to practice management strategies to prevent the spread of BLV,” says Hanzlicek, sharing they are necessary in order to control the spread. 

Hanzlicek concludes by sharing producers need to be vigilant in managing signs and symptoms, especially during calving season. 

“We’re probably not going to get rid of BLV  and it’s going to be difficult, but there are ways to manage this disease and keep the negative effects of it as minimal as possible,” he says.  

Information in this article was presented in an Oct. 26 episode of the Beef Cattle Institute’s CattleChat podcast. 

Brittany Gunn is the editor of the Wyoming Livestock Roundup. Send comments on this article to

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