Be on the Lookout for Bovine Leukemia

September 30, 2015 11:19 AM

Veterinarians and some farmers have known for decades that bovine leukemia virus (BLV) is a silent, insidious disease that impacts milk production, longevity and immunity.

Recent research out of Michigan, however, shows it can be a huge financial drain on both your bulk tank and your checkbook, says Ron Erskine, a Michigan State University (MSU) veterinarian and lead
researcher on the project. The Michigan State study, done in 2010 with 113 herds, shows milk losses of 220 lb. per cow for every 10% of cows in the herd infected with BLV.

If you assume a third of your cows are infected, that means a milk loss of 725 lb. of milk per cow. Multiply that times your mailbox milk price. Even at $16 per cwt, that’s a loss of about $120 per cow, or $12,000 for every 100 cows in your herd. Ouch.

And don’t assume your herd is not infected. In the MSU study, 98 of the 113 herds studied (87%) were
infected. This mirrors a National Animal Health Monitoring System study in 1996, which found 89% of U.S. herds were infected with BLV.

Of the Michigan infected herds, 33% of the cows were infected. In these herds, 40% of cows in their third lactation were infected; 45% were infected in their fourth and later lactation.

About 5% of cows with BLV will develop tumors. When federal meat inspectors find these tumors, they will condemn the carcasses. Note: About 20% of all condemned cows have lymphoma tumors.

Because it is a virus, BLV does not respond to antibiotic treatment. There is no cure. So the only defense is prevention. If there is any good news, it’s that BLV takes several lactations to establish itself.  
BLV is carried in blood, milk and colostrum. So the first line of defense is sanitation. Shared needles are a transmission risk factor, as are gouge dehorners, tattoo pliers, tail dockers and palpation sleeves.

Though it is not believed to be transmitted via semen, natural breeding is also a likely transmitter as a result of blood exchange due to trauma during breeding, Erskine says. “In a related study of beef breeding bulls, the infection rate increased from near zero in virgin bulls to 66% in bulls that were greater than five years old,” he says.

The key to reduce infections is to prevent calves from getting it in the first place. Pasteurization or freezing of colostrum destroys the virus and prevents transmission, Erksine says. On the other hand, feeding unpasteurized, pooled colostrum from multiple dams can infect many calves at once. In addition, biting flies could be carriers, so an effective fly control program is essential. Also, test animals before purchase.

There is no short-term fix, but these preventative steps are worth the effort. If you reduce the prevalence of BLV in your herd, you’ll see higher milk production, greater longevity and fewer disease problems, Erskine says.

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