News October - November 2020
Consequences of ignoring BLV By: Kelly Sporer, PhD, Diagnostic Technical Specialist, CentralStar
Every day you make choices about priorities for your dairy. Bovine Leukosis, caused by Bovine Leukemia Virus (BLV), may not have made your priority list yet, but it should. New research continues to confirm its impact on production and profitability. Here is a glimpse of what happens when you ignore BLV.
Herd immunity is compromised BLV influences the way a cow’s immune system works and in turn, likely affects her ability to fight off other infections. BLV-positive cows respond differently than their negative herdmates when vaccinated, implying that infected cows are not as protected against diseases for which they are immunized.
BLV's effect on Rolling Herd Average
Rolling Herd Average (RHA)
Milk production drops Results of multiple studies show that BLV-positive cows with higher ELISA test values have lower predicted 305-day mature milk yields, in addition to a lower 12-month RHA. Results from three research studies1 show that each 10 percent increase in BLV prevalence is associated with a 428.9 pound loss in RHA per animal in the herd.
Percent BLV-positive animals in the herd
Cows don't live as long BLV-positive cows are 23 percent more likely to leave the herd more quickly over the next two years compared to their negative herdmates. Research in over 100 Michigan herds shows a direct correlation between a higher BLV prevalence and the number of third and greater lactation cows that stay in a herd. BLV-positive cows with a higher ELISA value are less likely to stay in the herd, negatively impacting whole herd longevity.
More than 20 years ago USDA reported that 89 percent of all U.S. dairies were infected with bovine leukosis. A 20182 study discovered it's only getting worse with 94.2 percent of herds identified as having at least one BLV-positive cow.
BLV's effect on Life Expectancy
Negative
Survival Probability
It spreads BLV is easily transmitted between animals by using the same needle or breeding sleeve on multiple animals. Increasing the risk even more are the animals that shed the most virus, called “Super-Shedders”. These animals are the most contagious and pose the greatest danger to infecting herdmates.
Three research studies show that each 10 percent increase in BLV prevalence was associated with a 428.9 lb. loss in RHA for each animal in the herd.
BLV-positive cows leave the herd approximately three months earlier compared to negative herdmates.
Positive
Days 1996 National Animal Health Monitoring Study (NAHMS), Michigan State University & CentralStar Coopera-
1
tive, 2016 NAHMS. 22018 LaDronka, Veterinary Medicine International