What is in this article?:
The prevalence of cattle persistently infected with Bovine Viral Diarrhea (BVD) virus continues unabated in the feedlot and stocker pasture.
“Disease prevention is more important today than it’s ever been because of the high capital requirements,” says Bill Hessman, DVM, Haskell County Animal Clinic at Sublette, KS.
Yet, when it comes to preventing Bovine Viral Diarrhea Virus (BVDV) and exposure to cattle persistently infected (PI) with the virus that can overwhelm immunity, there's been little progress made in a decade.
Hessman established Central States Testing (CST) in 2005. It was the first commercial laboratory to offer PI-BVDV testing. CST tests about 540,000 head annually – 90% of which are high-risk feedlot and stocker cattle. The prevalence rate based on that testing remains extraordinarily stagnant at 0.38-0.42% each year. Incidentally, Hessman estimates approximately 2 million head are tested industry-wide each year.
“The overall prevalence rate in the class of cattle I deal with has stayed the same, but I expect it to increase,” Hessman says (more later).
Total cost of BVDV was estimated at $1.9 billion annually in 2011. That was based on a cost of $35-$56/calf estimated by Julia Ridpath, a USDA Agricultural Research Service research microbiologist.
BVDV Increases BRD Risk
Though the prevalence rate of PI-BVDV is miniscule in feedlots, the impact of exposure to other animals is gargantuan.
Guy Loneragan, then at West Texas A&M University and now a Texas Tech University professor of epidemiology and animal health, led a study beginning in 2002 that estimated the prevalence of PI in 2,000 head of sale-barn calves arriving at a commercial feedlot.
“Relatively few PI cattle arrive at feedlots. However, those cattle are more likely to require treatment for respiratory tract disease and either become chronically ill or die than cattle that are not PI,” the study concluded. “In addition, they are associated with an increase in the incidence of respiratory tract disease of in-contact cattle.”
“BVD affects Bovine Respiratory Disease (BRD) and it does so through immunosuppression,” Hessman says. “BVDV appears to be a catalyst for the common pathogens we deal with because of the immunosuppressive effect of the virus.”
In Loneragan’s study, prevalence of PI on arrival was estimated at 0.3%. Cattle exposed to PI animals were 43% more likely to be treated for respiratory tract disease.
Loneragan emphasizes the study he led was observational in nature. “Just because we saw an association between exposure to PI animals and increased respiratory disease in cattle that could have been exposed to them doesn’t mean there is a causal relationship,” he says.
One outcome that Loneragan says did surprise him was that BVDV was 10 times more likely to be present in the study’s chronically ill and deads. Other studies have found similar implications. Still others, including a seminal one conducted by Hessman, found less statistical correlation.