The latest on Bovine Virus Diarrhea - Type I and II
Bob Mortimer, Clinical Veterinarian, CSU
Increased incidence of abortion, unexplained calf deaths or congenital defects may be signs of bovine virus diarrhea (BVD). Often thought of as a disease more prevalent in feedlot operations, BVD has roots on the ranch.
BVD (bovine virus diarrhea), which has been around since the 1940s, is still a problem today, Bob Mortimer, DVM, told attendees of the Range Beef Cow Symposium. He encouraged producers to have a monitoring/surveillance plan, test all new herd additions and in high-risk herds have an eradication plan for persistently infected animals.
According to clinical veterinarian Bob Mortimer, of Colorado State University (CSU), animals infected with BVD may display diarrhea and slobbering fever, but not all infected animals exhibit obvious symptoms. BVD is immune suppressive, making the animal more susceptible to infection from other diseases. Animals may also be persistently infected (PI) and appear normal while spreading the virus to many other animals.
Mortimer told attendees of the 2003 Range Beef Cow Symposium that less than 4% of U.S. herds are thought to have any PI calves, but 20% of herds with a history of BVD are likely to include PI animals. Along with shedding the virus and exposing herdmates to infection, a PI female that survives to maturity and enters a breeding herd may produce PI calves. PI bulls may also shed the virus through semen, infecting females and calves they sire.
Herd effects due to BVD are varied and depend on the level of exposure. Mortimer cited evidence that BVD can lower pregnancy rates by 6% percent. Incidence of abortion may increase by 4%-8%, and live calf losses may increase by 3%-6%.
"When you add up the losses, its quite substantial. The overall calf crop can be reduced by 10% to 20%," Mortimer said, noting a potential economic effect of $15 to $24 decreased return per cow annually.
Mortimer advised producers to consider BVD control strategies. All cow-calf producers should have a monitoring plan to prevent introduction to the herd. Herds with a history of BVD should test for the disease and remove all PI animals. Mortimer advised a biosecurity plan involving testing of purchased animals that will be added to the herd.
He warned that vaccination is not effective against persistent infection. Vaccination programs should target fetal protection. Mortimer says modified-live-virus (MLV) vaccines have shown greater efficacy than inactivated or "killed" vaccines.
by Troy Smith
Read these other Angus Journal articles about BVD
Attack BVD Head-On
BVD in the feedlot: Control Starts at the Ranch"
Vet Call: Persistent infection with BVD
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