Growing evidence suggests modified live virus (MLV) IBR vaccines are doing more harm than good when given to pregnant cattle.
Infectious bovine rhinotracheitis (IBR) is a herpes virus. Like all herpes viruses, IBR can go into a latency phase within the animal’s brain. But when the animal is stressed with another shot of the live virus, the virus is reactivated, enters the blood stream and migrates to the ovaries and fast growing tissue like embryos and fetuses.
Once there, it replicates and does its dirty work, says Chris Chase, a veterinarian with South Dakota State University. “Reproduction is a big problem with this virus,” he says.
“Diagnosticians now have enough experience with these episodes to say that post-vaccination abortion can occur following on-label use of vaccines with modified live vaccine IBR virus,” adds Donald O’Toole, a veterinarian with the University of Wyoming. “It is not just a problem when MLV vaccines are used off-label, as has been known for years.”
Abortion storms and poor reproduction can result, says Doug Scholz, director of veterinary services for Novartis Animal Health. He points to a number of large, western dairies that were experiencing high numbers of abortions and poor conception rates when MLV IBR vaccines were given in the dry period and close-up pens.
One dairy Colorado dairy was seeing nearly a 25% abortion rate and conception rates of just 30%. When the dairy stopped using the MLV IBR vaccine, abortions dropped to 8% and conception rates climbed to 45%. On a second dairy, pregnancy losses dropped from nearly 30% to less than 10% and conception rates jumped by 15% when the ML IBR vaccine was no longer used.
At the University of Wyoming (UW), researchers were finding one or two aborted fetuses per day 30 to 40 days following a MLV-IBR vaccine given when Angus heifers were seven months pregnant. Total losses were 25% in the 55 heifers studied. “There was no other evidence of infection other than IBR,” says O’Toole. “My recommendation: Use inactivated IBR vaccines on breeding females.”
The tendency for the IBR virus to go into latency is also a problem when young calves are vaccinated with a modified-live vaccine. When they’re later stressed, the virus can be reactivated. While this may only cause a slight fever for a day or two in the vaccinated animal, that animal can also shed live, virulent virus to pen mates. If these animals are not vaccinated, an IBR outbreak can occur, says Clinton Jones, a veterinarian with the University of Nebraska.
His bottom line: “Do not use a ML-IBR vaccine on young animals and do not mix unvaccinated calves.”
Inactivated IBR vaccines for both cows and calves are the preferred method of vaccination, say these veterinarians. “Inactivated vaccines will decrease symptoms during clinical outbreaks, and they eliminate the possibility of virus spread to the fetus,” says Jones.
For more information, contact your veterinarian, or go to www.virashield.com or www.youtube.com/cattletalk .