University of Wyoming and Colorado State University veterinarians report an increase in the number of heifer abortions due to the virus responsible for infectious bovine rhinotrachetis, also known as "red nose."

Some episodes occur after vaccination with specific USDA- approved modified live viral vaccines. Multiple abortion episodes are being investigated in both states.

Donald O'Toole with the UW state vet lab, and Hana Van Campen with CSU's vet diagnostic lab report the abortion increase in a letter to the Journal of the American Medical Association.

"Often, there is a history of modified-live bovine herpesvirus-1 vaccine in some two to eight weeks prior to abortion," they write. Both veterinarians suspect live vaccine strains of bovine rhinotrachetis are responsible for some abortion outbreaks.

Producers may be using modified-live bovine herpesvirus-1 in pregnant animals without realizing they must first use a specific group of vaccines within a defined time period before the pregnant cattle can be safely vaccinated, warn the vets.

Since their letter was written in August, 2010, both labs continued to see abortions in the wake of vaccinations with specific modified live products.

Loses are ranging as high as 25%, says O'Toole.

"Typically, they occur 30-60 days after vaccination," he explains. "In almost all cases, pregnant heifers rather than pregnant cows are involved.  Aborted fetuses have characteristic histological changes in livers and other major internal organs."

O'Toole feels it is unclear what proportion of abortions is due to off-label use of these vaccines and what proportion occurs  in appropriately vaccinated animals.

"Producers who see a series of abortions one or two months after vaccination with IBR vaccines should submit fetuses and associated placental membranes to a diagnostic laboratory," he urges.

"Typically, heifers recover quickly following abortion. There is little tendency for placental membranes to be retained."