During the NCBA trade show last week, convention participants had an opportunity to sit in on short educational sessions on a variety of topics at the Learning Center on the trade show floor. During one well-attended session, Jerry Woodruff, DVM, with Boehringer Ingelheim Vetmedica Inc., discussed research on vaccinating young calves for pathogens associated with bovine respiratory disease and on vaccinating to prevent losses associated with bovine viral diarrhea (BVD).
Woodruff notes that BRD in pre-weaned calves, sometimes called “summer pneumonia,” can be a costly problem. Twenty years of data from the U.S. Meat Animal Research Center showed an incidence ranging from 3 to 23 percent, with an average incidence of 10.5 percent. The average age of infection in pre-weaned calves is around 100 days, corresponding with the time when calves experience a gap between maternal immunity from colostrum and full development of active immunity. Some calves are affected earlier, such as within the first month after birth – usually indicating they did not receive adequate quantity or quality of colostrum at birth,
Research has shown that calves affected by BRD prior to weaning sacrifice about 17 pounds of weaning weight compared with healthy calves. Those infected during the first 28 days after birth give up 35 pounds of weaning weight.
Vaccinating calves early, while still protected by maternal antibodies, can improve their immune response later, Woodruff says. He outlined a research trial in which young calves were vaccinated using a modified-live viral vaccine, then challenged with a virulent BVD type 2 virus seven months later. Vaccinated calves had a significantly lower incidence of morbidity than control calves in this trial, indicating they were able to mount an immune response to the vaccine while still protected by maternal antibodies.
Shifting to BVD, Woodruff outlined how cows exposed to the virus during gestation are at high risk for early embryonic death or abortion later in their pregnancy. Those infected between about 45 and 125 days of gestation can produce a persistently infected (PI) calf, which will shed the virus throughout its lifetime.
Scientists have isolated three types of the BVD virus – type 1a, type 1b and type 2a. In recent years, BVD type 1b has become the most prevalent, accounting for about 46 percent of cases compared with 28 percent for 1a and 26 percent for 2a. Fortunately, Woodruff says, vaccinating cows with vaccines derived from type 1a and type 2a BVD virus appears to provide protection against the type 1b virus.
Research has shown, Woodruff says, that vaccinating calves for BVD and IBR using a modified-live viral (MLV) vaccine 30 to 60 days prior to breeding can significantly reduce abortions due to those reproductive viruses and virtually eliminate the occurrence of PI calves. He adds that MLV vaccines can be administered safely to cows during gestation, but only if the cows received an earlier dose of the MLV vaccine at least 30 days prior to breeding.