CALF_News_October_November_2021

28 CALF News • October | November 2021 • www.calfnews.net By Burt Rutherford Contributing Editor W ant to start a discussion with the world affairs experts at the corner table in the sale barn cafe? Ask their thoughts about when you should vaccinate your cows before breeding and whether or not you should use a modified-live virus (MLV) shot. Opinions will abound. But casting eyeballs at some recent research might shed light on the subject and give you the advantage of facts when you next stir the coffee club a little. It is widely recognized by researchers and veterinarians that MLV vaccines are better because they create a more robust immune response in the animal. But MLVs come with some considerations. If not handled correctly by keeping them cool and using everything in the bottle in a timely manner, MLVs can lose their effectiveness. And MLVs have always gotten a rap for causing abortions if given to naive, unvaccinated heifers or cows. Is the rap warranted? According to research that George Perry, Ph.D., and others did at South Dakota State University (SDSU), it may well be a consideration for cow-calf producers. That’s not to say that MLVs shouldn’t be used on cows pre- breeding, but there may be some management considerations to keep in mind. Perry, formerly at SDSU, now is an associate professor and reproductive physiologist at the Texas AgriLife Extension and Research Station in Overton, Texas. In an earlier study, Perry and others vaccinated a group of naive heifers. “And what we found in that study was that the modified-live vaccines disrupted reproductive performance, not only with the dominant follicle, but we had poor conception rates after the synchronization protocol [using timed artifi- cial insemination (AI) with controlled internal drug release (CIDRs)].” What’s more, a few of the heifers short cycled again on the next breeding. “We know that, for at least two cycles, we were having problems. And so, especially in naive animals, by stay- ing away from modified lives at the start of a breeding season or close to the start of the breeding season, even when we’re using synchronization protocols, that we get better control of follicular growth; fertility was increased,” he says. Then the question became what happens in a cow herd or in animals that have been well vaccinated? And by well vac- cinated, Perry says animals that were vaccinated as calves and then given an annual booster every year. So Perry and crew compared an inactivated or killed vaccine with an MLV and a control group that got a saline solution. “And what we saw is, even in animals that had previously been vaccinated, if we gave a modified live 30 days prior to the start of the breeding season, we had a negative impact on AI conception rates.” The researchers followed that with a similar on-ranch study and saw similar results. Between the two studies, they evalu- ated results on more than 3,000 head from nearly 20 herds. “And so across both of those studies we’ve done, we have seen differences in AI conception rates if they’re given a modi- fied live pre-breeding,” Perry says. However, in the second study, instead of giving the shots exactly 30 days pre-breeding like they did in the first study, they ranged from 27 to 89 days pre-breeding. “And we saw the negative effects across that whole time period. And so we know something is going on there.” However, the effects were decreased once the cattle got out past 45 days. “And so if somebody asked me, ‘Well, I really want to use a modified live right now,’ I look at the data and say, OK, but we probably need to get it into them at least 45 days pre-breeding and get those two extra cycles out of the way,” he says. Consider a One-Two Punch Given that conclusion, Dr. Lee Jones looked at additional research and related a one-two vaccination strategy at a Cattle- men’s College session during the 2021 Cattle Industry Con- vention in Nashville, Tenn. Jones is an assistant professor and clinical veterinarian with the University of Georgia’s Investiga- tive and Diagnostic Laboratory in Tifton, Ga., and a cow-calf producer. Looking at research from Auburn University, Jones showed data on heifers given an MLV at five to seven months of age, another MLV six months after that and then bred with timed AI and bulls. At pregnancy check, the heifers were vaccinated again with either an MLV or killed vaccine. MLV or Killed Which Is Better at Pre-Breeding?