Yeah, I'm trying to figure out what to do as well. I've been giving a MLV in the fall to bred cows for a few years with good success, but last year I had some problems. A few cows aborted right around the IBR mark, but I was unable to get them diagnosed so I'm not sure what the true cause was, it may have been pine needles. I also lost a yearling heifer 48 hours post vaccination due to allergic reaction. That was a new one since I'm used to seeing a reaction immediately post-vacc. This heifer was posted, and that was definitely the cause. The vaccine company has paid for the diagnostics, and is discussing compensation for my loss.
It's been frustrating since I vaccinate animals to protect them, not to kill them :? . I will stick with using MLV product on the calves this fall, just not sure what to give the cows.