MLV Intranasal (IBR/PI3/BRSV) vaccines are safe for pregnant cattle; injectible MLV vaccines containing IBR are NOT, unless the cows in question have been through a prescribed regimen of two doses prior to breeding - every case of IBR abortion I've seen in the last 25 years was vaccine-induced... MLV vaccines used in cows without appropriate previous vaccination.
The intranasal vaccines do a GREAT job priming the immune system, and boostering with an injectible MLV product afterward is good - but if you're dealing with pregnant animals not previously vaccinated, two doses of intranasal at 3-4 wk intervals, or intranasal followed by a 'killed' viral injectible can do a pretty good job of protecting against IBR/PI#/BRSV, without risking vaccine induced abortion.
Clostridial bacterin/toxoids are safe for all ages & classes of cattle, including pregnant cows. Most folks don't vaccinate/re-vaccinate adult cows, but if vaccination history is sketchy or nonexistent, it's not a bad idea to vaccinate... it's cheap insurance, if you will. I have seen adult cows, with a good history of calfhood vaccination, die of blackleg - usually cows in an estrus-synchronization program, receiving IM doses of prostaglandin products. So... it may not be a bad idea to 'booster' adult cows in your herd with a Clostridial bacterin/toxoid(containing tetanus toxoid) every few years... I don't advocate every year, but we tried to booster our adult cows every 3 years or so - if nothing else, it may have helped provide additional colostral antibody protection to calves.
Wife(also a DVM) and I have been working with a young couple who recently purchased a nearby farm and herd of cattle. Knowing the previous owner, and the fact that there were no pens or working facilities on the place until these kids bought it... I doubt that any of these cows had ever had a vaccination of any sort. So... we recommended vaccinating the entire herd with an 8-way Clostridial bacterin/toxoid and Triangle 10HB... just finished helping them give the booster doses yesterday.