Modified live virus vaccines covey a longer lasting immunity but can cause pregnant animals to abort. Killed virus vaccines should be given twice, at least two weeks apart the first time to build sufficient immunity. Giving a booster shot each year is recommended to build higher levels of antibodies that will be passed on to the developing fetus. In other words, you re-vaccinate the cow to protect the calf. Usually purchased in combination with BVD vaccine.
Severe diarrhea is rare but of more concern is the suppression of the immune system.
The same precautions as listed above for IBR apply to BVD vaccines and immunity. PI3 - Parainfluenza Type 3 also causes respiratory problems which can be complicated if IBR and BVD infections occur at the same time. BRSV - Bovine Respiratory Syncytial Virus is not so important for the disease it causes but for the diseases it allows to take place. Infected animals are not able to fight off other respiratory infections, respond poorly to treatment and often drown in their own lung fluids. Lepto - Leptospirosis is a widespread problem in the south, especially in unvaccinated herds.