Final answer:
The Infectious bovine rhinotracheitis (IBR) vaccine can result in abortion when administered to a naive pregnant heifer.
Step-by-step explanation:
The vaccine that can result in abortion when administered to a naive pregnant heifer is the Infectious bovine rhinotracheitis (IBR) vaccine. This vaccine is known to cause reproductive issues in pregnant cows, including abortions, fetal death, and infertility.