I used to give the IN version to a herd of about 90 horses yearly, and while some would get head-tossy knowing what was coming, with the proper timing and care about not stepping in their way, we had no violent issues. But every horse is different. It’s definitely surprising, and they certainly don’t like it, but we never had anybody striking out, trying to leap away or rear.
I believe my vet told me once that it’s a myth that if horses have strangles once, they’ll have immunity to it later. They said the immunity will last several years, but not last a lifetime. I’m not a vet, so I don’t know if that’s fact, but it definitely made me think twice about vaccinating my older horses (when they were in an exposed situation, now they’re pretty much a closed herd and I don’t worry about it.)
