Horse Veterinary Questions? Ask an Equine Vet.
Hello. Thanks for the question.
I'm sorry for the long wait, I just logged in and saw this.
He should be able to breathe ok, but he may have to open his mouth at times. The difficult thing here is finding the quill that is likely buried as they migrate quickly under the skin. He will likely end up being anesthetized and then any areas of swelling are surgically opened and explored to find the quills. It's always easiest to find them right after it happens, but often times we need to go back and find more well after the fact.
In the end, this should be resolved fully. The swelling can be treated with an anti-inflammatory medication like Rimadyl.
I hope this helps, let me know if you have any other questions.