Which airline? And is the flight operated by the same airline that is holding it? I ask because I had an Alaska Air flight which was received by American Airlines. Most airlines will require him to be, at least, given a health certificate (declaring them healthy enough for the flight) within ten days of flight

Also, be prepared to be stared at and swarmed as if you are a flipping one eyed purple people eater. I had so many people bum rush me because they wanted to pet the puppy(ies) I was carrying with me.