LOL, sounds like a Kodak moment
. I wouldn't worry about it. It is unlikely that a lone coyote would even attempt to take down a full sized horse and if he did, would likely get kicked for trying. If there were a whole pack, then I might be more worried but even then, a horse is awfully big prey for animals so small as coyotes (unless yours are a ton bigger than what we have down here). I think my biggest worry would be rabies. Around here, coyotes are carriers and all it would take was one little nip to infect your horse. However, so long as you are keeping up with his shots, I'm sure it's fine.