Join Date: Aug 2009
Location: secret mountain valley
you have to specifically test for each disease so no, it would not show up on coggins. Since he doesn't seem to be running a fever, and is eating drinking urinating and defecating normally it isn't likely that there is a systemic infection. I would take his temperature and monitor his heart rate as these go up with colic, but it is very possible there are a few things going on.
He could be sad and depressed, I would be surprised if he wasn't missing his buddy actually. It could also be going through a growth spurt which takes a lot out of them. Also, when you say the vet did yearlies I assume vaccinations were part of that? These can wipe an animal out for a little bit, especially if he is growing/working hard. If the heart rate, temp and food intake and output all seem normal I would give him some time to grieve and adjust but it can't hurt to have a call in to the vet to get their opinion (since he just saw/knows your horse!) Good luck with him, hope he gets to feeling better soon.