How is your foal? This sounds like the classic choke from eating mom's poop. If it hasn't resolved you need to get a vet out ASAP as it will be life threatening. If it has resolved on it's own pay attention to his breathing for a while...if he sounds gurggly (sp?) or coughs then he may have inhaled some of that and can develop pneumonia. Again you will need a vet.
Sometimes you can massage the throat, gently, downward and relieve a choke, but usually if stuff is coming out the nostrils it is beyond what a layman can do and a vet is needed.
Good luck with your baby.
Charlotte