OhLaLa, if the lamb is doing everything normally, the chances are that I for one would not notice a bit of an occasional snuffle when it's sleeping. BUT... since you have, and have raised it... I for one am not comfortable to say unequivocally "don't worry, it'll be fine" - so, if you are worried, you could give it a shot of antibiotic, just in case there is some low-level bacterial infection there. But from how you describe it, I think it would get nothing if it were here and in all likelihood would grow up just fine

Not sure that helps much, but at least it's a response!
