Quote Originally Posted by Adam_Wysocki
URI can be identified way earlier than the point where enough mucus starts to develop in the mouth that it is easily distinguished from saliva ... at that point it has potentially progressed pretty far along and can actually be in the process of moving to the lower lung.

A vet and a culture is the absolute best way to determine whether or not your animal has a URI if you don't have any previous experience with the disease.

-adam
I agree Adam!!! Once it progresses to a visual mucus it is at high risk of entering the lower lung. Once it is present in the lungs it is very hard to get rid of and can kill an animal quickly. It is much better to catch in the earlier stages.