Throats can tell us a lot, but can mislead us as well. When looking at the throats, most importantly is the amount of inflammation or redness. The inflamed throat can be caused by several things including trichomoniasis, respiratory infection, and irritation from poor ventilation. Birds will not, and can not perform to their capacity with inflamed throats. As trichomonas numbers go up, performance goes down.
Respiratory infections can be more difficult to diagnose and deal with.
One good thing is that the old birds do not become infected nearly as easily or as often as do young birds. It is most frequently associated with overcrowding, poor ventilation, and dampness, especially dampness when cool. The amount and quality of mucus in the throat is more difficult to interpret. The birds, like us have different qualities of saliva-some thicker, some thinner. Just the presence of mucus threads when opening a birds mouth is not necessarily bad.