Chronic Catarrh (or Nasal Gleet, or Collection in The Sinuses).

This is a subacute or chronic inflammation of some part of the membrane affected in common cold, the disease just described. It is manifested by a persistent discharge of a thick white or yellowish-white matter from one or both nostrils. The commonest cause is a neglected or badly treated cold, and it usually follows those cases where the horse has suffered exposure, been overworked, or has not received proper feed, and, as a consequence, has become debilitated. It may occur as a sequel to influenza.

Fonte: Diseases of the Horse