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Ask The Vet: Upper Airway Concerns - Horseman's News
Dental issues in horses can certainly cause some of the symptoms that you describe. Fractured or infected teeth can cause poor appetite, difficulty chewing, and/or sinusitis (infected sinus) that would result in nasal discharge. They could also cause excessive salivation or bloody discharge from the mouth. However, the nasal discharge in these cases is more commonly only from one side, unless there are multiple teeth on both sides of the mouth that are affected.