Nasal discharge is detected during pen inspection. Discharges may be serous (thin, clear and colourless), catarrhal (grey, flocculent), purulent (thick, yellow), or haemorrhagic (red). A discharge may change in colour and consistency over time depending on the progression of underlying disease. Colour, consistency and content will often reveal the source. Presence of food or stomach content indicates obstruction of the oesophagus or gastrointestinal tract, respectively. This is generally accompanied by distress and severe systemic signs. Unilateral discharge indicates localised conditions involving the nose or sinuses, whereas bilateral discharge may indicate thoracic or systemic conditions.
The most likely differential diagnoses in shipboard cattle with nasal discharge include:
- Infectious bovine rhinotracheitis (IBR).
- Other respiratory pathogens (see Pneumonia).
- Dusty feed causing irritation of nasal mucosa or respiratory irritants such as ammonia. Ocular discharge, sneezing and coughing may be seen but animals will be bright, alert, appetant, afebrile and the nasal discharge may be heavily discoloured by dust. Examination of the feed will assist diagnosis.
- Systemic illness (sick cattle). Sick cattle tend to accumulate nasal secretions in the nares because they stop normal grooming behaviour, where the tongue is used to groom the nose. Abnormal nasal secretions may therefore be a generic sign of any underlying systemic disease.
- Oesophageal or gastrointestinal obstruction may cause reflux to appear at the nares.
In sheep and goats, common causes of discharge in multiple animals include nasal bots, dusty feed, ammonia vapour, fly worry, and upper respiratory tract infections due to viruses or bacteria. Fly worry will occur on land, and other causes may occur at all stages of the export process. When single animals are affected, differential diagnoses may include tumours, foreign bodies, and facial trauma distorting the nasal passages.
Differentiation may be assisted by the presence of other signs, such as sneezing, coughing, eye discharge, attempts to hide the face, and whether the discharge is unilateral or bilateral. Unilateral discharge usually indicates local involvement of one nasal passage. Bilateral discharge may indicate systemic disease affecting the upper respiratory tract. Close examination for the presence of mucus, pus, blood or foreign material may offer clues.