Equine case study - by Dave Rendle

An interactive case study involving a 7 y/o Thoroughbred cross mare with a 4 week history of coughing and bilateral serous nasal discharge where observations must be made. Complete with questions. For veterinary use.

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Equine case study - by Dave Rendle

History and Signalment

You are presented with a 7 year-old Thoroughbred cross mare with a 4 week history of coughing and bilateral serous nasal discharge. The horse has been in the owner’s possession for 3 years with no previous disease reported. The horse is vaccinated for influenza and tetanus, last performed 11 months ago. The horse is kept on a do-it-yourself livery yard in an American barn.


Physical examination

The horse is in good general body condition, with excessive fat deposits over the ribs and hindquarters. You note a unilateral right-sided mucoid nasal discharge. Rectal temperature is 39.3°C, heart rate 42 beats per minute and respiratory rate 16 breaths per minute. You do not detect any abnormalities on thoracic or tracheal auscultation. Lung sounds are audible over the entirety of both lung fields.


Clinical pathology

A mild increase in plasma fibrinogen concentration (4.1 g/l) is identified; however, serum amyloid A (SAA) concentration is within normal limits. An increase in serum gamma glutamyl transferase (GGT) concentration is also present (65 iu/L). Other serum proteins, liver enzymes, urea and creatinine are all within normal limits. Haematological examination does not reveal any abnormalities.

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  • The results of haematology and biochemistry indicate:

    1. The presence of infection
    2. An inflammatory response – hard to be any more specific
    3. An allergic disorder
    4. The presence of severe hepatic disease
  • What would you do next?

    1. Endoscopy to look at the upper and lower airways
    2. Endoscopy and a tracheal wash for cytology and culture
    3. Endoscopy, a tracheal wash for culture and a BAL for cytology
    4. Radiographic examination of the chest
  • The radiographic findings and results of lung washes are indicative of

    1. No disease being present
    2. A low-grade bacterial infection
    3. Inflammatory airway disease (IAD)
    4. Recurrent airway obstruction (RAO)
  • The radiographic changes would best be described as

    1. Normal
    2. An alveolar pattern
    3. A bronchial pattern
    4. A bronchointerstitial pattern
  • What will be the most important (if not exclusive) treatment for this horse?

    1. Antimicrobials
    2. Bronchodilators
    3. Glucocorticoids
    4. Non-steroidal anti-inflammatory drugs
  • Answers

    1. 2. The increase in one acute phase protein with others being normal and a normal leucogram is a non-specific and slightly equivocal finding. The mild increase in GGT is similarly equivocal and there are no other indicators of hepatic disease. Mild increases in acute phase proteins have been identified in some allergic conditions.
    2.  3. The presence of a cough indicates lower airway disease and the mild systemic inflammatory response would be consistent with this. Tracheal wash samples are useful for culture but have limited value for cytology. Cytology of a bronchoalveolar lavage sample would be the most appropriate means of diagnosing recurrent airway obstruction and inflammatory airway disease. The trachea contains grade 2/4 mucopus. Cytology performed on the bronchoalveolar lavage sample reveals 55% neutrophils, 36% macrophages, 7% lymphocytes and 2% eosinophils. Bacterial culture performed on the tracheal wash sample yields a moderate mixed growth of E.coli and Pseudomonas aeruginosa.
    3. 4. There are cytological and radiographic changes consistent with RAO. The cytological changes are consistent with this and the presence of clinical signs at rest precludes the possibility of IAD. The bacteria identified on the tracheal wash are not primary respiratory pathogens and are likely to be contaminants. Radiographic examinations are also performed given the high rectal temperature that would be not expected with a non-infectious lower respiratory tract disorder.
    4. 4. A bronchointerstitial pattern
    5. 3. Glucocorticoids. Recurrent airway obstruction is an allergic disorder and effective management will require good control of the environment and generally glucocorticoids to suppress the immune response. Bronchodilators may also be beneficial; NSAIDS will not. Treatment with antimicrobials should be avoided unless there is convincing evidence of secondary infection.

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