Coughing, the forceful, noisy expulsion of air, is an important aspect of the respiratory defense system. Coughing helps clear particles, mucous and other foreign material from the trachea, throat and deeper airway passages. There are many underlying diseases and conditions that can cause an animal to cough, so it is necessary to get a complete history and physical examination before doing further diagnostics.
Coughing is an involuntary reflex but it can also be suppressed or done voluntarily. The nerve receptors that trigger coughing are quite numerous in the trachea and bronchi above the level of the bifurcation. There are other cough-stimulating receptors within and around the lung tissue itself. Many of the nerve receptors that stimulate coughing are irritant receptors and can be triggered by things such as dust, exposure to hot or cold air, pinching the trachea, ammonia gas, and inflammation with excessive mucous production. Importantly, coughing is also triggered and accompanied by bronchioconstriction.
Some of the more common causes of coughing in cattle include:
- Shipping fever
- Enzootic calf pneumonia
- Lungworm infection
- Chronic bacterial pneumonia
- IBR (Infectious Bovine Rhinotracheitis caused by Bovine Herpes Virus I)
- Mycoplasma Pneumonia
- Calf Diphtheria
- Esophogeal obstruction/ Choke
Diseases of the respiratory tract can make the cough receptors more sensitive. For example, viruses like IBR that affect the respiratory tract can make the cough receptors more sensitive to irritants like dust or cold air.
Evaluating the cause of a cough in cattle should begin with a thorough history to try and identify stressors, changes in the environment, exposure to disease, presence of a fever, and management practices. The vaccination status of animals is also an important consideration when considering infectious causes of coughing. It is also important to characterize the cough itself and identify factors such as the onset, duration, and frequency, relation to other events, and any improvement or deterioration. The cough should be characterized by its anatomical location (upper airway vs. lower airway), dry or wet, productive or non-productive. Coughs originating in the upper airway usually develop rapidly and are dry, hacking coughs that don’t produce mucous or pus. On the other hand, coughs originating in the lower airways are usually more chronic and tend to be softer and productive.
Other diagnostic techniques that can be employed to help identify the underlying cause of a cough include:
- Complete Blood Count: This test will often show non-specific findings, but it can help identify anemia associated with caudal vena cava syndrome due to rumenal acidosis and increased fibrinogen associated with inflammatory conditions
- Nasopharyngeal Swabbing: Taking a sample of the naspharyngeal mucous for cytologic evaluation and culture is used to confirm viral and bacterial infections of the upper airways.
- Endoscopic Examination: This technique allows one to evaluate the upper airways for mass lesions, anatomical abnormalities and the source of exudates.
- Tracheal Aspiration: A sample from the trachea can be used for bacterial culture when an infection of the lungs and surrounding tissue is suspected.
- Bronchioalveolar Lavage: This technique gives better samples than tracheal aspiration for cytologic evaluation. Gram stains of bacteria found can also help when choosing an antibiotic before culture results are back from the lab.
- Thoracocentesis: This technique is used in animals with evidence of effusive pleural disease. Collecting pleural fluid can be used for bacterial culture and cytology.
- Blood Gas Analysis: This test can be useful in animals with a history of coughing accompanied by respiratory distress or cyanosis. Blood gas analysis allows one to look at the arterial oxygen and carbon dioxide levels to assess respiration.
- Fecal Examination: A Baermann technique allows one to detect lungworm larvae within the feces.
- Radiographic Examination: Thoracic radiographs can help identify the pattern of lung disease as well as the response to treatment.
Preventing coughing in cattle primarily involves good management practices to prevent the many diseases and conditions that cause coughing. It is important to maintain a good vaccination and deworming protocol to help prevent infectious causes of coughing. Additionally, one should try to prevent stress such as shipping, crowding, extreme temperatures, and nutritional deficits. Finally, if an infectious cause of coughing is suspected, it is a good idea to quarantine the affected animals to prevent the spread of disease via aerosolized viral or bacterial particles.
Treating coughing should be tailored to the specific underlying disease condition associated with this symptom. In general, it is important to reduce stress in these animals, keep them warm and in an area that is well ventilated, and to provide good quality nutrition.
Smith, B.P. Large Animal Internal Medicine, 3rd Ed. Mosby-Elsevier Publishing. St. Louis, MO. 2009. pp.46-54.
Merck Veterinary Manual Online: http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/121200.htm