Recent expansion of the sheep industry has triggered a resurgence of interest in managing disease in these animals.
Disease of the respiratory system is a major cause of death and production-limiting illness in sheep.
There are two main diseases of the nasal cavity and sinuses in sheep:
- Nasal bots — Infection occurs when flies deposit eggs in the nostrils, which hatch into the larval form. Upon reaching maturity in several months, the larvae exit the nasal cavity and continue their development into flies in the ground. Infection is associated with nasal discharge, coughing and sneezing.
Deworming is useful for controlling this infection. Dogs and humans who have close contact with sheep can also become infected with these nasal bots, although this is thought to be rare.
- Nasal tumours — These tumours can occur spontaneously in sheep, or in the case of enzootic nasal adencarcinomas, are induced by a virus infection. Mature sheep are most often affected.
Clinical signs include nasal discharge, difficulty breathing or sneezing. Tumours of the nasal cavity are usually diagnosed during autopsy examination, but facial deformity can result from the growth and invasion of particularly large nasal tumours.
- Pneumonia (lung inflammation) can be caused by a variety of viruses, bacteria, parasites or toxins.
Viral pneumonia in lambs is linked to a group of viruses similar to bovine pneumonia, including adenovirus and parainfluenza virus 3. Unless a secondary bacterial infection occurs, most viral pneumonias are mild and self-limiting.
Ovine progressive pneumonia is a viral pneumonia that affects mature animals. Caused by ovine lentivirus, which is related to human and feline immunodeficiency viruses, this pneumonia affects all portions of the lungs.
Abnormal white blood cells accumulate in the blood vessels where air exchange occurs. Clinical signs in affected sheep include difficulty breathing and poor body condition. No treatment is available and death is inevitable.
Sheep have their own species of lungworms, and appropriate de-worming protocols and pasture management to minimize parasite transmission are important for managing the impact of these infections.
Certain types of bacteria are always present in the upper respiratory tract of healthy sheep, but bacterial pneumonia can develop in times of stress or viral infection.
Mannheimia and related bacteria are an important cause of sheep feedlot pneumonia.
Affected sheep become ill rapidly, have difficulty breathing, cough and develop a fever. Surviving lambs may develop chronic lung abscesses and adhesions between the lung and inner rib cage.
Mycoplasma ovipneumoniae’s role in sheep pneumonia is not entirely clear. Mycoplasmas in many other species impair the normal defense mechanisms of the upper respiratory tract.
In health, microscopic cilia (small, finger-like projections) move mucous and debris up the trachea to the mouth where it can be swallowed.
Mycoplasmas stop this normal motion, resulting in accumulation of mucous and debris in the lungs and setting up a perfect environment for bacteria to grow and cause pneumonia.
Recent deaths of big horned sheep in the United States and Canada have been associated with mycoplasma, and there has been speculation that domestic sheep are responsible for introducing the bacteria into these populations.
Respiratory disease can be diagnosed based on physical examination findings, including listening to lung sounds with a stethoscope.
In live animals, samples of mucous and fluid from the lungs can be cultured to identify the problem bacteria and help determine management decisions.
An autopsy can examine the trachea and lungs in outbreak or feedlot settings, and microscopic examination of tissues and bacterial culture can provide a diagnosis.
General factors that predispose sheep to respiratory disease include crowding, weather, indoor air quality and stress, such as weaning, shipping and mixing groups.
Labelled respiratory vaccines for sheep are not available in Canada. Antibiotic treatment should be given under the direction of a veterinarian and appropriate withdrawal times considered for those animals destined for slaughter.
Farmers who are concerned about respiratory disease in their flocks should consult their veterinarian to develop a management plan.
Dr. Jamie Rothenburger is a veterinary pathology resident at the Western College of Veterinary Medicine, University of Saskatchewan.