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Monday, 11 May 2015

Respiratory Disease in Adult and Yearling Sheep

Pasteurellosis
Mannheimia haemolytica is responsible for septicaemia in young lambs, pneumonia in older sheep and mastitis in ewes. It is therefore of significant economic importance to the sheep industry.
·         Clinical signs of Pasteurellosis: acute onset of depression, lethargy and inappetance, often segregation from the group. Affected sheep show increased respiratory rate with an abdominal component and a fever (>40.5).
·         Pathology: the lungs are heavy, swollen and purple-red in colour, sometimes containing blood-stained froth. Chronic cases show consolidation and fibrinous pleurisy.
·         Diagnosis: respiratory disease caused by M. haemolytica is based upon clinical signs; there is no confirming test in living sheep. Necropsy results can confirm the diagnoses – examining lung lesions and bacteriology.
·         Treatment: good treatment response to antibiotic therapy is reliant upon rapid detection of sick sheep. Oxytetracycline is the antibiotic used, as there are few antibiotic resistant strains in sheep.
·         Prevention/Control: prevention is best attempted using vaccines. Breeding ewes require a primary course of 2 injections 4 – 6 weeks apart, followed by an annual booster 4 – 6 weeks before lambing. However, this vaccination only provides passive immunity to the lambs for up to 5 weeks. Lambs can be protected by 2 doses of vaccine, given from 10 days-old.

Sheep Pulmonary Adenomatosis (SPA) (Jaagsiekte, ovine pulmonary adenocarcinoma OPA)
It is a common contagious tumour of the lungs of sheep in the UK, however is often not diagnosed because farmers rarely present sick sheep to the vet, believing all pneumonias have the same cause.
(Pneumonia is inflammation of the lungs caused by bacterial or viral infection; alveoli can fill with pus and often become blocked. Both sides (double) or just one side (single) infection of the lungs can occur) Disease transmission is facilitated by close confinement and has presented as most damaging in systems where sheep are housed for long periods during winter months.
·         Clinical presentation:  In naturally infected sheep, incubation period is long, with clinical disease apparent in 2 – 4 year-old sheep; in progeny of infected sheep, disease is seen 8 – 12 months after birth. Early clinical signs include loss of body condition and exercise intolerance, manifested as a markedly increased respiratory rate and brief periods of mouth breathing (panting). Appetite remains good. As the disease progresses, affected sheep have an obvious abdominal component to their breathing. Fluid gathers in the respiratory tract, which first appears as nasal discharge when the head is lowered. If the rear legs are raised, large volumes of fluid run out of the nose and mouth. A soft cough is often audible.
Death may follow a brief illness manifest as profound depression, inappetance and pyrexia; secondary to infection of the comprised lung with M. haemolytica. Antibiotic treatment of such secondary bacterial infection often results in temporary improvement but affected sheep must be culled as they are a source of infection for other groups.
·         There is no treatment. Infection is introduced to flocks by purchased sheep. There is no test for the disease; diagnosis is always confirmed at necropsy. The main route of infection is by respiratory aerosol with housing and trough feeding increasing the rate of spread. Offspring of infected sheep should never be placed into disease-free flocks.

Atypical pneumonia
A non-progressive chronic pneumonia of housed sheep under a year-old caused by Mycoplasma ovipneumoniae, and possibly other organisms (Parainfluenza 3 virus and Chlamydia psittaci). The true prevalence of the disease is unknown because clinical signs are mild and do not generally warrant further investigation.
·         Clinical presentation: the significant clinical finding is one of slightly reduced growth rate despite an appropriate ration. A chronic soft cough and nasal discharge spreads slowly through the group most noticeable when suddenly disturbed.
·         Pathology: lung changes are usually only detected at the abattoir and consist of red-brown or grey collapsed areas in the apical and cardiac lobes.
·         Treatment: is generally not necessary because clinical signs are mild. Oxytetracycline should be given to sick lambs which are not eating.
·         Prevention/Control: control can be attempted by improving ventilation and reducing stocking density. The airspace should not be shared with older sheep. Prevent purchased lambs from being housed with homebred stock.

Parasitic Bronchitis
Lungworm may cause coughing and weight loss in heavy infestations but this is very uncommon. Relative to PGE, lungworm infestation is of no economic significance to sheep farmers.
Treatment for lungworm is not necessary as their control can effectively be achieved by regular anthelmintic treatments used in the management of PGE. Severe lungworm infestations are often seen in sheep with Paratuberculosis (John’s disease) due to compromise of the immune system.

Chronic Suppurative Pneumonia/Lung Abscesses
Lung abscesses are very common in nature in mature rams but are difficult to identify by inspection alone and vet investigation is essential to establish an accurate diagnosis. Chronic respiratory disease is a very important disease in breeding rams which is all too frequently overlooked or treated incorrectly.
·         Clinical presentation: sheep with significant chronic lung lesions present with a history of weight loss although appetite may appear normal. The rectal temperature is often slightly elevated (up to 40C). At rest, affected sheep have a higher respiratory rate compared to normal sheep, and cough occasionally. There may be an occasional purulent nasal discharge.
·         Treatment: As the patient is usually a breeding ram, veterinary examination is important. Penicillin is the antibiotic of choice for chronic respiratory disease. A 3 – 4 week treatment regime for treating valuable breeding stock with multiple pleural and superficial lung abscesses identified by ultrasonographic examination has produced encouraging results. A single long-acting injection of Oxytetracycline will not work.

·         Prevention/Control: the common finding of lung abscesses in mature rams is probably related to long periods of housing after birth and during their first winter. Viral infections are common during such periods, and such lesions may become infected with bacteria causing abscesses. Failure to recognise and treat early lesions allows these abscesses to grow into significant structures. 


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