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Reducing the risk of infection from purchased rams

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Purchasing stock and introducing it to your flock always carries the risk that infection can be brought in with them

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Marion McMilllan, veterinary investigation officer with SAC Consulting, says purchasing rams is no different and in spite of the fact they look in prime condition on the day of purchase they could be carrying some nasty surprises.

 

Mrs McMillan explains there are many infections and diseases which rams could be harbouring; Maedi Visna (MV), caseous lymphadenitis (CLA), Johne’s disease, Jaagsikete (also known as ovine pulmonary adenocarcinoma – OPA), Schmallenberg virus (SBV), sheep scab, lice, worms, fluke, footrot and contagious ovine digital dermatitis (CODD), to name a few.

 

And she adds quarantining new stock is essential to reduce problems in individual flocks.

 

“Quarantine facilities could be a building which is not shared by other animals or a field which is double fenced two metres apart, or just geographically separate from the other stock. A field with road or crops around it is ideal. It should be a field which is as dry as possible to prevent fluke infection and as midge free as possible,” says Ms McMillan.

 

“Quarantine treatments should be given on arrival to prevent the introduction of sheep scab, liver fluke and anthelmintic resistant worms to your farm.

 

“Rams should be kept away from the breeding flock for a minimum of four weeks to allow potential problems to develop and test results to be obtained. For some infections this is not long enough [see panel], but is a compromise to allow the use of the ram in the year of purchase.”

 

Mrs McMillan says if a ram is not MV-accredited two negative blood samples six months apart are required to be confident it is not carrying infection, the first one being when it is at least 12 months of age. This means using a non-accredited ram in the season it has been purchased is a potential risk. Whenever possible MV-accredited rams should be purchased to minimise the risk of infection to your flock.

Free from infection

For CLA two negative tests six weeks apart are needed to be reasonably confident the ram is free from infection.

 

“Johne’s disease should also be tested for. A blood sample or a faecal sample can be used to test for the disease. A positive result is usually reliable, while a negative result may mean the animal is still in the early stages of the disease and could eventually develop the disease. If animals have been vaccinated against Johne’s they are likely to test positive on the available blood tests so vaccination history should be checked with the seller before action is taken on a positive animal.

 

“OPA may also be carried by purchased rams and is an infectious lung tumour of sheep causing wasting and respiratory signs. Often animals will ultimately die due to bacterial pneumonia. Unfortunately, there are no commercially available tests to detect infection in clinically normal animals. Ultrasound examination of the lungs can be used to detect the lung tumours at an early stage.

 

As Schmallenberg virus has been found throughout the UK and Europe, Mrs McMillan says it would be wise to assume any purchased animal could come from an infected area.

 

“As infected animals clear the virus infection relatively quickly, any infected animals should be immune to disease by the time they come out of the quarantine area. Minimise the contact purchased animals have with midges by selecting the quarantine location carefully and consider treatment with a product containing deltamethrin to repel midges. Vaccination of the ewe flock could be considered to reduce the impact of infection.

 

“Ensure clostridial and pasteurella vaccinations are complete, if any doubt exists as to their status then restart the primary vaccination course.”

 

Mrs McMillan adds the time rams spend in quarantine facilities also allows close attention to be paid to the new rams. “The change of environment, flock, feeding and transport over a potentially considerable distance can result in problems, particularly pneumonia. Prompt treatment of any condition causing a raised temperature is essential as the raised temperature is highly damaging to sperm production. Feet should be checked regularly and any infections or problems treated promptly, this will prevent new infections being introduced to the flock.”

 

What are the diseases and what effects do they have?

Johne’s disease – bacterial infection. Young lambs are the most likely to become infected, but generally appear well until they are more than 18 months of age. Weight loss is the most common sign and unlike cattle many affected sheep do not show signs of scour. Infection can be passed between sheep, cattle and goats.

 

OPA – a viral infection which causes lung tumours. Animals with the disease show weight loss and if moving a group over a distance affected animals will fall behind the others and be short of breath. In the later stages of the disease fluid may be seen dripping from the nostrils. Also some animals may die suddenly as a result of secondary pasteurellosis and be in good body condition at the time of death.

 

MV – a viral condition which causes loss of condition, pneumonia, mastitis and arthritis. In some cases it can affect the nervous system causing ewes to drag a leg or become paralysed. As with OPA, the animals may die rapidly due to secondary pasteurellosis and this can complicate diagnosis.  

 

Affected sheep in thin body condition have reduced fertility. As the disease takes a long time to develop, affected sheep tend to be older.

 

Often by the time the disease becomes apparent more than half the stock are infected. Lambs from affected ewes are often born small or weak and fail to thrive as their dams have lower milk production. A recent survey conducted by SAC Consulting Veterinary Services with Animal Health and Veterinary Laboratories Agency showed 2.8 per cent (one in 35) of flocks have MV infection. This has doubled in the past 15 years.

 

CLA – a bacterial infection. The most obvious sign is the development of abscesses around the head and neck. In some cases these abscesses form on the internal organs and weight loss is the only outward indicator of a problem. Rams are more commonly affected than ewes, it is thought this is largely to do with rams being kept close together and also contact by fighting. 

 

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