A number of the farmer focus introductory articles of recent weeks had a common health theme of aiming to address ovine pulmonary adenocarcinoma (OPA) or Jaagsiekte sheep retrovirus, as it is also commonly known. This has generated reader queries as to how farmers are planning to achieve this objective and why it is being held as high priority.
To recap on the importance, the disease is often best described as being likened to cancer of the lungs, causing significant respiratory issues and eventual mortality in affected animals. It can advance at different rates and generally has an incubation period of three years, but industry views indicate that this can range anywhere from two months to 11 years, depending on the severity of the infection.
Characteristic symptoms are sheep possessing a soft cough in the early stages of the disease. As the infection advances, sheep struggle to keep pace with other sheep when flocked and can exhibit a frothy fluid discharge from their nostrils in the later stages of the disease. It is often raised as a greater issue in hill flocks but research shows it is also present in lowland flocks.
A secondary bacterial pneumonia can also develop and is more common in flocks with a significant disease rate. The virus is easily spread through respiratory aerosol (passes through the air), contaminated feeding equipment and also to progeny via colostrum. The disease is believed to be significantly under-reported with poor-performing ewes frequently culled and low levels of post mortems taking place. Hence, it is an important ailment to address.
Disease identification
The low level of identification is also complicated by the disease showing no immune response and the lack of a commercially available diagnostic blood test.
A physical test known as the wheelbarrow test can help to identify advanced cases but this test is not recommended without veterinary intervention where sheep can be euthanised as it causes distress.
One of the best options at present to identify OPA in live sheep is thoracic ultrasound scanning to identify the presence of lesions/tumours on the surface of lungs. This method has its limitations with lesions of greater than 2cm required to denote its presence.
The presence of lung abscesses can also complicate its identification but those carrying out the scanning are becoming more accomplished as they move through higher numbers and can now differentiate between both.
Therefore scanning is the only realistic option available for testing live sheep and along with post-mortem diagnosis of suspect fallen animals is the avenue being utilised through the Northern Ireland Sheep Programme.
Three vets have carried out testing across eight of the 10 participating farms in the programme. They are Patrick Grant, The Sheep Vet; Rachel Harkness, Riada Veterinary Clinic and Noel Doyle, Three Valleys Veterinary. There are other vets trained in the practice and it is worth consulting with your own vet if progressing down the route of scanning.
It is worth also pointing out that work is also taking place in the Greenmount flock and is linked in with AFBI research assessing the accuracy of ultrasound scanning.
Scanning procedure
Scanning takes place behind the sheep’s shoulders at the non-wool area. The animal’s front legs are raised upwards, allowing the lungs to be carefully examined.
The vets carrying out the scanning are trained to pick up any damage in the lungs and areas of growth. Sheep are generally classified into three categories – confirmed cases, suspect cases and healthy animals.
Suspect cases are highlighted for repeat scanning with the timeframe influenced by the rate of infection on the farm. For example, where there are significant issues identified, repeat scanning will generally take place quicker. In such cases, it may be prudent for farmers to cull suspect animals for slaughter and this decision will be based on farm circumstances, the stage of the season and veterinary advice.
Where there is a low level of suspect cases, repeat scanning may take place after a longer interval.
Programme results
As already mentioned, eight of the 10 participating farms have carried out testing to date. OPA has been identified on six of these farms with hill flocks to date recording a higher prevalence and two out of three lowland flocks showing up clear of the disease. The other two flocks will carry out testing in the coming months.
Where OPA has been identified, typical rates of positive identification are 2% to 3% with one case rising to 8% in a particular batch of sheep on one farm. This shows how the problem can spread and become a significant cause of poor performance and mortality.
A full analysis of results will be detailed when available at a later stage while programme events held this year will also provide information on OPA. Scanning typically costs from £1.60/animal (€1.84) to £2/animal (€2.30) with numbers on offer influencing costs.
The typical OPA signs of weight loss and increased respiratory effort after exercise and at rest could apply to many other diseases. Post mortem examination of the lungs is necessary for disease confirmation.
A critical aspect in getting on top of issues is to now implement a robust biosecurity protocol as part of the farm’s health programme as there is little point in going to the trouble and expense of scanning if it will not be acted upon.
The majority of flocks are changing to breeding replacements from within the flock and only purchasing replacements from sources where they can have a degree of confidence in doing so. In the longer term, there is potential for farmers to produce high-health status replacements for sale from accredited flocks.
Adviser comment: Senan White
“There has been good uptake from all participating farmers. Hill farmers, in particular, are keen to get to the bottom of relatively high barren rates and want to investigate if OPA is linked to below-par performance in this area while also getting a better understanding of the causes of ewe mortality.
“OPA is a big challenge for the sheep industry with relatively little known about the disease. The programme is working closely with best practice advice based on research in this area and hopefully it can demonstrate the benefits of tackling problems at farm level”.
A number of the farmer focus introductory articles of recent weeks had a common health theme of aiming to address ovine pulmonary adenocarcinoma (OPA) or Jaagsiekte sheep retrovirus, as it is also commonly known. This has generated reader queries as to how farmers are planning to achieve this objective and why it is being held as high priority.
To recap on the importance, the disease is often best described as being likened to cancer of the lungs, causing significant respiratory issues and eventual mortality in affected animals. It can advance at different rates and generally has an incubation period of three years, but industry views indicate that this can range anywhere from two months to 11 years, depending on the severity of the infection.
Characteristic symptoms are sheep possessing a soft cough in the early stages of the disease. As the infection advances, sheep struggle to keep pace with other sheep when flocked and can exhibit a frothy fluid discharge from their nostrils in the later stages of the disease. It is often raised as a greater issue in hill flocks but research shows it is also present in lowland flocks.
A secondary bacterial pneumonia can also develop and is more common in flocks with a significant disease rate. The virus is easily spread through respiratory aerosol (passes through the air), contaminated feeding equipment and also to progeny via colostrum. The disease is believed to be significantly under-reported with poor-performing ewes frequently culled and low levels of post mortems taking place. Hence, it is an important ailment to address.
Disease identification
The low level of identification is also complicated by the disease showing no immune response and the lack of a commercially available diagnostic blood test.
A physical test known as the wheelbarrow test can help to identify advanced cases but this test is not recommended without veterinary intervention where sheep can be euthanised as it causes distress.
One of the best options at present to identify OPA in live sheep is thoracic ultrasound scanning to identify the presence of lesions/tumours on the surface of lungs. This method has its limitations with lesions of greater than 2cm required to denote its presence.
The presence of lung abscesses can also complicate its identification but those carrying out the scanning are becoming more accomplished as they move through higher numbers and can now differentiate between both.
Therefore scanning is the only realistic option available for testing live sheep and along with post-mortem diagnosis of suspect fallen animals is the avenue being utilised through the Northern Ireland Sheep Programme.
Three vets have carried out testing across eight of the 10 participating farms in the programme. They are Patrick Grant, The Sheep Vet; Rachel Harkness, Riada Veterinary Clinic and Noel Doyle, Three Valleys Veterinary. There are other vets trained in the practice and it is worth consulting with your own vet if progressing down the route of scanning.
It is worth also pointing out that work is also taking place in the Greenmount flock and is linked in with AFBI research assessing the accuracy of ultrasound scanning.
Scanning procedure
Scanning takes place behind the sheep’s shoulders at the non-wool area. The animal’s front legs are raised upwards, allowing the lungs to be carefully examined.
The vets carrying out the scanning are trained to pick up any damage in the lungs and areas of growth. Sheep are generally classified into three categories – confirmed cases, suspect cases and healthy animals.
Suspect cases are highlighted for repeat scanning with the timeframe influenced by the rate of infection on the farm. For example, where there are significant issues identified, repeat scanning will generally take place quicker. In such cases, it may be prudent for farmers to cull suspect animals for slaughter and this decision will be based on farm circumstances, the stage of the season and veterinary advice.
Where there is a low level of suspect cases, repeat scanning may take place after a longer interval.
Programme results
As already mentioned, eight of the 10 participating farms have carried out testing to date. OPA has been identified on six of these farms with hill flocks to date recording a higher prevalence and two out of three lowland flocks showing up clear of the disease. The other two flocks will carry out testing in the coming months.
Where OPA has been identified, typical rates of positive identification are 2% to 3% with one case rising to 8% in a particular batch of sheep on one farm. This shows how the problem can spread and become a significant cause of poor performance and mortality.
A full analysis of results will be detailed when available at a later stage while programme events held this year will also provide information on OPA. Scanning typically costs from £1.60/animal (€1.84) to £2/animal (€2.30) with numbers on offer influencing costs.
The typical OPA signs of weight loss and increased respiratory effort after exercise and at rest could apply to many other diseases. Post mortem examination of the lungs is necessary for disease confirmation.
A critical aspect in getting on top of issues is to now implement a robust biosecurity protocol as part of the farm’s health programme as there is little point in going to the trouble and expense of scanning if it will not be acted upon.
The majority of flocks are changing to breeding replacements from within the flock and only purchasing replacements from sources where they can have a degree of confidence in doing so. In the longer term, there is potential for farmers to produce high-health status replacements for sale from accredited flocks.
Adviser comment: Senan White
“There has been good uptake from all participating farmers. Hill farmers, in particular, are keen to get to the bottom of relatively high barren rates and want to investigate if OPA is linked to below-par performance in this area while also getting a better understanding of the causes of ewe mortality.
“OPA is a big challenge for the sheep industry with relatively little known about the disease. The programme is working closely with best practice advice based on research in this area and hopefully it can demonstrate the benefits of tackling problems at farm level”.
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