The prevalence of ovine pulmonary adenocarcinoma (OPA) is becoming an increasing problem within sheep flocks of all breeds. Raising awareness of the disease was the key focus at a recent workshop held at CAFRE’s Hill Farm sheep unit in Northern Ireland.
OPA, or Jaagseikte, is a virus which affects the lungs of sheep, causing cancerous tumours to develop and leads to higher mortality levels.
Other symptoms include animals wasting away and the increased incidence with secondary respiratory problems such as pasturella pneumonia.
Infected sheep will often have a persistent cough, or discharge coming from the mouth and nasal cavities.
Misdiagnosis
According to Jason Barley, from the Agri Food and Bioscience Institute (AFBI), a big problem in controlling OPA is that it is often misdiagnosed.
The disease causes secondary infections, which are easier to identify and often assumed to be the solitary cause of any illness or mortality.
While secondary infections will lead to the death of animals, there is seldom any exploratory investigation undertaken to find the origins of such persistent problems. More often than not, these issues stem from the presence of OPA in flocks.
Barley said that the prevalence of OPA in sheep presented to AFBI veterinary labs for post-mortem has increased year on year.
In 2012, OPA was the cause of death in 2.2% of all sheep presented for post-mortem. This has grown to 3.8% this year.
The traditional view is that OPA is a problem solely in hill sheep, mainly Blackface animals
While numbers initially appear small, Barley said this is just the tip of the ice-berg, as the disease is widespread across Northern Ireland, with a lot still to be learned about how it develops in sheep.
The traditional view is that OPA is a problem solely in hill sheep, mainly Blackface animals. However, Barley said this is not the case, as lowland breeds are also being affected.
He added that the disease is becoming a growing problem within flocks where lambs are housed for finishing, with animals more prone to developing mycoplasma problems.
Late symptoms
Diagnosing the problem in live sheep can only be determined through ultrasound scanning. As little is known about the causes of OPA, there is no blood test available. As such, there is no prospect of a vaccine coming on to the market in the near future.
If ewes are slow to gain body condition when grazing conditions are favourable, and following a proper health plan for parasites, they should be viewed as suspect animals for OPA
Normal symptoms can be slow to surface, often taking anywhere from one to three years to materialise. By this stage, infected animals may have transmitted the virus throughout the flock.
Therefore, sheep farmers should be alerted to the presence of thin animals within flocks. If ewes are slow to gain body condition when grazing conditions are favourable, and following a proper health plan for parasites, they should be viewed as suspect animals for OPA and marked for immediate culling.
Ewe lambs bred from these suspect animals should not be retained for breeding, as they are highly likely to keep transmitting the virus within the flock.
Patrick Grant is a vet who specialises in working with sheep and, at the open day, he demonstrated how ultrasound scanning can be used to detect early signs of tumours developing in sheep.
Grant has been using the scanner in NI flocks over the last four years. He said that, on average, flocks scanned have around 5% to 6% of breeding ewes being confirmed as positive with OPA. The highest incidence scanned was 10%, with a low of 2%.
Within the test group scanned during the demonstration, there were several ewes in excessive body condition
As there is no treatment for the disease, the natural outcome is higher mortality in breeding flocks, which is an economic loss to farmers. More dead ewes means that additional replacements have to be purchased.
Within the test group scanned during the demonstration, there were several ewes in excessive body condition.
Visually, these animals appeared healthy, but the scanner confirmed the presence of small tumours in the lungs.
Early detection
Grant said that, in most cases, farmers would assume these animals are OK to continue breeding into next year again, based on visual appearance.
However, as the tumours grow, the ewes will pine and lose flesh. Fertility and maternal abilities are also affected, meaning higher barren rates.
Early detection of the tumours allows farmers to cull these animals early while in good body condition, maximising sale values and helping to cover replacement costs.
Scanning costs approximately £2/head (€2.27), while the differential in cull values between fleshed and thin ewes can be as much as £60 per herd (€68) in mature animals.
Ranking sheep
When scanning sheep, they are then split into four groups as follows:
Group one – healthy sheep.Group two – healthy sheep but test unclear. Separate and rescan animals.Group three – thin sheep, separate and rescan at later date.Group four – positive OPA.Grant said that group four animals should be culled immediately, as there is no benefit to holding on to these animals.
Group three is generally animals that are thin, but may be too early to confirm as a positive case. These animals should be treated as highly suspicious and marked for culling or separating and re-scanning.
Control steps
He added that when it comes to OPA, there is a need for an open and frank debate on the topic, as every farmer has a responsibility to help control the disease, with eradication not being an option.
Sheep purchased as breeding replacements, or rams, should be isolated and scanned before joining the main flock.
The ideal time to carry out scanning is in summer and mid-pregnancy
Similarly, breeders should view scanning as a way to build a market of repeat buyers by selling healthy sheep.
The ideal time to carry out scanning is in summer and mid-pregnancy. Contrary to some opinions, scanning for OPA is taking a pro-active approach to flock health, similar to controlling foot rot and other diseases.
If animals have a positive scan, there is no requirement to notify Department officials. OPA is only a notifiable disease after confirmation from a lab diagnosis.
Putting the ultrasound scanning into practice
The sheep flock at CAFRE’s Hill Farm has been scanned for OPA since 2017, as there had been a growing prevalence of sheep displaying symptoms and an awareness of the links to hill sheep.
These symptoms included increasing numbers of thin sheep in the flock, which had to be separated for priority grazing.
While mortality levels were unaffected, the flock’s management team decided to scan animals as a proactive approach and to confirm or eliminate the presence of the disease on farm.
After scanning, around 3.2% of suspected ewes had a positive diagnosis. But with other suspect animals in the flock, 8% of animals were culled.
Prior to scanning, there was a high incidence of pneumonia in adult sheep, along with breeding females scanning empty after tupping
Scanning has been carried out twice annually since 2017 and the culling policy is working. Earlier this year, scanning results fell to 2% of the flock being positive for OPA, a 1.2% drop in 18 months.
Culling rates are now down to 5% for the whole flock, which extends to approximately 1,000 ewes.
Prior to scanning, there was a high incidence of pneumonia in adult sheep, along with breeding females scanning empty after tupping.
Flock fertility has improved since separating suspect animals started and scanning confirmed positive cases of the disease.
In addition to the CAFRE flock, other farmers speaking at the event and scanning sheep for OPA had 3.5% of their Mule flock confirmed with the disease, while 8.5% of lowland sheep were affected on the same farm. After culling positive animals, mortality at lambing was reduced by one third.
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The prevalence of ovine pulmonary adenocarcinoma (OPA) is becoming an increasing problem within sheep flocks of all breeds. Raising awareness of the disease was the key focus at a recent workshop held at CAFRE’s Hill Farm sheep unit in Northern Ireland.
OPA, or Jaagseikte, is a virus which affects the lungs of sheep, causing cancerous tumours to develop and leads to higher mortality levels.
Other symptoms include animals wasting away and the increased incidence with secondary respiratory problems such as pasturella pneumonia.
Infected sheep will often have a persistent cough, or discharge coming from the mouth and nasal cavities.
Misdiagnosis
According to Jason Barley, from the Agri Food and Bioscience Institute (AFBI), a big problem in controlling OPA is that it is often misdiagnosed.
The disease causes secondary infections, which are easier to identify and often assumed to be the solitary cause of any illness or mortality.
While secondary infections will lead to the death of animals, there is seldom any exploratory investigation undertaken to find the origins of such persistent problems. More often than not, these issues stem from the presence of OPA in flocks.
Barley said that the prevalence of OPA in sheep presented to AFBI veterinary labs for post-mortem has increased year on year.
In 2012, OPA was the cause of death in 2.2% of all sheep presented for post-mortem. This has grown to 3.8% this year.
The traditional view is that OPA is a problem solely in hill sheep, mainly Blackface animals
While numbers initially appear small, Barley said this is just the tip of the ice-berg, as the disease is widespread across Northern Ireland, with a lot still to be learned about how it develops in sheep.
The traditional view is that OPA is a problem solely in hill sheep, mainly Blackface animals. However, Barley said this is not the case, as lowland breeds are also being affected.
He added that the disease is becoming a growing problem within flocks where lambs are housed for finishing, with animals more prone to developing mycoplasma problems.
Late symptoms
Diagnosing the problem in live sheep can only be determined through ultrasound scanning. As little is known about the causes of OPA, there is no blood test available. As such, there is no prospect of a vaccine coming on to the market in the near future.
If ewes are slow to gain body condition when grazing conditions are favourable, and following a proper health plan for parasites, they should be viewed as suspect animals for OPA
Normal symptoms can be slow to surface, often taking anywhere from one to three years to materialise. By this stage, infected animals may have transmitted the virus throughout the flock.
Therefore, sheep farmers should be alerted to the presence of thin animals within flocks. If ewes are slow to gain body condition when grazing conditions are favourable, and following a proper health plan for parasites, they should be viewed as suspect animals for OPA and marked for immediate culling.
Ewe lambs bred from these suspect animals should not be retained for breeding, as they are highly likely to keep transmitting the virus within the flock.
Patrick Grant is a vet who specialises in working with sheep and, at the open day, he demonstrated how ultrasound scanning can be used to detect early signs of tumours developing in sheep.
Grant has been using the scanner in NI flocks over the last four years. He said that, on average, flocks scanned have around 5% to 6% of breeding ewes being confirmed as positive with OPA. The highest incidence scanned was 10%, with a low of 2%.
Within the test group scanned during the demonstration, there were several ewes in excessive body condition
As there is no treatment for the disease, the natural outcome is higher mortality in breeding flocks, which is an economic loss to farmers. More dead ewes means that additional replacements have to be purchased.
Within the test group scanned during the demonstration, there were several ewes in excessive body condition.
Visually, these animals appeared healthy, but the scanner confirmed the presence of small tumours in the lungs.
Early detection
Grant said that, in most cases, farmers would assume these animals are OK to continue breeding into next year again, based on visual appearance.
However, as the tumours grow, the ewes will pine and lose flesh. Fertility and maternal abilities are also affected, meaning higher barren rates.
Early detection of the tumours allows farmers to cull these animals early while in good body condition, maximising sale values and helping to cover replacement costs.
Scanning costs approximately £2/head (€2.27), while the differential in cull values between fleshed and thin ewes can be as much as £60 per herd (€68) in mature animals.
Ranking sheep
When scanning sheep, they are then split into four groups as follows:
Group one – healthy sheep.Group two – healthy sheep but test unclear. Separate and rescan animals.Group three – thin sheep, separate and rescan at later date.Group four – positive OPA.Grant said that group four animals should be culled immediately, as there is no benefit to holding on to these animals.
Group three is generally animals that are thin, but may be too early to confirm as a positive case. These animals should be treated as highly suspicious and marked for culling or separating and re-scanning.
Control steps
He added that when it comes to OPA, there is a need for an open and frank debate on the topic, as every farmer has a responsibility to help control the disease, with eradication not being an option.
Sheep purchased as breeding replacements, or rams, should be isolated and scanned before joining the main flock.
The ideal time to carry out scanning is in summer and mid-pregnancy
Similarly, breeders should view scanning as a way to build a market of repeat buyers by selling healthy sheep.
The ideal time to carry out scanning is in summer and mid-pregnancy. Contrary to some opinions, scanning for OPA is taking a pro-active approach to flock health, similar to controlling foot rot and other diseases.
If animals have a positive scan, there is no requirement to notify Department officials. OPA is only a notifiable disease after confirmation from a lab diagnosis.
Putting the ultrasound scanning into practice
The sheep flock at CAFRE’s Hill Farm has been scanned for OPA since 2017, as there had been a growing prevalence of sheep displaying symptoms and an awareness of the links to hill sheep.
These symptoms included increasing numbers of thin sheep in the flock, which had to be separated for priority grazing.
While mortality levels were unaffected, the flock’s management team decided to scan animals as a proactive approach and to confirm or eliminate the presence of the disease on farm.
After scanning, around 3.2% of suspected ewes had a positive diagnosis. But with other suspect animals in the flock, 8% of animals were culled.
Prior to scanning, there was a high incidence of pneumonia in adult sheep, along with breeding females scanning empty after tupping
Scanning has been carried out twice annually since 2017 and the culling policy is working. Earlier this year, scanning results fell to 2% of the flock being positive for OPA, a 1.2% drop in 18 months.
Culling rates are now down to 5% for the whole flock, which extends to approximately 1,000 ewes.
Prior to scanning, there was a high incidence of pneumonia in adult sheep, along with breeding females scanning empty after tupping.
Flock fertility has improved since separating suspect animals started and scanning confirmed positive cases of the disease.
In addition to the CAFRE flock, other farmers speaking at the event and scanning sheep for OPA had 3.5% of their Mule flock confirmed with the disease, while 8.5% of lowland sheep were affected on the same farm. After culling positive animals, mortality at lambing was reduced by one third.
Read more
Farmer Writes: stress levels up with grass down
Factories ‘lining their pockets’ with sheep price cuts
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