Sneaky Sheep Lungs!

Postmortem examination of thin cull ewes is an effective way to investigate whether Iceberg diseases such as Johne’s disease, ovine pulmonary adenocarcinoma (OPA) or maedi visna (MV) are present in a flock. This can be carried out very successfully on farm, however one potential pitfall is the misdiagnosis of lung lesions based on gross examination alone. To illustrate this, here are a three examples from a ewe screen carried out in Aberdeen – see what you think!

_{Ewe 1.}

_{Ewe 2.}

_{Ewe 3.}

What were your gross diagnoses?

Following serological testing and histopathology of fixed tissues, the following diagnoses were reached:

• Ewe 1:  OPA and Maedi Visna
• Ewe 2:  Maedi Visna
• Ewe 3:  Maedi Visna and pulmonary abscessation

Histopathology confirmed that ewe 1 did indeed have OPA, but surprisingly ewe 2 did not.  All of the ewes had histopathological changes consistent with MV and tested positive for MV on serology. 

Hopefully it’s apparent that gross diagnosis of lung lesions can be challenging, even for experienced VIO’s. In the field, misdiagnosis has the potential to have a significant and long-lived financial impact for the farmer.  This particularly applies to identifying the presence of OPA and/or MV on a farm, which carry very different implications for flock management and profitability, therefore accurate diagnosis is essential. 

Histopathology (+/- MV serology) is essential to diagnose lung disease in sheep. To maximise the likelihood of reaching a diagnosis from submitted lung, we offer the following tips:

• Avoid crushing the samples:
• sample the lung before vigorous palpation.
• avoid the use of forceps on sampled tissue.
• use a sharp knife or new scalpel blade for cutting.
• Small samples of 1cm x 1cm x 2cm are perfect.
• Fix the sampled tissues in 10x their volume of formalin.
• Drain the formalin from fixed tissues before sending in leak proof packaging.

SRUC Vet Services are always interested to look at images from PMs via WhatsApp or email, although it’s likely we will suggest some histopathology.

Posted by SRUC Veterinary Services on 19/03/2025