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An Intestinal Adenocarcinoma Causing Ascites and Death in a Merino Ewe

BR Watt (Central Tablelands Local Land Services) and Patrick Staples (Elizabeth Macarthur Agricultural Institute, Menangle)

Posted Flock & Herd August 2022


As has been mentioned previously on Flock and Herd, intestinal adenocarcinoma is a common tumour of older sheep, most often discovered at slaughter as an incidental finding (Shearer and Watt 2015). In clinical cases, weight loss and occasional ascites are usually the only findings (Maxie 2007, Radostits et al. 2007). In the experience of the first author, intestinal adenocarcinoma usually presents as emaciation, with ovine Johne's disease (OJD) an important differential.

This case, in a single mature merino ewe, presented as abdominal distension due to ascites.


A single mature merino ewe in a flock of 1000 ewes was noticed to have slowly developed abdominal enlargement. The ewe was initially assumed to be pregnant but as the abdomen continued to enlarge without udder development it became apparent that this change was an abnormality.

The ewe, a full-mouthed merino with six months’ wool was found dead and necropsied on 23 July 2021. The ewe was in fat score condition 1.5 with slightly pale mucous membranes and marked abdominal distension. An ascitic wave could be felt on palpation of the abdomen.

Image of sheep with swollen abdomen
Figure 1. Marked ascites in the affected ewe
Image of sheep post-mortem showing fluid in abdomen
Figure 2. The ascitic fluid released at necropsy


On opening the abdomen, approximately 10 litres of clear brown fluid were released (Figure 2). The lungs were compressed and there were multiple 2 mm diameter pink nodules on most peritoneal surfaces (Figure 3). There were sheets of firm white tissue within the mesentery.

Image of sheep post-mortem showing multiple small tumours in abdomen
Figure 3. Peritoneum of the affected ewe showing diffuse 2 mm tumours


Multifocally, serosal surfaces of the intestine, mesentery and omentum were infiltrated by anaplastic epithelial cells surrounded by a marked fibroplastic (scirrhous) response. The neoplastic epithelial cells were arranged singly and within clusters, irregular cords and acini. The cells showed moderate anisocytosis, coarse nuclear chromatin, and a moderate mitotic rate. Some of the cells contained mucus (resembling intestinal goblet cells). Clusters of neoplastic cells were present within lymphatics. Patchy infiltrates of lymphocytes were present. There were no significant findings in the lymph node and adrenal gland examined.

The histopathological diagnosis was that of a scirrhous intestinal adenocarcinoma with widespread metastasis throughout the peritoneum. Ascites was consistent with obstruction of serosal lymphatics by tumour emboli.


As mentioned in the 2015 case report (Shearer and Watt).

'McDonald et al. (1965) found that 0.4% of all sheep and 2% of sheep over 5 years of age had lesions consistent with intestinal adenocarcinoma on one property. A 1980 southern NSW abattoir survey found 3 sheep affected per 1,000 (0.272%), with a regional variation in rates of between 0.2% and 1.5%' (Ross 1980).

Differential diagnoses that should be considered in cases of wasting include OJD, malnutrition, chronic infections such as pneumonia or caseous lymphadenitis, hepatic disease, internal parasitism and fasciolosis. These differentials should be kept in mind even in OJD-infected flocks. Bush et al. (2006) found that up to one third of cases of wasting in OJD-infected flocks could be attributed to causes other than OJD.


  1. Shearer P and Watt BR, Intestinal adenocarcinoma in an emaciated first cross ewe. Posted on Flock and Herd March 2015. www.flockandherd.net.au
  2. Maxie, G., Ed. (2007).Jubb, Kennedy & Palmer's Pathology of Domestic Animals: 3-Volume Set, Elsevier Health Sciences
  3. Radostits, O. M., Gay, C. C., Hinchcliff, K. W. and Constable, P. D. (2007). Diseases caused by bacteria.Veterinary Medicine: A Textbook of the Diseases of Cattle, Sheep, Pigs, Goats, and Horses, Elsevier Saunders:920
  4. McDonald, J. W. and Leaver, D. D. (1965). Adenocarcinoma of the Small Intestine of Merino Sheep. Aust. Vet. J. 41(9): 269-271
  5. Ross, A. D. (1980). Small intestinal carcinoma in sheep. Aust. Vet. J. 56(1): 25-33
  6. Bush, R. D., Toribio, J. A. and Windsor, P. A. (2006). The impact of malnutrition and other causes of losses of adult sheep in 12 flocks during drought. Aust. Vet. J. 84(7): 254-260


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