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This article was published in 2002
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DD Salmon, District Veterinarian, Riverina Rural Lands Protection Board

1,464 2 to 4 year old merino wethers bought from Jundah, Qld (between Longreach and Windoura).


22 March 2002 Purchased
23 March 2002 Delivered Deniliquin in one road train.
Paddocked on an oat stubble running onto the Edward River
7 April 2002 Mustered in the late afternoon
8 April 2002 Drafted and drenched with Abamectin. Two different batches of drench were used, two different, experienced stockmen administered the drench with two new drenchguns. The sheep were held overnight.
9 April 2002 Paddocked onto two different paddocks, one a wheat stubble, one a pasture paddock the owner observed some diarrhoea before he let the sheep out of the yards.
14 April 2002 The owner observed almost the entire flock scouring and large numbers dead.
14 April-15 May Investigations by practitioner and DV
1 May 2002 Shorn, then put out into a different paddock
13 May 2002 800 dead, the balance starting to look better, but still down in condition and lacking energy.

Clinical Observations

The primary clinical syndrome was diarrhoea and wasting. There were very few sheep not affected (<50/1464).

Over a 4 week period more than half of the affected flock died. Typically they became weak, went down in sternal recumbency and died.

Field Observations

The paddock that the sheep were run in prior to drenching was an oat stubble with a fair green pick. The paddock ran down to the Edward River with a few shrubs and dry grasses. There was one small patch of nardoo (about 10m square) under a tree.

The paddocks into which the sheep were put on 9/4/02 were:

1. A wheat stubble with a lot of green self-sown wheat and some Scotch thistles and Paterson's curse.

2. A dry pasture paddock with dry grass, some green grass, more Paterson's curse than the wheat stubble and an occasional dock plant.

Post Mortem Observations

Autolysis tended to be quicker than expected. There was some fibrinous fluid, with or without fibrin clots in some of the serosal cavities.

In some carcasses the kidneys were congested and severely autolysed. There was generally severe gastroenteritis, in the chronic cases it tended to localise in the large intestine and particularly the caecum.

Laboratory Findings

Generally unrewarding. No pathogenic organism was isolated. In one autolysed kidney sample there was a suggestion of crystals, possibly oxalate, this observation was repeated in a better preserved kidney, but the pathology associated with it was not severe.

In the more chronic cases the gastrointestinal changes were reported as being consistent with bacterial infection:

o Q Cystic abscessated crypts.

o Superficial congestion.

o Widespread predominantly non-suppurative infiltrate.

o Some foci in lamina propria.

o Polymorphs towards tips of villi.


No definite diagnosis has been achieved.

The fact that the sheep were moved to different paddocks after being handled and drenched indicates that whatever went wrong had its origin before then. There was nothing in any of the paddocks in which the sheep were running that could cause a toxic episode in a significant number of sheep.

None of the common bacterial agents that could be associated with this clinical syndrome could be detected on repeated attempts. The fact that 100% or very close to 100% of a large mob was affected is a unique feature of this episode.

An epidemic caused by an infectious agent is highly unlikely to reach that proportion. It is unlikely that every animal would come into contact with the infection. Of animals that do come into contact with the infection not all become infected and not all infected animals become sick.

The mortality rate of 55% is also unprecedented.

The pathologist commented that the gastrointestinal changes seen in the animal autopsied on 7 May looked bacterial. However no bacterial agent was detected.

Dr Janet Berry, District Veterinary Officer, Longreach, Qld spoke to the owner of the property of origin. The property was severely drought affected but reported few losses in the sheep remaining on the property during shearing.

It is almost certain that this episode is a result of the act of handling and drenching the sheep on 7-9 April.

The precise cause remains unknown.


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