CASE NOTES

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Humpyback

Shaun Slattery, District Veterinarian, Narrabri RLPB

Posted Flock & Herd February 2011

History

Experience with this condition limited to sporadic cases seen in early 1990s (eg couple of affected ewes in whole flock at shearing) and series of cases late summer — autumn 1998 (wet summer). Three properties visited and animals examined and number of others reported by telephone.

Difficulty in investigating after the event (next day after shearing, crutching,etc. done). Greater experience is probably with other causes of staggers in this type of country. Locomotor syndrome of full-woolled sheep in summer and autumn. In western Queensland and North-Western NSW. Usually older sheep.

That it is full wool sheep would suggest a hyperthermia component and this has been recorded in affected sheep. Usually occurs a couple months after good spring-summer rains. Properties that get it often report that there are usually one or two cases per year but in certain years it is a larger problem.

Associated primarily with Solanum esuriale (Quena). Feeding trials have reproduced the disease after feeding and exercising in hot room. Other feeding trial of sheep sourced from outside known range of disease failed to produce disease.

In some seasons sheep will actively seek out and eat berries — in other seasons ignore. Also associated with Malvastrum spicatum (Everist sceptical) and Sida spp.

Can be refuge of diagnostically destitute dealing with staggers syndromes on the plains

• Tribulus staggers — hind limb incoordination
• Marshmallow staggers (Malva parviflora) — similar CS to humpy back but no ‘hump’ — usually young sheep — not summer
• Various congenital spinal cord conditions — ataxia (personal experience limited)
• Marginal hypocalcaemia due oxalate plants (eg Portulaca oleracea — Pigweed) — drunken incoordination — different to pre-lambing hypocalcaemia.

Greatest implications are difficulties produces if wish to muster for management procedures (eg Shearing for autumn lambers) during period.

Clinical signs

Clinical signs are the key way of differentiating from the above

• ‘Staggers’ / ataxia are not Clinical Sign (fatigue may produce)
• Portion affected small, from only a couple to five percent of mob
• Is not present when sheep first disturbed — takes an extended period of driving (usually over one kilometre)
• Affected sheep lag behind mob
• Increasingly short and stilted gait — almost walking on the spot
• Then lower head, bring hind legs forward under abdomen and arch back — humpy back
• Then flop down — sometimes with a sigh
• After brief rest (few minutes to twenty minutes) rise again to follow flock. Problem recurs within shorter distance
• Sheep may die if forced to make repeated attempts to walk.

Gross pathology

No gross pathology — perhaps exertional emphysema of lungs. May find Solanum esuriale berries in rumen.

Laboratory Results

Variety of pathology recorded

• Nothing
• Wallerian degeneration of spinal cord white matter — caution?
• Myogeneration hind limb skeletal muscle
• Focal myocardial degeneration and necrosis.

Treatment Options

Affected sheep should be left to rest or transported to shed, yardsetc.- will recover if not already over stressed.

Control / Prevention Options

Awareness of condition so that can avoid driving sheep to deaths — pick up lagging sheep and transport to yards. Shift management procedures from risk time of year — as sporadic from year to year — appropriate?

References

Qld DPI Information Sheet — McLennan and Knights, 2005. http://www.dpi.qld.gov.au/sheep/10034.html

McKenzie, Ross. CD Toxicology for Australian Veterinarians, 2002.