Humpy back of sheep. Clinical and pathological observations

Area of Science:

• Veterinary Pathology
• Toxicology
• Sheep Diseases

Background:

• Humpy back disease affects Merino sheep in Queensland, typically appearing in summer after heavy rainfall.
• The condition is suspected to result from the ingestion of a toxic plant during mustering for shearing.
• Clinical signs include a characteristic stilted hind limb gait, head lowering, back arching, and inability to walk.

Purpose of the Study:

• To investigate the histopathological changes associated with humpy back disease in Merino sheep.
• To identify the neurological and muscular lesions present in affected animals.
• To explore potential links between environmental factors and disease manifestation.

Main Methods:

• Histopathological examination of spinal cord and cerebellar tissues from affected sheep.
• Clinical assessment of gait and neurological signs.
• Comparison of lesions in affected and unaffected sheep from the same flocks.

Main Results:

• Wallerian degeneration of white matter was consistently observed throughout the spinal cord, predominantly in ventral and lateral columns.
• Degenerative changes were also noted in the posterior cerebellar peduncles in some cases.
• Milder spinal cord lesions were present in apparently unaffected sheep from affected properties, suggesting subclinical effects or early disease stages.
• Severe myodegeneration of hind limb muscles was observed in three affected sheep, potentially exacerbated by transport stress.

Conclusions:

• Humpy back disease is characterized by significant Wallerian degeneration of the spinal cord white matter.
• The presence of similar lesions in unaffected sheep suggests a potential widespread exposure or susceptibility within affected flocks.
• Further research is needed to identify the specific toxic plant and elucidate the pathogenesis of the disease.