Cerebellar abiotrophy and segmental axonopathy: two syndromes of progressive ataxia of Merino sheep.

Findings of a study of 39 sheep with progressive ataxia from 14 farms in the Yass district of New South Wales are described. Microscopic lesions in 25 sheep, 3.5 to 6 years of age, diagnosed as having clinical cerebellar disease, consisted of an apparent primary loss of cerebellar Purkinje neurons, and glial cell accumulation. It is suggested that this previously unreported disorder may be an hereditary cerebellar abiotrophy of Merino sheep. A further 14 sheep, 1 to 4 years of age, had distinguishable clinical signs referable to a spinal cord lesion with widespread segmental axonal ballooning, or "spheroids", in the white matter of the brain and spinal cord. It is suggested that these sheep have a unique form of neuroaxonal dystrophy, described here as segmental axonopathy, and that this is likely to be the same condition described previously as Murrurindi disease (Hartley and Loomis 1981).