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Abstract
CASE HISTORY: In 2008, six lambs within a flock of Dorpercross sheep were born with musculoskeletal and neurological disease. Clinical signs included hindlimb weakness, and urinary incontinence.
CLINICAL FINDINGS: All lambs had focal, inverted areas of alopecic skin over the caudal sacrum, and short, often kinked tails. Four affected lambs were subject to euthanasia, and necropsied. On gross examination, the arches of sacral vertebrae were absent, and spinal nerves and meninges were adherent to the overlying subcutis. Other gross lesions included narrow, elongated skulls, herniation of the occipital lobes into the caudal fossas, hydrocephalus, and syringomyelia. One lamb had coning of the cerebellar vermis, but cerebellar herniation through the foramen magnum was not identified.
DIAGNOSIS: Spina bifida, with associated malformations of the central nervous system.
CLINICAL RELEVANCE: Examination of breeding records suggested either an autosomal recessive or partially penetrant autosomal dominant pattern of inheritance. Because of the associated tail lesions it is proposed that the pathogenesis of this syndrome involves a defect in development of the tail bud (secondary neurulation), that tethering of the spinal cord resulted in the clinical signs, and abnormal pressure of the cerebral spinal fluid resulted in the defects in the skull and brain.
Acknowledgements
The authors wish to acknowledge the cooperation of the owners of the sheep farm involved (who wish to remain anonymous), and Dr Moira Brennan, who contributed substantially to the gross and histological evaluation of these cases. KA Potter also wishes to thank Washington State University, Pullman WA, USA, for sponsoring her sabbatical, and the Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand, for hosting that sabbatical.