Occipital condylar dysplasia in two Jacob sheep.

Two young Jacob sheep which presented with severe ataxia and torticollis had abnormally formed atlanto-occipital joints. Postmortem examination revealed marked dissimilarity in size between the left and right occipital condyles, with reduction in size of the foramen magnum. The atlantoaxial joint and dens were normally formed, and were not abnormally positioned in radiographs taken of one lamb. Histological evaluation of the cervicomedullary junction demonstrated extensive loss of axons and myelin, gliosis, and mild hydromyelia in one lamb.