CERVICAL AND THORACIC VERTEBRAL MALFORMATION (WEAK NECK) IN COLOMBIA LAMBS

The purpose of this study is to describe a developmental defect of the caudal cervical and cranial thoracic vertebrae in 11 purebred Colombi a lambs. The lambs were either affected at birth, or developed the con dition within the first 18 days of age. Cervicothoracic kyphosis, with a compensatory cervical Iordosis and ataxia were common; 8 lambs had abnormal head posture, characterized by inability to lift the head fro m the ground. One lamb had rigid head and neck, and had to move the en tire body to look to the left or right. Neurological signs included at axia, tetraparesis, diminished conscious proprioception, and increased patellar and triceps reflexes. One lamb had inspiratory strider becau se of compression of the trachea in the area overlying the abnormal ve rtebrae (cervical vertebrae 6 [C6] and 7 [C7]). Radiographic and patho logical abnormalities included malalignment and malarticulation of the caudal cervical and cranial thoracic spine, rounded cranioventral mar gins in the bodies of vertebrae C7 and T1, wedging of the intervertebr al disc spaces between C6 and T1 vertebrae, and hypoplasia of the dens . Pathological changes in the soft tissues included hypoplasia of the cervical epaxial and hypaxial musculature, with associated focal areas of myodegeneration. Mild Wallerian axonal degeneration, compatible wi th a mild cord compression syndrome, was found in 3 lambs in the cervi cothoracic spinal cord adjacent to the vertebral anomalies. The concen trations of copper and selenium in blood, plasma, or tissues were norm al in 10 of 11 lambs. All but one of the lambs in which pedigree infor mation was provided were genetically related. Siblings born as twins t o 5 of the affected lambs were normal, but both lambs from one twin pr egnancy were affected. Owners reported that breeding stock had been sh ared among the ranches. Because of the close familiar relationships of the affected lambs, the condition is suspected to have a hereditary b asis. (C) 1995 by the American College of Veterinary Internal Medicine .