Localized diseases of the bovine brain and spinal cord.

Localized lesions of the central nervous system do occur in cattle. Those affecting the cranial nerves and focal lesions of the spinal cord are most easily recognized by careful neurologic examination. Once the lesion has been anatomically localized, likely etiologic causes can be pursued. Probably the most common cause of cranial nerve deficits in cattle is listeriosis. Important differential diagnoses include brain and pituitary abscesses and extensions of ear infections. Other possible causes include PEM, TEME, hypovitaminosis A, and several rare, sporadic causes. In young cattle, spinal trauma and vertebral body abscesses are the most common causes of progressive paresis resulting from spinal cord lesions. Congenital abnormalities must be considered in the differential diagnoses for very young calves. Non-neurologic conditions, including fractures of the limbs and especially nutritional muscular dystrophy, must be ruled out. In older cattle, compressive neoplasms, most notably lymphosarcoma, are primarily responsible for progressive paresis. Differential diagnosis should include other neurologic conditions such as delayed organophosphate neurotoxicity; early progressive diffuse neurologic diseases such as rabies, pseudorabies, and botulism; plant toxicities; and non-neurologic conditions resulting in recumbency, such as hypocalcemia and musculoskeletal trauma.