Spontaneous lower motor neuron disease with neurofibrillary accumulation in young pigs.

A spontaneous neurologic disease occurred in six 5 weeks old Yorkshire pigs of both sexes from four litters sired by one boar. Clinically, the disease was characterized initially by bilateral posterior ataxia and weakness which rapidly progressed to tetraplegia by 10 weeks of age. By light microscopy, there was bilateral neuronal chromatolysis, degeneration and loss restricted to motor nuclei in the ventral horns of the spinal cord, in the medulla oblongata and midbrain. In addition to diffuse Wallerian-type degeneration in the spinal cord white matter and ventral peripheral nerve roots, there was prominent neurogenic atrophy of skeletal muscle. Ultrastructurally, the perikaryon and processes of affected neurons contained massive accumulations of single 10 nm diameter neurofilaments. Copper concentrations of both the commercially prepared ration and the livers were within normal limits.