Critical neurohistopathologic evaluation of clinically healthy commercial single-comb White Leghorn hens.

A neurohistopathologic study was conducted to determine the types and incidence of spontaneous lesions of the nervous system in healthy adult hens. Tissues examined were brain, three levels of spinal cord, and sciatic nerves from 92 healthy commercial hens from a single commercial egg-production flock judged above average in health. These hens represented negative controls (untreated or given corn oil) in 9 separate toxicologic studies. Minimal to mild focal proliferative or degenerative microscopic changes were detected at all levels of the nervous system. More than 50% of the hens had lymphocytic perivascular cuffing and focal gliosis in the central nervous system. Similarly, lymphocytic foci (in nerve sheaths or within fasciculi) and Schwann cell hyperplasia were commonly seen in sciatic nerves. The spinal cord exhibited neuronal swelling and chromatolysis frequently; axonal degeneration (in brain and spinal cord) and swelling or degeneration of nerve fibers in sciatic nerves were observed sporadically. Most changes were rare or mild. A few chickens had mild or moderately severe perivascular cuffing and focal gliosis. The significance of these findings is discussed in relation to the use of the adult hen in neurotoxicologic evaluations.