The Effect of Age on The Susceptibility to Tri-Ortho-Cresyl Phosphate Induced Delayed Neurotoxicity in Two Different Breeds of Chickens

The reason for the insusceptibility of young animals to organophosphorus-induced delayed neurotoxicity (OPIDN) remains to be elucidated. The present study was undertaken to determine the influence of age-related changes in hormone concentration on the development of OPIDN in domestic chickens. Growth hormone and testosterone radio immunoassay were utilized to estimate levels of both hormones in this study. It was demonstrated that a relatively fast growing broiler-breed of chicken developed OPIDN when dosed with a single oral dose (500 mg/kg body weight of tri-ortho-cresyl phosphate (TOCP) at six weeks of age while a slower growing layer-breed was not susceptible until 12 weeks of age. The serum growth hormone and testosterone profiles indicated that the growth hormone concentration began to decline in both breeds approximately three weeks before they became susceptible to OPIDN and that testosterone concentrations in the broiler breed increased significantly from one to nine weeks of age; while testosterone concentrations in the layer-breed birds remained relatively constant. TOCP had no significant effect on serum growth hormone in immature chickens.