Delayed neurotoxicity caused by chronic feeding of organophosphates requires a high-point of inhibition of neurotoxic esterase.

Experiments are reported showing that chronic feeding of either mono-2-cresyl diphenyl phosphate or diisopropyl phosphorofluoridate (DFP) to hens does not cause clinically observable delayed neurotic effects prior to a point when inhibition of neurotoxic esterase (NTE) of brain and spinal cord reaches 70-90%. These results are contrary to another study with diisopropyl phosphorofluoridate, which claims neuropathy without high inhibition, but are supported by results of chronic feeding experiments with tri-o-cresyl phosphate. The discrepancy cannot be attributed to differences in the strains of hens used.