POST-TREATMENT REACTIONS IN CATTLE DURING EXTENSIVE FIELD TESTS OF SYSTEMIC ORGANOPHOSPHATE INSECTICIDES.

Treatment, grub infestation, and post-treatment reaction data is given for 11,537 range-managed beef cattle, of all age classes, treated for grub and louse control with various systemic organophosphate insecticides during the period 1956 to 1964. Two cows died from perforation of the throat during administration of Trolene boluses. Of 6,858 calves, 71 showed adverse reactions with 4 dead. Of 4,679 cattle over one year of age, 3 showed adverse reactions with one death. No typical organophosphate poisoning occurred. One death resulted from a paraplegic reaction and necropsy showed spinal nerve damage of the type often associated with the presence of H. bovis grubs in the spinal canal. Seventy-three reactions, with 4 deaths, were of a bloat-salivation type, and necropsies of 3 indicated anaphylaxis, the other an extensive pharyngeal - esophageal necrosis. Reactions were directly associated with grub abundance. Other stress factors coincident to insecticide treatment, such as Bang's vaccination and dehorning, did not enhance reactions, and incipient coccidiosis did not predispose to reactions, nor did insecticide treatment increase susceptibility to coccidiosis. It is concluded that the observed adverse reactions resulted from the killing of grubs situated in the animal tissues.