Toxicology studies conducted in laboratory animals and cattle with coumaphos flowable formulation

A new flowable formulation containing coumaphous, an organophosphate compound, will be used as an insecticide on cattle. It was evaluated for human and cattle safety. The oral LD50 for female rats was 37 mg of formulation/kg and the dermal LD50 for male rabbits was 500 mg/kg. The inhalation LC50 in female rats was 303 micrograms/L. Dermal sensitization in guinea pigs or eye irritation in rabbits were not observed. The formulation was a mild dermal irritant on rabbits, but the erythema reversed itself within 7 days. Spray safety evaluations in cattle included a single application, 2 treatments at 14 day interval, and 2 treatments at 28-day intervals with both 0.5 (highest label rate) and 2.5% (5X) concentrations. Dip vat treatments of cattle included 2 applications at a 7-day interval in 0.3% (highest label rate) and single applications with 0.6% (2X) and 1.2% (4X) concentrations. The cattle did not show significant clinical signs of toxicity nor did trends develop in clinical pathology. The lowest whole blood cholinesterase mean value for cattle sprayed once with a 0.5% concentration was 80% of the pretreatment value at 14 days post-treatment. The cattle receiving 2 dip vat treatments of a 0.3% concentration at a 7 day interval had their lowest cholinesterase reading (53% of pretreatment value) 10 days after the second treatment. Cholinesterase depression in cattle receiving higher than use rate treatment was related to the concentration applied.