Pastures were topdressed with pellets of 5 fensulfothion at the rate of 2 lb active ingredient (a.i.) /acre, and groups of four sheep were grazed on the pastures after withholding periods of 0, 11, 2V, 29, and 40 days. Sheep in the O-day group developed symptoms of organophosphate poisoning after 4 days grazing, and their erythrocyte cholinesterase activity was reduced by 80. None of these sheep died and their subsequent recovery was rapid. In the other groups none of the sheep developed any symptoms of poisoning, and the depression of their erythrocyte cholinesterase activity was progressively less as the length of the withholding periods increased. No fensulfothion was found in fat of sheep in the O-day group.
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