Tetrachlorvinphos as an ineffective feed additive in control of gastrointestinal nematodes of beef cattle.

Tetrachlorvinphos was evaluated for anthelmintic efficacy as a feed additive against gastrointestinal nematodes of cattle. Tetrachlorvinphos was added to the mineral mixture of medicated cattle (n = 13) at the rate of 1.6 mg/day/kg of body weight for a 29-week period beginning May 2, 1975. Data suggest that the level of parasitism, as estimated by the number of nematode eggs per gram of feces, was not reduced by the addition of tetrachlorvinphos to the mineral mixture of medicated cattle. Results obtained from identification and quantification of nematodes recovered at necropsy from 6 medicated and 6 nonmedicated control heifers indicated that tetrachlorvinphos was ineffective as an anthelmintic against gastrointestinal nematodes of cattle.