Activity of Levamisole (l Form of Tetramisole) in Control of Nematode Parasites and Body Weight Gains of Feedlot Cattle

Abstract

SUMMARY Efficacy of levamisole ( l form of tetramisole) in the control of gastrointestinal parasites and effect of the drug on body weight gains were determined in steers in a commercial feedlot. In experiment I, steers were in drylot for 120 days. In the 2nd experiment, steers had been kept in winter temporary pasture for 91 days before they were put in drylot for a 64-day fattening period. In both experiments, the steers given (by drench) levamisole (8 mg./kg. of body weight) had average daily body weight gains of 0.1 kg. after 66 days and after 91 days, respectively, after medication was given. Comparable body weight gains, however, were made by the nonmedicated groups of steers during the later part of experiment II. The 2nd medication given at the end of the 1st period of the 2nd experiment did not improve the rate of gain of the steers. The average number of nematode eggs passed by steers in experiment I was significantly reduced after medication was given. However, a reduction in eggs per gram of feces (e.p.g.) count also occurred in the control steers. There was no difference in the average numbers of gastrointestinal nematodes recovered at necropsy from the treated and control steers at the end of experiment I. Midway through experiment II, medication had significantly reduced the average fecal egg counts. Also, egg counts from the control steers had significantly decreased at the end of experiment II. In experiment III, feedlot steers were given a single treatment of a pelleted formulation of levamisole topdressed on a feed supplement at the dose level of 8 mg./kg. of total body weight of feedlot steers. The medication was 94 to 99% efficacious against adult forms, and 68 to 81% efficacious against larval forms, of the nematode parasites enzootic in the area. The formulation was easily administered to the steers and was readily eaten by most of them. Medicated steers did not have signs of intoxication.