Comparison of anticoccidial efficacy, resistance and tolerance of narasin, monensin and lasalocid in chicken battery trials.

The anticoccidial efficacy, host tolerance, and projected resistance development of the three polyether antibiotics, monensin, narasin, and lasalocid were compared. The efficacy of narasin against different coccidial strains was found to parallel that of monensin in as much as strains which were refractory to monensin were also refractory to narasin. In contrast, lasalocid easily controlled some strains which were not well controlled by either narasin or monensin and failed to control one strain readily controlled by these two antibiotics. In growing chicks, lasalocid at the projected use level of 75 p.p.m. and narasin at an efficacious level of 100 p.p.m. were both better tolerated than monensin at the recommended use level of 121 p.p.m. The frequency of mutants resistant to each of these polyether compounds was found to be less than 8.6 X 10(-9) per drug sensitive oocyst for one strain of Eimeria tenella. This corresponds to less than 0.036 and 0.148 as frequent as mutants of this strain resistant to glycarbylamide or to amquinate, respectively.