Narasin is a polyether monocarboxylic
acid antibiotic produced by Streptomyces aureofaciens. An extensive series of battery cage trials was conducted to evaluate the efficacy of
narasin against recent field isolates of the pathogenic species of chicken coccidia. Statistical analyses of the results of these studies revealed that each successive increase in the concentration of
narasin produced a significant reduction in the severity of cecal and intestinal lesions when compared with those in infected nonmedicated controls. Increasing the concentration of
narasin also produced significant improvements in
weight gain and feed efficiency when compared to gain and feed efficiency of infected nonmedicated controls. Maximum
weight gain of birds infected with Eimeria tenella alone was obtained at a
narasin concentration of 60 ppm, but birds infected with E. tenella plus intestinal species of coccidia, when medicated with 80 ppm
narasin had
weight gains significantly greater than those of birds medicated with 60 ppm
narasin.
Weight gain improvement decreased at
narasin concentrations greater than or equal to 100 ppm. Results of these studies confirm the effectiveness of
narasin in controlling coccidial
infections produced by recent field isolates of the pathogenic species of chicken coccidia.