Anticoccidial efficacy of narasin in battery cage trials

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.