Narasin is effective against all species of chicken coccidia when tested in short-term battery cage experiments. The efficacy of
narasin at concentrations of 20, 40, 60, 80, and 100 ppm was evaluated in ten floor pen trials in which commercial broiler production conditions were simulated. To provide intentional exposure to different levels of coccidia challenge, the litter of some pens was seeded with oocysts of each of the pathogenic species of chicken coccidia, whereas some pens were left nonseeded.
Weight gain, feed efficiency, and lesion score data from the ten trials were analyzed as one randomized block experiment. Medication with
narasin resulted in a significant reduction in lesion scores and significant improvement in
weight gain and feed:gain ratios when compared with scores and gain of nonmedicated controls for both seeded and nonseeded pens. Each increase in
narasin concentration up to 100 ppm for the seeded pens and up to 80 ppm for the nonseeded pens resulted in a significant reduction in cecal lesion scores. Although maximum
weight gain in the seeded pens was obtained with 40 ppm
narasin, concentrations greater than or equal to 60 ppm
narasin were significantly better than the 40 ppm concentration in improving feed:gain ratios. These results confirm the effectiveness of
narasin in controlling
coccidiosis in broilers exposed to oocysts in the litter of floor pens. Furthermore, a clear relationship between the response to
narasin and the level of oocyst challenge was demonstrated.