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.

A series of four floor pen trials was conducted to evaluate the effects of narasin and roxarsone, both alone and in combination, on their capacity to control severe Eimeria tenella infections in broilers. Three levels of narasin (0, 60, and 80 ppm) were fed to chickens receiving either 0, 25, or 50 ppm roxarsone in a factorial design. Cecal coccidiosis was induced by seeding the litter with ionophore-tolerant and ionophore-sensitive strains of E. tenella. After 8 days, 10 birds/pen were killed and their cecal lesions scored. Performance (body weight and feed consumption) and mortality were measured at the termination of the trials. Narasin reduced the severity of cecal coccidiosis as measured by a reduction in cecal lesions and an improvement in bird performance. Roxarsone also reduced cecal lesion scores. The highest level of roxarsone (50 ppm) in combination with 60 or 80 ppm narasin produced additive responses in the control of E. tenella infections. Maximum performance was obtained when narasin alone was fed at 80 ppm; drug combinations improved performance when compared with that of nontreated or roxarsone only-medicated groups.

Narasin is effective against all species of chicken coccidia when tested in battery cage and floor pen studies. To confirm the efficacy of narasin under practical broiler production conditions, the drug was fed at concentrations of 60 ppm or 80 ppm to broiler chickens being raised by six different commercial broiler producers in five different geographic areas. Monensin was fed in each trial at a concentration of 100 ppm or 121 ppm as a reference control. The usual management practices of each of the integrated broiler companies were followed throughout the respective trials. Nine trials were conducted and approximately 100,000 broilers were tested for each treatment. No adverse reactions attributable to treatments were observed in any of the trials, and performance results obtained with narasin-medicated birds were generally comparable with those obtained with monensin-medicated birds in the same trial. These findings support the conclusion that narasin at final feed concentrations in the range of 60 to 80 ppm can be safely and effectively used as an anticoccidial agent in commercial broiler production facilities.