Efficacy of narasin in the prevention of necrotic enteritis in broiler chickens

The efficacy of narasin in the control of necrotic enteritis (NE) was inves tigated in a floor pen study of 2000 broiler chickens using a Clostridium p erfringens feed inoculum challenge model. Treatments were 1) nonmedicated, nonchallenged; 2) nonmedicated, challenged; 3) narasin, nonchallenged; 4) n arasin, challenged. Narasin was administered at 70 ppm in the feed from day 0 to trial termination on day 41. Challenge inoculum contained approximate ly 1 x 10(8) colony-forming units CP/ml and was administered from day 14 to day 16. In the unmedicated groups, challenged birds had significantly (P < 0.05) lo wer mean body weight and reduced feed efficiency at day 21 and significantl y (P < 0.01) higher cumulative NE mortality at day 41 compared with unchall enged. Similarly, among unmedicated birds, those challenged had a significa ntly (P < 0.01) higher mean NE score on day 17 and significantly (P < 0.05) higher mean huddling scores on days 15-17 than unchallenged. Among challenged birds, those fed narasin had significantly (P < 0.05) high er mean body weight and improved feed efficiency at days 21 and 41 and sign ificantly (P < 0.01) lower cumulative NE mortality at day 41 than unmedicat ed. Similarly, among challenged birds, those receiving narasin had a lower mean NE score on day 17 (P > 0.05) and significantly (P < 0.05) lower huddl ing scores on days 16 and 17 than unmedicated. Coccidiosis lesion scores we re zero for birds euthanatized from all treatment groups on day 17, suggest ing that the beneficial effects of narasin were not due to prevention of co ccidiosis. This study thus provides evidence that narasin is effective in t he prevention of necrotic enteritis in broiler chickens.