Effect of selenium and vitamin E on the development of immunity to coccidiosis in chickens.

Six experiments were conducted using broiler chickens to study the effect of selenium (Se) or vitamin E supplementation of a corn-soybean meal diet on the immune response to coccidiosis. Immunized chickens fed diets supplemented with .25 ppm Se or 100 IU vitamin E/kg of diet had increased body weight gain and feed intake and a tendency for lower feed conversion ratio than chickens fed unsupplemented diet after a challenge with 150,000 oocysts of Eimeria tenella. In two experiments, chickens fed .25 and .50 ppm of Se and immunized against E. tenella had higher body weight gain and a tendency for higher feed intake and lower feed conversion ratio than unsupplemented chickens when challenged with 150,000 oocysts of E. tenella. Except for a reduction on cecal lesion scores and blood packed cell volume in Experiments 1 and 4, respectively, no dietary effect was observed on cecal lesion score or blood packed cell volume of immunized chickens. Dietary supplementation with selenium or vitamin E reduced mortality and increased body weight gain of nonimmunized chickens infected with E. tenella in three of four experiments. These studies suggest that immunization of chickens against coccidiosis is enhanced by Se or vitamin E supplementation.