Beschreibung:
<jats:p><jats:bold>SYNOPSIS. </jats:bold> In 5 experiments the infectivity and immunogenicity for chickens of sporulated oocysts of <jats:italic>Eimeria acervulina</jats:italic> that had been previously subjected to different levels of gamma radiation was tested. It was found that the irradiation doses can be divided into three groups: a) High dosage levels of over 16,000 rad impair the reproduction of the parasites so that few or no oocysts are discharged and no immunity is produced. b) Low dosage levels of 7,000 rad and less permit reproduction and development of immunity not perceptibly different from that resulting from unirradiated oocysts. c) An intermediate range of levels with the optimum from 9,100–13,700 rad induces attenuation while at the same time assuring sufficient immunogenic response.</jats:p><jats:p>A dose of 100,000 oocysts or more per bird is required to produce immunity. The optimum irradiation dose increases with the immunizing dose. It was concluded that the development of an irradiated vaccine is possible.</jats:p>