Some observations on the biology of five strains of Eimeria necatrix.

Five laboratory strains of Eimeria necatrix were characterised with regard to the size of their oocysts, pathogenicity, reproduction, cross-immunity, ability to grow in embryonated eggs, and electrophoretic variation of enzymes. Three strains were highly pathogenic whilst two caused only few deaths and milder changes to the mean body weight gains of infected chickens. Cross-immunity was incomplete judged by scores of lesions after heterologous challenge, and electrophoretic variation of the enzymes lactate dehydrogenase and isocitrate dehydrogenase from oocysts of the five strains was also found. All the strains completed their life cycle in embryonated eggs but only a few oocysts were recovered.