Abstract
A strain of Eimeria tenella of Japan origin was serially passaged 51 times in chicken embryos. Any obvious changes of reproductivity and lethality to chicken embryos of the passage strain were not observed. Chickens infected with oocysts passaged 41 times in chicken embryos showed less severe cecal lesions and hemorrhage, and higher values of body weight gain, feed intake and lower value of feed requirment, compared with chickens infected with oocysts passaged once in chicken embryos. Less severe lesions were also observed in chickens infected with oocysts passaged 51 times in chicken embryos than those in chickens with oocysts passaged once. It was indicated that pathogenicity of the strain was attenuated after serial passage in chicken embryos.
