Selection and Characteristics of a Precocious Strain of E.tenella

To find differences of characteristics between precocious and parent strains of E.tenella,26 passages were selected by serial through chickens using the method as described by Jeffers.The differences between the two strains were analysised according to the sizes of sporulated oocysts,reproduction and pathogenicity.The prepatent period of precocious strain was 118 h compared with 141 h of parent strain.The size of sporulated oocysts of precocious strain was remarkably smaller than that of the parent strain(P0.05),and reproductive potential was correspondent with that of parent strain(P0.05).In the pathogenicity assay,average weight gains of 4 different doses of the precocious strain were not significant difference compared with the control group(P0.05),whereas average weight gains of the parent strain were decreased markedly than control group(P0.05 or P0.01).The mortality of 4 different doses of the precocious strain was zero,whereas that of the parent strain was 0,25%,25%,31.3% respectively,More dose infected,there were more differences in lesion score between the precocious and parent strain.These results showed that the precocious strain of E.tenella possessed shorter prepatent period and less pathogenicity than parent strain and its reproductive potential was corresponding with parent strain.