Eimeria tenella in gnotobiotic chickens: hematocrit, weight change, cecal pathology, and mortality.

On days 5 to 8 after oral inoculation with 200,000 Eimeria tenella oocysts, the mean hematocrits of bacteria-free, Bacillus cereus-monoflora and conventional chickens were equally reduced below control values. Weight loss was first observed in bacteria-free and monoflora fowl between days 4 and 5 after E. tenella inoculation, whereas conventional fowl initially displayed weight loss between days 3 and 4. Gross cecal lesion scores and total mortality of 4 experiments were not significantly different for the 2 gnotobiotic (bacteria-free and monoflora) groups, but these values for both groups were significantly less than those of infected conventional control animals. Since hematocrits were equally depressed in gnotobiotic and conventional animals, and survival was significantly greater in the former, it is suggested that factors in addition to blood loss cause mortality during E. tenella infections. The correlations between the severity of cecal lesions and per cent mortality suggests that these phenomena may be closely related. The present experiments with gnotobiotic fowl indicate that the normal flora is involved in the cecal pathology and mortality caused by cecal coccidiosis in conventional animals.