T h e Effects of Variable Dosages of Spor- ulated Eimeria Acervulina Oocysts on Chickens*

ONE of the most important factors in the development of clinical or fatal coccidiosis in susceptible chickens is the dosage of sporulated oocysts ingested at one time. Since Johnson (1927) drew attention to "the relationship of the num-ber of sporulated oocysts ingested to the severity of the disease, " only very limited information has been available regarding this important factor. Further, Johnson (1931) reported "complete temporary ces-sation of (egg) production " when sus-ceptible birds were inoculated "with large doses of pure cultures " of Eimeria acer-vulina. He did not reveal, however, what was considered as a large dose. Tyzzer (1929) also drew attention to the effect of the size of the dose of E. acervulina, but did not mention what approximate dosages were used. In a comparison with Eimeria tenetta his statement that "while with E. tenella a single feeding of a relatively mod-erate number of oocysts may produce serious or fatal results, many times the number of E. acervulina oocysts may be fed in a single dose without apparent dam-age to the host, " indicated that a clinical dosage for E. acervulina was much higher than for E. tenella. These studies with E. ecervulina were •Published as Technical Paper No. 367 with the approval of the director of the Oregon State Agricultural Experiment Station. Contributio