Eimeria maxima: a comparison of two laboratory strains with a fresh isolate

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Abstract
Oocysts of the Weybridge and Houghton strains of E. maxima and a fresh field isolate were similar and measured on average 30.9 .times. 22.4 .mu.m. The Weybridge strain and the field isolate produced similar pathogenic effects in 6 wk old chickens, high doses causing 50-80% mortality and severe weight loss. The Houghton strain was slightly less pathogenic and few birds died, but more oocysts were produced. With each strain, a single dose gave complete immunity to a light challenge with the homologous strain. Two or 3 immunizing doses gave complete immunity to a heavy homologous challenge but were not sufficient to protect against heterologous challenge.