Sporulated oocysts of Eimeria lettyae were administered orally to 5-day-old or 18-day-old northern bobwhites (Colinus virginianus, L.). Five-day-old bobwhites were more susceptible based on higher mortality and reduced weight gain. A dose of 5 × 105 oocysts produced 25–43% mortality in 5-day-old bobwhites, but none in 18-day-old bobwhites. A dose of 1 × 106 oocysts/bobwhite produced 83–100% mortality in 5-day-old bobwhites, and 17–83% mortality in 18-day-old bobwhites. Body weight gain was reduced significantly with a dose of 1 × 105 oocysts or greater in 5-day-old bobwhites and with a dose of 5 × 105 oocysts or greater in 18-day-old bobwhites. Infection in all age groups reduced concentrations of plasma pigment and plasma protein, but did not affect packed cell volumes. No grossly visible lesions were present in the intestine although there was a shortening of the villi in the duodenum. In mature bobwhites, infection with E. lettyae did not cause mortality, but did reduce egg production and fertility.
