The infectivity ofEimeriasporozoites recovered from Monensin medicated chickens1

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Abstract
Sporozoites of embryo‐adapted lines olEimeria tenella, E. brunetti and E. necatrix were recovered from monensin medicated chickens. The viability of these sporozoites was compared with that of sporozoites recovered from unmedicated birds by assessing their infectivity in chicken embryos. Sporozoites of the three species of Eimeria recovered from 100 parts/106 monensin‐medicated birds produced infections in embryos which were 94 to 98% less severe than infections resulting from the inoculation of sporozoites recovered from unmedicated chickens. A concomitant scanning electron microscope study revealed no apparent ultrastructural damage to the exposed sporozoites. Timed medication experiments in chickens showed that medication with monensin for the period covering sporozoite penetration in vivo was almost completely effective, being comparable to continuous medication. Medication started before infection (to ensure tissue concentrations of monensin) but terminating 5 to 7 hours before the oocysts were inoculated was ineffective.