Eimeria oocysts in auxiliary feed trays represent a potential source of infection to young broiler chicks

Outbreaks of avian coccidiosis arise after newly-placed chicks ingest high numbers of Eimeria oocysts present in litter. Preventing coccidiosis depends on reducing the number of Eimeria oocysts ingested to a level that either induces or boosts immunity without causing enteric disease. The purpose of this study was to determine if feces in auxiliary feed trays (AFT) contained Eimeria oocysts and, if so, were these oocysts capable of causing a patent infection. Sampling of feces present in AFT or litter was conducted in a total of 16 houses from 11 different commercial broiler farms during a coccidiosis vaccine program. Without exception, appreciable numbers (∼ 10 3 oocysts/gram) of E. maxima and non- E. maxima ( E. acervulina, E. mitis, E. praecox, E. tenella ) oocysts were found in AFT. Nearly all litter samples (14/16) were positive for E. maxima oocysts, while all litter samples (16/16) were positive for non- E. maxima oocysts. As indicated by ITS1 PCR, E. acervulina, E. mitis, E. praecox , and E. tenella oocysts were generally present in all AFT and litter. Experimental infection of susceptible chickens with Eimeria oocysts recovered from AFT revealed that E. acervulina and E. mitis , but not E. maxima, E. praecox , nor E. tenella oocysts were viable and infectious. This finding is consistent with a shorter patent period and thus more rapid progression to full sporulation of E. acervulina and E. mitis . These results indicate that fecal material in AFT represents a potential source of Eimeria infection in young chicks, and removing the trays within 7 days post-placement may reduce coccidiosis outbreaks.