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

Authors: Jenkins, Mark; Parker, Carolyn; Yeager, Christina

Submitted to: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2025
Publication Date: 11/28/2025
Citation: Jenkins, M.C., Parker, C.C., Yeager, C.L. 2025. Eimeria oocysts in auxiliary feed trays represent a potential source of infection to young broiler chicks. Journal of Applied Poultry Research. 35(1). Article e100645. https://doi.org/10.1016/j.japr.2025.100645.
DOI: https://doi.org/10.1016/j.japr.2025.100645

Interpretive Summary: Avian coccidiosis is an intestinal disease of broiler and layer chickens caused by protozoan parasites in the genus Eimeria. For years the disease has been controlled by medication of poultry feed with drugs or by administration of vaccines composed of a low dose mixture of Eimeria oocysts. The inefficiency and non-uniformity of vaccination leads to some chicks ingesting too much vaccine and others not getting enough. The former excrete high numbers of Eimeria oocysts, while the latter remain fully susceptible to infection. This is a problem because it situates immunologically naïve chicks proximate to others shedding many infectious oocysts. In our research on the epidemiology of avian coccidiosis, we regularly observe fecal material in auxiliary feed trays that are set out by broiler growers to stimulate eating of feed by young chicks. In this study, we found that the fecal material in these auxiliary feed trays contained high numbers of Eimeria oocysts, some of which were infectious. This observation is useful to poultry companies and growers because it points to the need to remove auxiliary feed trays by 7 days after chicks are placed in a poultry house. This research will benefit the poultry industry by reducing outbreaks of avian coccidiosis by reducing exposure of young chicks to the protozoan parasite.

Technical Abstract: 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 (~ 103 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.