Effects of increasing oocysts doses of mixed E. maxima, E. acervulina, and E. tenella on lesion scores in the upper intestine, middle intestine, and ceca of broiler chicken (6 DPI). Average scores of each treatment are present at the top of the bar. a, b Treatments with different letters are significantly different (P < 0.05). (A) Upper-intestine; (B) middle-intestine; (C) ceca. The study evaluated the effects of graded challenge of Eimeria spp. on growth performance and gastrointestinal health of broiler chickens. Birds were challenged with E. spp. on day 13. (Con, Control; Low, the low challenge dose, 6,250 oocysts of E. maxima, 6,250 oocysts of E. tenella, and 31,250 oocysts of E. acervulina; Med-low, the medium-low challenge dose, 12,500 oocysts of E. maxima, 12,500 oocysts of E. tenella, and 62,500 oocysts of E. acervulina; Med-high, the medium-high challenge dose, 25,000 oocysts of E. maxima, 25,000 oocysts of E. tenella, and 125,000 oocysts of E. acervulina; High, the high challenge dose, 50,000 oocysts of E. maxima, 50,000 oocysts of E. tenella, and 250,000 oocysts of E. acervulina). Abbreviation: DPI, day postinfection.