This experiment aimed to evaluate the effects of probiotic administration route (PAR), dietary nutrient density (DND) and Eimeria challenge (ECH) on performance, gut morphology, and hematological variables in broiler chickens. Eggs carrying 17.5-day-old broiler embryos were injected with 0.1 ml distilled water (vehicle control) or 0.1 ml distilled water containing probiotic. A group of 72 intact eggs was also included in the experimental design used asrepresenting un-injected control. Hatchlings from intact and probiotic injected eggs were further evaluated in a 42-d floor-pen trial along with 465 additional hatchmate chicks. Chicks were placed in two environmentally controlled houses, each having 30 floor pens randomly assigned to the following six treatments: conventional chicks receiving a standard diet with (group 1) or without (group 2) probiotic; conventional chicks receiving a 5% diluted diet with (group 3) or without (group 4) probiotic; and in ovo probiotic-administered chicks receiving standard diet (group 5) or 5 % diluted diet (group 6). All birds in one of the houses were inoculated with a pathogenic dose of an attenuated live Eimeria vaccine at 28 d. Chicks receiving in ovo probiotic showed reductions in hatch weight and yolk sac weight compared to control (p<0.05); the same group, however, had a significantly higher weight gain (WG) during the first 10 days post-hatch but this improvement disappeared with age. Groups receiving standard diet exhibited better growth performance than those fed the 5% diluted diet. Eimeria challenge caused significant adverse effects on performance traits, intestinal morphology, and hematological variables. It is concluded that neither PAR nor DND could alleviate Eimeria-induced deteriorations in productivity and health of broiler chickens.

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