Coccidiosis is one of the most prevalent intestinal diseases caused by protozoan parasites of the genus Eimeria in poultry. The main objective of this work was to investigate the interrelationships of dietary strategies, Eimeria infection, and intestinal health of broiler chickens. A series of six studies was conducted in the dissertation. In the first study, growth performance, and dynamic change of intestinal integrity were evaluated in broiler chickens challenged with graded doses of mixed Eimeria spp. The higher Eimeria doses birds received, the more severe intestine damage was observed in several gastrointestinal health parameters, including intestinal morphology, nutrient digestibility, and intestinal lesion scores. Moreover, significant linear increases of intestinal permeability were observed on 5, 6, and 7 days post-infection with increasing infection doses. In the second study, the effects of increasing the challenge of E. maxima on growth performance and gene expression of tight junction proteins and nutrient transporters were investigated in chickens. The results demonstrated that E. maxima infection reduced growth performance and regulated gene expression of nutrient transporters and tight junction proteins in a dose-dependent manner. In the third experiment, the endogenous loss, apparent ileal digestibility, and standard ileal digestibility of amino acids were studied to reveal the actual capacity for nutrients absorption in Eimeria-infected birds. Increasing infection severity of E. maxima linearly increased endogenous loss of amino acids and reduced the apparent and standard ileal digestibility. In the fourth and fifth experiments, the effects of nitrocompounds on inhibition of Eimeria development in the host were tested in vitro and in vivo. The 2-nitro-1-propanol was not able to maintain efficient growth performance, but it improved nutrient digestibility and inhibited Eimeria infection. Lastly, the sixth study investigated the supplementation of specific amino acids in low-crude protein diets in broiler chickens challenged with Eimeria. Adding 0.75% of supplemental arginine, glutamine, or threonine in low crude protein diets improved the intestinal health of birds, but methionine supplementation exacerbated the intestinal damage along with coccidiosis.
