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Abstract
This study explores various strategies for enhancing health, promoting growth, and mitigating environmental impacts by manipulating protein content and amino acids in the diets of broiler chickens infected with Eimeria spp. The dissertation comprises five experiments. The first study investigates the impact of increasing levels of canola meal (CM) or corn distillers dried grains with solubles (cDDGS) relative to soybean meal (SBM) in low-protein broiler diets on growth performance, carcass yield, whole-body composition, and litter characteristics. Results indicate that dietary replacement of SBM with 50g/kg CM or cDDGS yields growth responses similar to standard diets, accompanied by reduced ammonia content due to decreased protein levels. The second study delves into the effects of substituting SBM with CM or cDDGS on amino acid (AA) digestibility, AA transporters, and digestive organ development, aiming to elucidate effects observed in growth performance and ammonia reduction from the first study. Findings suggest that partial replacement of SBM with alternative protein feedstuffs (cDDGS or CM) in low-crude protein (CP) diets minimally affects AA digestibility and mRNA levels of peptides and AA transporters. The third study focuses on evaluating the impact of dietary supplementation with arginine (Arg) and branched-chain amino acids (BCAA) on broilers receiving low-protein diets while infected with mixed Eimeria species. Results reveal that mixed Eimeria infection negatively affects performance, particularly nutrient utilization and genes related to protein synthesis. Supplemental Arg and BCAA exhibited variable effects on growth performance, AA digestibility, and genes associated with protein synthesis and degradation, with Arg consistently promoting weight gain regardless of the Eimeria challenge. In the fourth experiment, the aim is to compare the proteinogenic value of increasing digestible lysine (Lys) or BCAA levels in broiler diets in terms of growth, feeding, and nutrient utilization responses. Higher digestible levels of Lys or BCAA demonstrate similar responses, indicating comparable proteinogenic values between the two amino acids. Lastly, the fifth experiment examines the effect of increasing digestible BCAA with a proportionate decrease in digestible Lys on growth, feeding, and nutrient utilization responses of broilers fed reduced-protein diets. Results indicate a decrease in responses with elevated BCAA and a proportionate decrease in Lys, suggesting that BCAA cannot partially replace Lys under reduced-protein diets.