Sustainable nutritional strategies are essential to boost production to meet rising global demand for poultry meat while reducing production costs and environmental pollution. Reduced crude protein (CP) diets with optimized essential-to-total amino acid (E:T) ratios and dietary fiber supplementation have been investigated as promising approaches to improve broiler health and performance. However, the molecular mechanisms and microbial changes underlying these benefits are less understood. This thesis explores how optimized E:T ratios in reduced CP (RCP) and the inclusion of sugarcane bagasse (SB) in the diet influence molecular, microbial, and physiological responses that promote growth, gut health, and resistance to necrotic enteritis (NE).
Chapter 1 provides a brief overview of CP diets and SB to highlight the significance of this study and its main objectives.
Chapter 2 provides a comprehensive review of the literature on the effects of CP and dietary fiber diets on broiler performance and health. It also highlights the knowledge gaps in how these diets influence transcriptomic responses, gut microbial communities, and overall productivity in broiler chickens.
Chapter 3 examined the performance and liver transcriptome of broilers fed an RCP diet. Broilers on 17% RCP with a 0.64 E:T ratio showed similar weight gain and feed intake but had higher (P < 0.01) protein utilization efficiency compared to 19% CP control birds during the finisher stage (d 19-28). Using RNA-seq to analyze the liver transcriptome profile revealed the upregulation of key differentially expressed genes, especially those involved in PPAR signaling and metabolic pathways. This highlights the birds' ability to exhibit metabolic adaptations to low-protein diets that allow them to perform similarly to those on a normal-protein diet.
Chapter 4 evaluated the impact of E:T RCP diet that optimized the performance and health of NE-challenged birds on d 16 of the grower stage. Under healthy conditions, broilers fed a 0.64 E:T RCP (RCP0.64) diet exhibited similar weight gain and feed intake compared to those on the control diet. The NE challenge significantly (P < 0.05) impaired performance, disrupted microbial composition, and altered gene expression related to nutrient transport, barrier function, and immunity. However, challenged birds on the RCP0.64 diet consumed more feed P < 0.05) compared to the control diet, had higher relative abundance of microbial taxa such as Firmicutes (phylum) and Limosilactobacillus (genus), along with increased expression of immunoglobulins (IgY in the jejunum and IgM in the spleen). Although the RCP0.64 diet did not fully eliminate the adverse effects of NE, it helped to reduce their severity by modulating immune responses and enriching beneficial microbes.
Chapter 5 examined the performance and transcriptomic responses of broilers fed an SBsupplemented diet. At the end of the grower phase (d 11-24), SB supplementation increased weight gain and improved feed conversion ratio compared to the control birds. Jejunal and pancreatic RNA-seq revealed significant upregulation of genes involved in mineral and energy transport (TRPM3, SLC16A4, FFAR4, RBP4A), epithelial integrity (WNT9A, TFF3, AGR2), redox and immune defense (DUOX2, GPX2, MHCY6), and growth regulation (POU1F1) in SB-fed birds. Furthermore, the upregulated genes were enriched for gene ontology biological processes, such as maintenance of gastrointestinal epithelium, gastric acid secretion, sodium ion transport, and response to oxidative stress following SB supplementation. The enrichment of these processes supports the notion that SB supplementation improved nutrient digestibility and absorption, as well as intestinal barrier function for better performance.
Overall, the findings of this thesis demonstrate that optimized 0.64 E:T RCP diet and fiber-rich SB diet are associated with organ-specific transcriptomic profiles and shifts in microbial composition linked to metabolism, nutrient transport, barrier integrity, and immune-related processes. This integrated approach provides a sustainable way to enhance performance and support gut health in modern broiler production.