Investigations on the Effects of Rearing Space Allowance and Functional Feed Ingre-dients on Pullet Growth and Cecal Digesta Microbiota Attributes Through to the Laying Phase

Poultry rearing environment and diet plays important roles in influencing growth, organ development, immunocompe-tency, gut microbiota composition, and antimicrobial resistance (AMR). This thesis evaluated the effect of early-life dietary sup-plementation with yeast bioactive (YB) or co-extruded full-fat flaxseed, a source of omega-3 fatty acids (N-3 FA), under different space allowance (SA) on growth performance, organ development, cecal bacterial composition, short-chain fatty acid (SCFA), lung immune responses, and AMR in E. coli from Lohmann LSL Lite birds. A total of 2,832 day-old pullets were reared in en-riched cages under high (HSA, 348 cm2/bird) or low (LSA, 284 cm2/bird conditions and fed a control (C), C + 3% N-3 FA, or C + 0.05% YB diet from placement to 16 weeks of age (woa) and transitioned to a standard layer diet until 72 woa. Study 1 examined growth performance and cecal microbiota composition. Dietary N-3 FA or YB supplementation and SA did not affect organ de-velopment, except for reduced small intestine weight at 4 woa. By 16 woa E. coli counts were lowest in LSA pullets, and both N-3 FA and YB diets reduced the counts compared with the control-fed birds. Beta-diversity analyses revealed distinct bacterial com-munity structure, with enrichment for Bacteroides fragilis in LSA birds fed N-3 FA or YB at 4 woa. Study 2 investigated SCFA profiles and cecal bacterial association. LSA pullets showed higher propionic and isobutyric acid at 4 and 16 woa, N-3 FA-fed birds had the highest n-butyrate levels, while control had the lowest. Correlation analyses linked Barnesiellaceae and Lactobacil-laceae with n-valeric and acetic acids in N-3 FA-fed birds, indicating diet-dependent microbial metabolic shifts. Lung expression of IL1b, IL2, and IL8 genes varied across diets and SA, suggesting systemic immune modulation. Study 3 explored AMR dynam-ics. Among 428 E. coli isolates, 35.7% were resistant to at least one antimicrobial, with resistance decreasing with age. Whole-genome sequencing of 252 pure E. coli isolates identified 19 antibiotic resistances genes (ARG) and 29 plasmids influenced by diet, SA, and age, with phylogroups A and B1 predominating. Overall, early dietary supplementation with N-3 FA or YB under different SA modulated gut microbiota and SCFA profile and immune while influencing AMR in E. coli, supporting sustainable poultry production.
Date: Friday January 9, 2026 at 9:00am