Shaping the optimal poultry gastrointestinal tract microbiome through dietary interventions to aid in achieving net zero emissions and sustainable poultry production systems

Abstract

Achieving net-zero emissions in global poultry production requires strategies that improve efficiency while reducing environmental impact and maintaining bird health. Central to this is the gastrointestinal tract (GIT) microbiome, which plays a key role in nutrient utilisation, immune function, and productivity. This thesis explores how dietary interventions can be used to shape a favourable broiler microbiome, supporting bolt, performance and sustainability. A major challenge Is reducing reliance on soybean meal, the primary protein source in broilerr diets. Although nutritionally optimal, soybean production is linked to deforestation and high land use change (LUC) emissions. Identifying viable altematives therefore requires evaluation not only of nutritional value and digestibility, but also impacts on bird health, welfare, microblome development, scalability, and environmental footprint.

Chapter 1 reviews conventional (e.g. oilseed rape, DOGS) and non-conventional protein sources (e.g processed animal proteins, insects, algae, and single-cell proteins), highlighting variability in performance and emphasising the microbiome's role in determining nutritional value.

Chapter 2 assesses fifteen alfematlve proteins using in vitro digestibility, identifying black soldier fly, chlorella, splrulina, porcine processed animal prolain (PPAP), and single-cell protein (SCP) as promising candidates, with PPAP, SCP, and chlorella showing the greatest potential.

Chapter 3 evaluates PPAP in vivo, demonstrating that inclusion at 5-10% does not negatively affect performance, health, welfare, or microblome maturation compared to soybean-based diets, while inducing adaptive microbial metabolic shifts.

Chapter 4 compares all five candidates, integrating performanoe, welfare, microbiorne, and life cycle carbon footprint analysis. SCP and PPAP emerge as the most balanced options, combining good performance with lower emlssions.

Overall, this thesis shows that alternative proteins can reduce reliance on soy, but highlights the importance of contextual factors such as cost, scalability, and regulation. It also demonstrates that soybean LUC strongly influences comparative carbon footprints, and that using low-LUC soybean reduces the apparent advantage of alternatives . As production technologies improve, these novel proteins are likely to play an increasingly important role n sustainable poultry systems.

Thesis is embargoed until 31 July 2031.

Date of Award	Jul 2026
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Sharon Huws (Supervisor) & Chris Creevey (Supervisor)