The interplay among finishing pig nutrition, gut microbiota and the generation of volatile compounds and greenhouse gases

Abstract

The pork production industry has reached an environmental crisis point, odour and ammonia emissions from pig farms are halting expansion. With pork the second most consumed meat globally, a solution to the demand for cheap and sustainable meat sources must be found.

Chapter 2 will investigate dietary manipulation to mitigate these environmental concerns, while Chapters 3 and 4 will focus on odour producing gut microbiota.

Dietary trials revealed lowering dietary CP by 10g/kg led to a 10% reduction in ammonia emissions on average while decreasing water usage and odour output. A statistically significant positive correlation was observed between odour and ammonia emission, suggesting ammonia reducing diets may prove the greatest hope in reducing overall odour output.

Chapter 3 investigated Clostridioides difficile isolates from piglet faecal samples. One fifth of samples yielded positive results, and isolates were trimethoprim resistant. One isolate belonged to ST11 and possessed all four toxin genes and the other belonged to ST8 and did not have the cdtA+ and cdtB- genes. This was the first report of highly virulent C. difficile strains from a Northern Irish pig herd.

Chapter 4 focused on Tractidigestivibacter scatoligenes, highlighting its resistance to both Trimethoprim and Streptomycin. This chapter also detailed T. scatoligenes high tolerance to p-cresol, with growth not significantly affected until a level of 0.125% v/v p-cresol and sustained growth observed in concentrations of up to 0.25% v/v p-cresol. This tolerance surpasses that of many other gut microbes, potentially conferring a competitive growth advantage. Proteomic analysis following p-cresol exposure triggered an upregulation in proteins related to cell wall repair, detoxification, aromatic compound degradation and a shift to alternative nutrient sources. These findings underscore the importance of characterizing novel gut microbes to better understand their roles in antimicrobial resistance and gut ecosystem dynamics, with implications for both animal and human health.

Date of Award	Dec 2025
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Agriculture & Horticulture Development Board
Supervisor	Elizabeth Magowan (Supervisor), Katerina Theodoridou (Supervisor) & Geoff McMullan (Supervisor)