Exploring the potential to improve the gut microbiome of broiler chickens using selenium nanoparticle supplements

The poultry industry has rapidly grown in the last few years with a focus in improving growth and productivity of broiler chickens, with performance assessed on measures such as feed conversion ratio, body weight gain and good immunity. The incorporation of antibiotics and feed additives in poultry diets, have been implemented for years to ensure the maintenance of poultry health with a focus on the control and reduction of zoonotic pathogens. In the last few years, however, key issues surrounding the antimicrobial resistance of antibiotics have urged for alternative supplementations. Nanoparticles (NPs) of silver and other metals have been heavily used in the poultry industry to improve the growth and performance of birds. Whilst successful, metal NPs exhibited higher toxicity at the higher surface to volume ratio, especially with the use of silver. This study proposes the use of NPs of essential metals and natural compounds to safely deliver nutrients, resulting in positive impacts on health and productivity with little to no toxic effects. Selenium is an essential mineral, required for the proper functioning of the immunity and is an important element in the first cell line of defence in the body. The work described in this thesis explores the ability of selenium NPs to improve the health and growth of broiler chickens by modulating their gut microbiome and metabolome, without the toxic effects observed with silver. Selenium NPs were synthesised using a simple chemical reduction method and a full characterisation was performed, assessing the physicochemical properties of the NP. Selenium NPs were then compared in an animal trial against two commonly used selenium additives in the poultry industry, sodium selenite (inorganic selenium) and selenomethionine (organic selenium). The performance of the birds was assessed based on body weight gain, the gut microbial composition and metabolite production. The toxicity of NPs was further investigated by quantifying selenium concentration in various tissues, along with a detailed histopathological assessment. Results show selenium NPs completely altered the gut microbial ecology at high concentration, with a strong correlation observed between Faecalibacterium prausnitzii abundance and increasing concentration of selenium NPs. Selenium NPs additionally increased villus height/crypt ratio associated with enhanced absorption in the small intestine and an overall increase of healthy colonic metabolites. Finally, an in vitro study demonstrated the ability of selenium NPs to reduce emerging pathogenic Enterococcus cecorum species. This thesis demonstrates the prospective ability of selenium NPs as alternatives to antibiotics and bulk supplementation, resulting in an improvement of health and performance of broiler chickens in the poultry industry.