The role of Dietary Interventions in Broiler Intestinal Health and Immunity

The innate immune system represents the host’s initial defence mechanism which responds to a diverse range of antigenic stimuli. This response is characterised by the activation of pathogen recognition receptors upon recognition of microbial patterns. This action results in the activation of the transcription factor NF-κB, MAPK signalling pathways and the induction of pro-inflammatory cytokines. The gastrointestinal mucus layer serves as an essential innate barrier to pathogenic adhesion and subsequent infection. Dysregulation in the integrity or function of the mucosal layer has been implicated in malabsorption, leading to reduced animal productivity. The objective of the work described in this thesis was to evaluate the effect of dietary supplementation of mannan-rich natural formulations on broiler tissue morphology, mucin barrier integrity, digestive enzyme capacity, apoptotic and necroptotic cell death levels and the expression of inflammatory cytokines. Supplementation of diet with each mannan-rich fraction (MRF) increased villus height and villus surface area. In addition, crypt depth was increased upon dietary inclusion of naturally-derived additives. Dietary inclusion of mannan rich fraction (MRF) supplements (supplements 1 to 3) enhanced goblet cell density and mucus layer thickness. Incorporation of mannan-rich fraction 1 (MRF-1) and mannan-rich fraction 2 (MRF-2) enhanced the activities of digestive enzymes maltase, sucrase and alkaline phosphatase. The expression of apoptotic cell death markers (TUNEL staining and caspase-3 expression) was not altered statistically upon incorporation of dietary additives. Receptor interacting serine/threonine kinase 3 (RIPK3) expression was significantly decreased upon MRF-1 supplementation in the duodenum, jejunum and caecum. Supplementation of mannan rich fraction 3 (MRF-3) significantly enhanced protein expression levels of p-Akt. MRF-2 and MRF-3 dietary incorporation led to a significant decrease in RIPK3 protein expression levels. Dietary additive inclusion had little effect on serum and tissue lysate expression of inflammatory cytokines. The work in this thesis demonstrates a role for mannan-rich fractions in improving broiler tissue morphology, barrier integrity and digestive enzyme capacity, thus potentially enhancing overall broiler performance