From windows of threat to windows of opportunity : Housing management and nutritional interventions in early life toimprove pig health by shaping the gut microbiota, immune status and welfare

Weaning-associated environmental, psychological, and nutritional stressors can disrupt piglets’ gastrointestinal health and thus compromise their growth performance. Antimicrobials are used to sustain herd health during this stage. A multifaceted integrated approach is required to minimized reliance on antimicrobials usage for the development of more sustainable livestock production systems. In this thesis we aimed to evaluate effects of two such approaches. First, we investigated the effects of two housing conditions, i.e., conventional housing: (CH) versus enriched housing (EH), on welfare, immune status and gut microbiota from birth to 61 days. Our findings confirmed that EH pigs exhibited better welfare and immune status compared to CH pigs. EH pigs demonstrated increased percentages of T cells and cytotoxic T cells in peripheral blood, and higher ex vivo secretion of IL1ß and TNF-alpha after lipopolysaccharide stimulation. Additionally, the enriched house accelerated the maturation of pre-weaning gut microbiota, leading to increased relative abundance of bacterial groups involved in fibre degradation, such as Prevotella_2, Christensenellaceae_R_7_group and Ruminococcus gauvreauii group. Second, we evaluated the effects of supplementation of a potential postbiotic, rye overgrown with mycelium (ROM) of mushroom Agaricus subrufescens, on intestinal microbiota colonization and immune system development. Piglets received ROM or a tap water placebo every other day from day 2 to day 44. Eight animals per treatment were dissected on days 27, 44 and 70. Our findings revealed that pre-weaning faecal microbiota was more homologous in ROM pigs, with a prolonged effect on jejunal/caecal microbiota composition post-intervention. ROM supplementation primarily influenced the pig intestinal immune development. For instance, in the ileum, only a few genes were regulated in the control group from day 27 to day 44 post-weaning. In contrast, ROM pigs exhibited upregulated genes related to Toll-like receptor signaling, inflammatory responses, redox signaling, and apoptosis pathways. Moreover, ROM animals showed higher NK cell activation in blood and enhanced IL-10 production in ex vivo stimulated MLN cells before weaning. Lastly, we investigated bioactive carbohydrate-related compounds in ROM, using cytokine induction in chicken immune cells. Fractionation of rye and ROM and subsequent testing fractions on macrophage cell line HD11 showed that IL-12p40 production was mainly induced by hot water-soluble solids (HWSS) with ROM-HWSS more active than rye-HWSS. Stimulation of chicken splenocytes further confirmed their immunomodulatory capacity. Rye- and ROM-HWSS > 10 kDa (bioactive polymers) mainly consisted of arabinoxylan and glucan with smaller and variable amounts of protein and ferulic acid. NaOH treatment (0.1M) substantially reduced IL-12p40 induction by HWSS fractions and removed some ferulic ester groups, suggesting that feruloylated arabinoxylan structures contribute to IL-12p40 induction. Degradation of arabinoxylan, glucan and fructan in the HWSS fractions with specific enzymes did not affect IL-12p40 induction. Protease, chitosanase and Driselase treatments reduced IL-12p40 induction in ROM-HWSS, suggesting that mycelial compounds (e.g., protein, chitosan and galactan/mannan) may (also) contribute to the bioactivity. Overall, the findings of this thesis indicate that timely interventions through enriched housing and functional nutrition based on Agaricus subrufescens after birth can promote healthier, more resilient pigs, and thus better prepare them for the weaning transition.