Unveiling Regulatory Mechanisms of Citrus Pectin on Intestinal Immunity in Piglets | Dévoilement des mécanismes de régulation de la pectine d'agrumes sur l'immunité intestinale chez les porcelets

China is the largest pig-raising country globally. In 2022, global pork production reached approximately 125 million tons, with China accounting for 55.41 million tons, equivalent to around 44% of the total production. Despite being the largest consumer of pork, China lags behind as an advanced pig-raising country. Compared with developed countries in the livestock industry, the average number of live piglets contributed by sows of the same breed in China is only 18-19 piglets per year, which is significantly lower than the average of 24-25 piglets in developed countries such as Denmark, the Netherlands, and France. This lower number can be explained by the combination of lower proliferating sows and higher early life mortality. Especially this high mortality rate of weaned piglets is an important factor restricting the pig breeding industry, and there is room for improvement. Young animals are more susceptible to the external environment, which can disrupt the gut microbial composition and result in pathogen overgrowth, leading to intestinal inflammation and diseases. Farmers have traditionally used antibiotics added to feed to help piglets overcome this critical stage. However, since Sweden took the lead in completely banning the use of antibiotics in feed in 1986, followed by Denmark and other EU countries, there has been a global trend towards antibiotic restrictions. By 2020, China had also joined the wave of comprehensive antibiotic bans. Pectin, as a plant-derived polysaccharide, is one of the seventh major categories of nutrients known as dietary fiber. It has a direct and significant impact on both the intestinal mucosal layer and microbiota, exhibiting preventive effects against diarrhea, promoting growth, and regulating immunity in livestock. However, the mechanisms underlying the regulatory effects of dietary fiber on the intestinal function of livestock remain unknown. Therefore, the purpose of this study is: 1) What are the effects of pectin on jejunal development, gut microbiota, and indole-like metabolites in healthy piglets, and mucosal immunity in healthy piglets? 2) After piglets fed pectin are injected with LPS, what effect will pectin have on growth performance and immune tolerance of piglets? Here we thus address the effect of pectin in pigs undergoing a model of inflammation 3) What is the effect of pectin on the cecal morphology, microbiota structure, and microbial metabolites of LPS-challenged piglet models? For the first objective, sixteen 21-day-old crossbred barrows (6.77 ± 0.92 kg; Duroc × Landrace × Yorkshire) were randomly assigned to two diets, with eight piglets per group. After a 3-day adaptation period, the piglets were fed a diet containing either 5% microcrystalline cellulose (control group) or 5% pectin (treatment group) for 3 weeks. The results demonstrated that pectin supplementation improved intestinal integrity, reduced inflammatory response, and down-regulated the expression of proinflammatory cytokines in the mucosa of the jejunum. Furthermore, pectin supplementation altered the jejunal microbiome and tryptophan-related metabolites in piglets, enhancing the AhR-IL22-STAT3 signaling pathway. Building on the first experiment, the second experiment aimed to investigate the resistance of piglets fed with pectin to LPS-induced stress. Twenty-four piglets (6.77 ± 0.92 kg BW; Duroc × Landrace × Large White; barrows; 21 days old) were randomly assigned to three groups: control, LPS-challenged, and pectin-LPS. The piglets received LPS or saline injections on days 14 and 21 of the experiment. The addition of pectin promotes the villus height in the ileum of piglets. At the same time, it restores the changes in tight junction proteins and inflammatory factors induced by LPS, thereby attenuating the inflammation caused by LPS stimulation in the small intestine. Additionally, it improved the mucin barrier function, increased MUC2 mRNA expression, and modulated the gut microbiota composition, reducing harmful bacteria and increasing beneficial bacteria and short-chain fatty acids (SCFAs) production. The third experiment focused on the cecum, as pectin is a dietary fiber known for its fermentation capability. Twenty-four piglets (Yorkshire × Landrace, 6.77 ± 0.92 kg) were divided into three groups: control, LPS-challenged, and pectin-LPS, with eight replicates per group. The piglets were fed corn-soybean meal diets containing 5% citrus pectin or 5% microcrystalline cellulose. Pectin supplementation mitigated the cecal morphological damage induced by LPS, improved the expression of tight junction proteins, mucin, and anti-inflammatory cytokines, while reducing proinflammatory cytokines. Pectin also modulated the gut microbiota composition, enriching beneficial bacteria and SCFAs, and activating relevant receptors. In summary, this thesis focused on the intestinal development, microbiota, and immune response of piglets at different gut segments (jejunum, ileum, and cecum). It explores the effects of pectin on piglets in healthy and non-healthy conditions and provides valuable insights into the potential benefits of pectin as an alternative to antibiotics in piglet feed.