Effects Of Dietary Electrolyte Balance And Iron On Intestinal Health And The Underlying Mechanism Of Pigs

The gut has functions of digestion and absorption,flora balance and immune regulation.Intestinal health depends on a healthy intestinal microflora and the integrity of the intestinal barrier,which is the key to maintaining animal health and improving production performance.Therefore,under the background of Infection with prohibiting the addition of antibiotics in feed and ecological breeding,it is particularly important and urgent to develop nutritional measures to improve the intestinal health of pigs and promote green and healthy breeding of pigs.Weaning of piglets significantly changed the structure and function of small intestine,impaired intestinal barrier function and intestinal microflora,resulting in the occurrence of post-weaning diarrhoeas.Dietary electrolyte balance(d EB)and citric acid(CA)play an important role in improving growth performance of weaned piglets.However,fewer experiments have been conducted on the effects and interaction of d EB and CA on the intestinal development,barrier function and microbiota of weaned piglets.In addition,iron is also an important nutrient affecting intestinal health.Iron overload produces large amounts of reactive oxygen species,thus triggering oxidative stress,destroying intestinal barrier function and changing microbial composition.Moreover,grains that are commonly used in pigs'diets generally have substantial levels of native Fe,which means that the total Fe levels(native plus supplemental levels)in the diet may higher than the pigs'needs,but whether this will lead to iron overload is unknown.Therefore,this study includes the following two experiments:(1)Weaned piglets are used to investigate the effects and interaction of d EB and CA on the growth performance,intestinal barrier function and microbiota,so as to provide reference data for rational application of d EB and CA in weaned piglets breeding.(2)Growing-finishing pigs are used to explore the molecular mechanism of the effects of dietary iron level on intestinal function and microbiota,and to provide reference for the rational application of Fe in the diet of growing-finishing pigs,and further contribute to understanding these aspects in humans.Experiment 1 Effects and interaction of dietary electrolyte balance and citric acid on growth performance,intestinal function and microbiota of weaned pigletsA total of fifty-six piglets(6.26±0.64 kg;Duroc×Landrace×Yorkshire)weaned at 21 days of age were randomly divided into 8 experimental groups according to their weight,each group of 7 pigs,and fed in a single pen.A 2×4factorial arrangement was used to design the diets:4 levels of d EB(-50,100,250and 400 m Eq/kg)and 2 concentrations of CA(0 and 0.3%).The concentration of Na,K and Cl in the ingredient was fully considered in the preparation of feed formula,and the d EB in the diet was adjusted by Ca Cl₂ and Na HCO₃.The formula of the d EB is:d EB(m Eq/kg)=[(Na×434.98)+(K×255.74)-(Cl×282.06)].The initial body weight,final body weight and daily feed intake of piglets were recorded.The experiment lasted for 14 days,and samples of blood,digesta and intestinal tract were collected at the end of the experiment.The results are as follows:1)Supplementation of 0.3%CA significantly increased villus height(VH)and villus height:crypt depth(VH:CD),and maltase activity in the jejunum(P<0.01).Piglets fed a 250 m Eq/kg diet increased VH and VH:CD in the duodenum(P<0.05).Dietary d EB and CA had significant interactional effects on the diarrhoea score and VH,CD,VH:CD in jejunum,VH,VH:CD in ileum,CD in cecum and colon,and sucrose,lactase and alkaline phosphatase activities in jejunum(P<0.05).2)Supplementation of 0.3%CA decreased the number of goblet cell in ileal crypt and Ki67-positive cells in jejunum,and the relative m RNA expression of CFTR,TNF-?,IFN-?,IL-1?,IL-10,ZO-1,occluding in jejunum(P<0.05).Ileal p H and plasma diamine oxidase significantly decreased in weaned piglets fed 250m Eq/kg d EB diet compared with those fed-50 and 400 m Eq/kg d EB diets(P<0.05).A 250 m Eq/kg d EB diet decreased the relative m RNA expression of IFN-?,IL-1?,IL-10 than 100 m Eq/kg d EB diet in jejunum(P<0.05).3)Supplementation of 0.3%CA decreased Shannon and simpson indices in ileum,and the relative abundances of Streptococcus in ileum and Prevotellaceae?NK3B31?group in colon(P<0.05).Piglets fed 250 m Eq/kg diet increased relative abundances of Firmicutes,Lactobacillus-rennini(P<0.05),decreased relative abundance of Proteobacteria,Veillonella,Actinobacillus and Escherichia-Shigella in ileum and butyric acid concentration in colon(P<0.05).The interaction effect between d EB and CA on the relative abundances of Cyanobacteria and Saccharibacteria in ileum and Firmicutes and Rikenellaceae?RC9?gut?group in colon were observed(P<0.05).In conclusion,a 250-m Eq/kg d EB diet reduced gastrointestinal p H and promoted the enrichment of beneficial microbes in the gut microbiota,thereby suppressing inflammation and harmful bacteria.Dietary d EB and CA had significant interactional effects on the diarrhoea score,intestinal morphology,intestinal digestive enzyme activity and composition of the intestinal microbiota of weaned piglets.Supplementation of 0.3%CA alleviated the negative effects of-50 m Eq/kg d EB on intestinal morphology development and intestinal barrier function and reduced diarrhea in piglets.Experiment 2 Effects of dietary iron level on intestinal function and microbiota in growing-finishing pigsA total of 1,200 barrows and gilts(27.74±0.28 kg BW;Large White×Landrace×Duroc)were housed in 40 pens of 30 pigs per pen(gilts and barrows in half),blocked by body weight and gender,and fed 5 experimental diets,which were control diet(basal diet with no Fe SO₄ supplementation)and the basal diet being supplemented with 150,300,450,or 600 mg/kg Fe SO₄ as Fe diets.The trial lasted for 100 days and was divided into the growing phase(27–60 kg of BW)for the first 50 days and the finishing phase(61–100 kg of BW)for the last50 days.And at the end of the experiment,8 pigs(barrows and gilts in half)were randomly selected from each treatment(selected 1 pig per pen)for digesta and intestinal samples collection.The results are as follows:1)The 300 mg/kg Fe group increased duodenal VH(P=0.024).Increasing Fe levels in the diets significantly increased transferrin(Tf)m RNA expression,decreased Eph B4 and Jagged 2 m RNA expression(linear,P<0.05).Compared with the other four groups,the control group showed significant increase in the transferrin receptor(TFRC)and divalent metal transporter 1(DMT1)m RNA expression(P<0.01).The apparent ileal digestibility of amino acids for pigs in the 450 and 600 mg/kg Fe groups were greater than for pigs in the control group(P<0.05).2)Increasing Fe levels in the diets tended to decrease chao1and ACE index,as well as the relative abundance of Firmicutes in ileum(P<0.10).Compared with control and 600 mg/kg Fe groups,300 mg/kg Fe group significantly increased the relative abundance of Lactobacillus(quadratic,P=0.037)in ileum.Compared with 600 mg/kg Fe group,300 mg/kg Fe group increased the relative abundance Leptotrichia,Negativibacillus,Roseburia,Succinivibrio in ileum and Butyrivibrio in colon,and decreased the abundance of Sediminibacterium,Pasteurella,Dielma,Parvimonas in ileum and Neisseria,Selenomonas in colon(P<0.05).A 300 mg/kg Fe diet tended to increase the concentrations of acetic acid,propanoic acid,pentanoic acid(P<0.10).In conclusion,iron homeostasis in growing-finishing pigs was strictly regulated.Dietary supplemen tation with 450-600 mg/kg Fe improved the digestive function of pigs.However,the high iron diet(600 mg/kg)changed the composition and structure of intestinal microflora and increased the abundance of intestinal inflammation-related microflora.Moreover,300mg/kg Fe supplementation increased the number of beneficial bacteria in the intestine and the concentration of SCFAs in the colon,thus improving the intestinal health.