| With the banned of feed antibiotics and the surge in protein ingredients prices,China urgently needs to develop low-protein feeds without antibiotics,especially for weaned piglets.Weaning stress causes drastic changes in the intestinal morphology of piglets,leads to intestinal dysfunction.Therefore,essential nutrients such as vitamins and amino acids are urgently needed for regulation.Folic acid is a key factor affecting cell proliferation,and plays an important role in animal growth,metabolism,protein deposition and tissue synthesis.Methionine and valine play a key role in promoting the proliferation of intestinal cells,accelerating the renewal and regeneration of intestinal mucosa,regulating energy metabolism,promoting intestinal health and enhancing the immunity of pigs.Under the condition of low-protein diet without antibiotics,this study clarified the renewal law of intestinal epithelial cells of weaned piglets at different ages and conducted to reveal the intervention mechanism of several representative nutrients such as folate,the ratio of Met to SAA,and Val on the morphology and function of the small intestine of weaned piglets.Exp.1: This experiment was to explore the influence of weaning stress on the small intestine morphology and intestinal epithelial cell turnover in weaned piglets at different ages.It was randomly divided into 5 groups according to the principle of similar body weight(6.55 ± 0.15 kg)and half male and female.8replicates,each with 1 piglet.Samples were taken at 0,1,3,7 and 14 days after weaning.By detecting the morphological and structural changes of small intestinal villi,intestinal epithelial cell proliferation,differentiation and shedding etc.,orthogonal polynomial analysis was used to establish curve equations.The results showed that the development trend of VH,VW and VH/CD in the duodenum,jejunum and ileum of piglets from 0 to 14 days after weaning showed a quadratic curve.The number of Ki67-positive cells in the crypts of the duodenum,jejunum,and ileum decreased significantly on the 1st and 3rd days of weaning(P < 0.001),and gradually recovered on the 7th and 14 th days of weaning.However,the cell shedding rate of the jejunum increased significantly on the 7th day of weaning(P < 0.05);the number of piglet intestinal epithelial cells decreased significantly in the duodenum on the first day of weaning,and then gradually increased(P < 0.001);There was a significant decrease in the ileum on the 7th day(P < 0.05),and it recovered on the 14 th day.This trial found that the VH,CD and VW of the small intestine of weaned piglets were all affected by the age after weaning.The worst on the 6th day after weaning and basically recovered to the level before weaning on the 14 th day.The sharp decrease of VH in the jejunum of weaned piglets may be due to the increase in the shedding rate of intestinal epithelial cells and the decrease in the proliferation of crypt cells.Exp.2: The present study was conducted to evaluate the effect of dietary folic acid on the growth performance,intestinal morphology,and intestinal epithelial cells renewal in post-weaning piglets.Twenty-eight piglets(weaned at day 21,initial body weight of 6.73 ± 0.62 kg)were randomly allotted to 4 treatments with7 pens per diet and 1 piglet per pen.The piglets were fed the same antibiotic-free and zinc oxide-free basal diets supplemented with folic acid at 0,3,9,and 18mg/kg for 14 days.The results showed that dietary supplementation with folic acid increased villus height(VH),VH-to-crypt depth(VH:CD)ratio,villus surface area(VSA)(P < 0.05).The analyzed parameters ADG,serum urea nitrogen content(BUN),VH,VSA,and serum folate concentration(SF)responded linearly to the dietary folic acid concentration as assessed by two linear broken-line regression.Moreover,dietary supplementation with folic acid significantly increased the lactase and sucrase activities(P < 0.05)in the jejunal mucosa of weaned piglets.The m RNA expression of SLC6a19,SLC7a1,TNF-α,the number of Ki67-positive cells,and cell shedding rate had a significant linear contrast(P < 0.05),respectively in dietary folic acid groups.In conclusion,our results indicate that folic acid supplementation can improve the growth performance and intestinal morphology of weaned piglets by maintaining the balance of epithelial cell renewal.Exp.3: This study was conducted to evaluate the influence of different Met:SAA ratios on the intestinal morphology and function of weaned piglets.Twentyfour weaned piglets(boars,average weight 10.46 ± 0.34 kg)were randomly divided into 3 groups,and the ratio of Met: SAA in each group was 0.51(BD,basic diet)and 0.41(L-MR,low methionine)Ratio)and 0.61(H-MR,high methionine ratio).There were 8 replicates in each group,1 piglet in each replicate,and the period was 28 days.The results showed that compared with the BD group,the ADFI of the H-MR group was significantly lower(P < 0.05).The L-MR group up-regulated SNAT2 and SLC7A7 in the jejunal mucosa,and down-regulated the relative expression level of SLC7A9;the H-MR group down-regulated the relative expression level of SLC7A7 in the ileal mucosa(P < 0.05).Compared with the BD group and the H-MR group,the L-MR group significantly up-regulated the relative expression levels of ZO-1 in the duodenal mucosa,Claudin-1 and ZO-1in the jejunal mucosa(P < 0.05).This study showed that BD(0.51)had the best performance for piglets;L-MR(0.41)had a compensatory growth effect on piglets during the chronic recovery period of weaning stress,which could upregulate the expression levels of tight junction proteins and amino acid transporters in the duodenum and jejunum,thereby enhancing the intestinal barrier function and amino acid transport effectiveness.H-MR(0.61)reduced the ADFI of weaned piglets and could not alleviate weaning stress.Exp.4: This study was conducted to evaluate the effect of valine on the intestinal morphology and function of weaned piglets.144 weaned piglets(average weight 8.64 ± 0.41 kg)were randomly divided into 3 groups,basal diet group(BD group,dietary crude protein(CP)17%),0.15% V group(CP 16% +0.15%)Val)and 0.25% V(CP 15% + 0.25% Val),with 6 replicates in each group and 8 piglets in each replicate,and the period was 28 days.The results showed that compared with the BD group,the 0.15% V group had no significant differences in ADG,ADFI and FCR;the ADG and ADFI of the piglets in the 0.25%V group were significantly reduced(P < 0.05).The duodenal VW of the 0.15%V and 0.25% V groups was significantly reduced(P < 0.05).There were no significant differences in the m RNA expression levels of amino acid transporters,tight junction proteins and inflammatory factors in the duodenum and jejunum mucosa among the three groups.The results of showed that added 0.15% of valine to replace 1% of CP in the low-protein diet could maintain the small intestine morphology of weaned piglets,thereby maintaining performance.In summary,this thesis found the proliferation,differentiation and shedding of intestinal epithelial cells in weaned piglets.The worst on the 6th day after weaning and basically recovered on the 14 th day.The sharp decrease of VH in the jejunum of weaned piglets may be due to the increase in the shedding rate of intestinal epithelial cells and the decrease in the proliferation of crypt cells.From the aspect of cell biology,it reveals the influence of early weaning stress on the morphological changes of small intestine in weaned.Folic acid(4.42 mg/kg)in the diet could improve the growth performance of weaned piglets,and folate could regulate the renewal of jejunal epithelial cells to maintain the jejunum shape and mucosal enzyme activity.Moreover,L-MR(0.41)could improve the intestinal barrier function and amino acid transporter,which good for the compensatory growth of weaned piglets.H-MR(0.51)will affect the ADFI of weaned piglets.At last,added 0.15% Val to protein-restricted diet could maintain the intestinal morphology of weaned piglets,thereby maintaining performance. |
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