| The malnutrition caused by decreased feed intake and dietary protein fermentation in hindgut are the main factors causing growth retardation,decreased feed conversion rate,gut dysfunction,increased morbidity and mortality of post-weaning piglets.The current researches on weaned piglets are primarily focused on how to alleviate the poor growth performance and gut dysfunction during the early post-weaning period.Research shows that low protein AA balanced diet could efficiently alleviate gut dysfunction of post-weaning piglets by decreasing gut protein fermentaion without comprimising the growth performance.However,research on how to improve the growth rate and feed conversion rate of piglets during the late post-weaning period is limited.Compensatory growth is a phenomenon that animals exhibit retarded growth due to limitation of a certain nutrient and accelerated growth in response to the nutrient realimentation.Research shows that protein restriction could induce compensatory growth of animals,improving feed conversion rate and growth rate.Therefore,this research first explored whether protein restriction and realimentation could induce compensatory growth of rats by investigating the effects of protein restriction and realimentation on growth performance,jejunal and colonic function,gut microbial composition and metabolism of rats.Afterwards,the compensatory growth induced by protein restriction and realimentation was applied to weaned piglets to improve feed conversion rate and growth rate of piglets during the late post-weaning period.The mechanisms of compensatory growth was revealed by thoroughly investigating the changes in gut digestive and absorptive function,gut immune function,gut microbiota and protein deposition in longissimus dorsi of piglets.1 The effects of protein restriction and realimentaion on growth performance,organ weight and blood hormone level48 Sprague-Dawley male rats,weaned at 21 days of age,were used in the study.18 rats were randomly selected to be fed with a NPD as a control group(CG),with 3 rats housed in a same cage.The remaining 30 rats(TGI)were randomly allocated into 6 cages and fed with LPD until experimental day 14,with 5 rats in each cage.On day 14,6 rats from the CG and the other 6 rats from the TGI were sacrificed for sampling.On the same day,the rats from the TGI were mixed and then randomly reassigned to a TGI(rats were continuously fed with the LPD)and a TG2(rats were fed with the NPD).On day 28 and 70,6 rats from each group were sacrificed for sampling.Rats were weighed regularly and the feed intake was recorded to calculate average daily gain(ADG),average daily feed intake(ADFI)and feed/gain ratio.The blood hormones were assayed and the weight of organs was recorded to calculate relative organ weight.Results showed that the body weight(BW)of rats in TGI was lower than the CG on day 14,28 and 70.However,the BW of rats in TG2 was lower than the CG on day 28,but it did not differ from the CG group on day 70,indicating that protein restriction inhibited the growth of rats and induced compensatory growth after protein realimentation.Moreover,the feed/gain ratio in TG2 was lower than CG during day 28-70.In addition,the organ weight of rats in TGI was lower than CG group.However,the organ weight of rats in TG2 was lower than the CG on day 28,but it did not differ from the CG group on day 70,indicating that protein restriction inhibited the growth of organs and induced compensatory growth of organs after protein realimentation.The relative weight of organs in TGI and TG2 was not different from CG.Finally,the rats in TGI had lower concentrations of serum growth hormone(GH)on day 14 and day 28 as well as lower serum insulin on day 70 compared with CG.However,rats in TG2 had higher serum GH on day 28 and decreased serum insulin on day 70 compared with CG,indicating that the changes in hormones were associated with the compensatory growth.In conclusion,protein restriction and realimentation could induce compensatory growth of weaned rats,inproving growth rate and decreasing feed/gain ratio.The compensatory growth of BW in rats was accompanied by compensatory growth in the weight of organs without affecting the relative organ weight.Moreover,the changes in serum hormones(GH and insulin)were associated with the compensatory growth.2 Effects of protein restriction and realimentation on jejunal function,microbial composition and metabolism in jejunum of ratsThe part analyzed the changes in mucosal morphology by HE staining,expression of genes related to gut function,jejunal microbiome and microbiota-derived metabolites.The results showed that the rats in the TG2 had improved jejunal morphology and increased expression of genes related to digestion,absorption and tight junction proteins on day 28 compared with the CG,promoting the compensatory growth,although they had temporarily impaired morphology and expression of these genes in the jejunum on day 14 in response to the LPD.However,the lower expression of genes related to nutrient absorption and undifferentiated villous height(VH)were observed in the jejunum of rats in the TG2 on day 70.In contrast,rats in the TG1 had lower VH on day 28 and day 70,despite the expression of absorptive genes were increased on day 28 compared with the CG.Additionally,dramatic microbial changes in the jejunum of compensatory-growth rats were observed,principally including Lactobacillus,Streptococcus,Corynebacterium and Staphylococcus.The correlation analysis revealed that the abundance of Lactobacillus,Streptococcus,Corynebacterium and Staphylococcus significantly correlated with the gene expression in the jejunum.In conclusion,the increased VH and improved expression of genes related to nutrient digestion and absorption as well as genes related to barrier function on day 28 in the jejunum of rats in TG2 promoted the compensatory growth.In addition,the abundance of Lactobacillus,Streptococcus,Corynebacterium and Staphylococcus significantly correlated with the gene expression in the jejunum.3 Effects of protein restriction and realimentation on colonic function,microbiome and microbial metabolism in rat colonThis part aims to investigate the effects of protein restriction and realimentation on mucosal immune function,microbiome and microbial metabolism in rat colon.The microbial composition and the concentrations of SCFAs and ammonia-N were analyzed in the colonic content.In addition,the expression of genes related to mucosal barrier function and innate immune function were determined.Results showed that protein restriction and realimentation caused significant changes in the relative abundance of bacterial groups in the colonic content,principally including the decreased abundance of Bacteroidetes and the increased abundance of Firmicutes and Actinobacteria.In addition,compared with CG,rats in TG2 had higher concentration of total SCFAs(particularly butyrate)in the colonic content on day 28,which benefitted the energy utilization and promoted compensatory growth.Finally,compared with CG,rats in TG2 had higher expression of barrier associated genes,TLRJ and TLR4 in the colonic mucosa on day 28 and 70,indicating improved mucosal immune function.However,rats in TG2 had higher expression of Tnf-? in the colonic mucosa than CG on day 70,suggesting that compensatory growth might induce inflammation in colonic mucosa in late life.In conclusion,protein restriction and realimentation caused significant changes in microbial composition in the colonic content of rats.The changes in microbiome were responsible for the increased production of total SCFAs,particularly butyrate.Meanwhile,protein restriction and realimentation caused increased expression of genes related to mucosal immune function.All these changes in colon promoted the compensatory growth of rats in TG2.4 Effects of protein restriction and realimentation on growth performance,apparent feed digestibility,jejunal digestive and absorptive function of weaned piglets36 piglets weaned at 28 days with an initial average body weight(BW)of 6.47±0.04 kg were randomly assigned to a control group(CG)and a testing group(TG),with 6 replicates(pens)in each group and 3 piglets in a pen.Piglets in CG group were fed with a normal protein diet(NPD)containing a protein level of 18.83%during the whole experiment.Piglets in TG group were fed with a low protein diet(LPD)containing a protein level of 13.05%from day 0-14 and were fed with the NPD from day 14-28.During the experiment,the diarrhea was monitored every day,the feed intake per pen was precisely recorded,the piglets were weighed and the faecal samples were collected every other day.The average daily feed intake(ADFI),average daily gain(ADG)and feed:gain ratio was calculated.The dry matter,crude protein and acid insoluble ash(AIA)in the feed and feces were determined to calculate the apparent digestibility and faecal nitrogen content.In addition,the jejunal mucosal morphology was observed and the activity of digestive enzymes and the expression of genes related to nutrient digestion and absorption were analyzed.Results showed that,compared with CG,piglets in TG had lower BW on day 14 and undifferentiated BW on day 28,suggesting that protein restriction and realimentation induced compensatory growth of piglets during late post-weaning period.Compared with CG,piglets in TG had lower ADG,higher feed:gain ratio and ADFI during day 0-14.However,the ADG of piglets in TG tended to increase and the feed:gain ratio was decreased compared with CG during day 14-28.Moreover,piglets in TG had higher DM and protein digestibility during day 0-14 than CG.Meanwhile,compared with CG,piglets in TG had lower faecal nitrogen content during day 0-14 and day 14-28,suggesting that protein restriction and realimentation could decrease nitrogen excretion.In addition,the increased villous height,increased activity and expression of APA and DPP-IV and increased expression of PepT-1 and Sglt1 in the jejunum of piglets in TG on day 28 suggested improved digestion and absorption function,which promoted the increased feed digestibility and the compensatory growth of piglets.In conclusion,protein restriction and realimentation could induce compensatory growth of piglets during late post-weaning period,improving growth rate and decreasing feed:gain ratio and faecal nitrogen excretion.In addition,the improved jejunal digestive and absorptive function during the protein realimentation period promoted the compensatory growth of piglets.5 Effects of protein restriction and realimentation on immune function and mcirobiome in piglet jejunum and colonThis part aims to investigate the effects of protein restriction and realimentation on immune function and microbiome in piglet jejunum and colon.The expression of genes and proteins related to mucosal barrier function and inflammation were determined by q-PCR,western blot and ELISA.The microbial composition in jejunal and colonic content and mucosa were revealed by 16S rDNA high throughput sequencing and the concentrations of SCFAs and ammonia-N were analyzed in the colonic content.Results showed that,piglets in TG had higher expression of Zo-1 in jejunum and higher expression of Occludin and Zo-1 in colon on day 14 and day 28 compared with the CG,suggesting that protein restriction and realimentation improved barrier function in jejunum and colon.In addition,compared with the CG,piglets in the TG had decreased expression of Tnf-? and Il-1? and increased expression of Il-10 on day 14 and decreased level of Il-1? on day 28 in jejunum.However,the concentrations of Tnf-?,Il-1? and Il-10 in colonic mucosa of piglets in the TG on day 28 were higher than those in the CG.These results indicated that protein restriction decreased inflammatory response in jejunum,while increased inflammatory response in colon on day 28.Meanwhile,protein restriction and realimentation caused significant changes in microbial composition in both jejunum and colon.In addition,piglets in the TG had lower concentrations of total branch chain fatty acids and ammonia-N in the colonic content on day 14 and day 28,indicating decreased protein fermentation.While piglets in the TG had higher concentration of total SCFAs(acetate,propionate and butyrate)compared with the CG,which might promote the energy utilization.In conclusion,protein restriction and realimentation improved the barrier function in jejunum and colon,decreased the inflammatory response in jejunum,while increased the inflammatory response in colon.In addition,protein restriction and realimentation caused significant changes in microbial composition in both jejunum and colon,improved the capability of microbiota in colonic content to metabolize carbohydrate,decreased protein fermentation in colon and increased the concentration of total SCFAs on day 28.These changes promoted the decreased diarrhea incidence and improved energy utilization,thus promoting the compensatory growth of piglets.6 Effects of protein restriction and realimentation on protein deposition in the longissimus dorsi of pigletsThis study aimed to investigate the effects of protein restriction and realimentation on protein deposition in the longissimus dorsi of piglets.Results showed that piglets in TG had decreased protein content in the longissimus dorsi on day 14 and undifferentiated protein content on day 28 compared with CG,suggesting that the protein deposition rate was inhibited during protein restriction and was increased during protein realimentation.In addition,compared with CG,piglets in TG had decreased level of GH and IGF-1 in the longissimus dorsi on day 14 and increased level of GH and IGF-1 in the longissimus dorsi on day 28,indicating that the changes in GH and IGF-1 level were associated with the protein metabolism in the longissimus dorsi.Further investigating the gene expression and protein expression of key proteins in the IGF-1 signaling pathway showed that,compared with CG,piglets in TG had higher expression of genes that promote protein synthesis(mTOR and AM)and protein degradation(4EBP1 and MAFbx)in the longissimus dorsi on day 14.However,the expression of genes that promote protein synthesis,including IGF-1,mTOR and Akt,was increased and the gene expression of MAFbx was decreased in the longissimus dorsi of piglets on day 28,promoting the protein deposition in the longissimus dorsi.In conclusion,protein restriction and realimentation caused increased protein deposition rate in the longissimus dorsi of piglets in TG during compensatory growth.The changes in GH and IGF-1 level as well as the changes in the gene expression of key proteins in IGF-1 signaling pathway were associated with the changed protein deposition rate in longissimus dorsi of piglets. |
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