Effect Of Low-protein Diet On Intestinal Morpholgoy,Digestive Enzymes,Gut Hormones,Gut Microbiota And Its Metabolites In Pigs

The shortage of high quality protein sources is a worldwide problem,especially in China.Globally,China is the largest soybean importer since 2002.Therefore,reducing the dietary protein content could effectively reduce pressure on protein ingredient supplies.In pig production,the dietary crude protein(CP)content can be reduced when the requirements for essential amino acids(EAA)and total nitrogen are met,because for pigs the need for dietary protein is essentially a need for amino acids(AA).Because of limited lysine content in corn,higher amount of soybean meal(SBM)was included in traditional corn-soybean meal(CSBM)diets to meet lysine requirement of pigs,which resulted in high CP levels.High-protein(HP)diets led to excesses of other EAA and excretion of excess nitrogen in feces and urine,resulting in lowering the efficiency of nitrogen utilization.However,the effect of low-protein diet and duration of feeding on intestinal physiology is not well known.This study investigated the effects of low protein diet supplemented with Lysine(Lys),Methionine(Met),Threonine(Thr),and Tryptophan(Trp)on small intestine morphology,enzyme activity,blood urea nitrogen,and gut microbiota and metabolites in weaned piglets,which potentially provide a foundation for using low-protein diet in practice.1 Effects of low protein diet on the intestinal morphology,digestive enzyme activity and gut hormones in weaned pigsThis study investigated the effects of low protein diet supplemented with Lysine(Lys),Methionine(Met),Threonine(Thr),and Tryptophan(Trp)on small intestine morphology,enzyme activity and blood urea nitrogen in weaned piglets.Eighteen weaned pigs weighing an average of 9.57 kg received one of three treatments:a normal protein diet with 20%CP(NP),a moderately reduced protein diet with 17%CP(MP),or a low protein diet with 14%CP(LP).All three diets were supplemented with Lys,Met,Thr,and Trp to meet essential amino acid(AA)requirements for post-weaned piglets according to the NRC(2012).Following a 45 day study period,piglets on the LP and MP diets demonstrated disturbed small intestinal morphology,with decreased villus heights and lower ratios of villus height to crypt depth(P<0.05);pepsin activity in the stomach was also reduced from these two groups(P<0.05).Increased plasma cholesterol and decreased blood urea nitrogen presented in the MP and LP groups compared with the NP group(P<0.05).Overall,gastrointestinal hormones were not affected by dietary protein levels with the exception of reduced somatostatin(SS)levels in the MP and LP groups.2 Effects of low protein diet on gut microbiota and its metabolites in weaned pigs This study investigated the effects of low protein diet supplemented with Lysine(Lys),Methionine(Met),Threonine(Thr),and Tryptophan(Trp)on gut microbiota and metabolites in weaned piglets.Eighteen weaned pigs weighing an average of 9.57 kg received one of three treatments:a normal protein diet with 20%CP(NP),a moderately reduced protein diet with 17%CP(MP),or a low protein diet with 14%CP(LP).All three diets were supplemented with Lys,Met,Thr,and Trp to meet essential amino acid(AA)requirements for post-weaned piglets according to the NRC(2012).Following a 45 day study period,jejunum and colon microbiota was not affected at either the phyla and genera level in any of the diets.Colonic ammonia nitrogen concentrations was reduced in MP and LP groups.Dietary protein level had no effect on short chain fatty acids(SCFA)or biogenic amines.Our data suggest that reducing dietary protein levels by 3%(MP)or 6%(LP)in weaned pigs has the potential to decrease nitrogen emissions and impaired digestive capacity.3 Effects of a long-term low-protein diet on intestinal morphology,digestive enzymes and gut hormone in pigsThe study was aimed to investigate the impact of a long-term low-protein diet on intestinal morphology,digestive enzymes and gut hormone in pigs.Eighteen Duroc ×Landrace × Yorkshire pigs(35 days of age,9.46±0.61 kg)were randomly allocated to three groups:normal protein diet(NP),moderately low-protein diet(MP,reducing protein by 3%of NP)and low protein diet(LP,reducing protein by 6%of NP).All three diets are supplemented with Lysine,Methionine,Tryptophan and Threonine to meet an ideal amino acid(AA)pattern according to NRC(2012).After 16 weeks trial,the results showed that feeding LP diet decreases villus height in duodenum and the ratio of villus height to crypt depth in jejunum(P<0.05);Activity of Pepsin and H+-K+-ATPase in stomach were increased in LP group(P<0.05).Decreased blood urea nitrogen and colonic ammonia nitrogen contents were found in LP group compared with NP group(P<0.05).Gastrointestinal hormones,such as,ghrelin,somatostatin,glucose-dependent insulin-tropic polypeptide(GIP),gastrin,were decreased by MP and LP diets(P<0.05).Leptin in LP was reduced and cholecystokinin in MP was increased(P<0.05),while PYY was not affected in MP and LP group.4 Effects of a long-term low-protein diet on colonic microbiota and its metabolites in pigsThe study was aimed to investigate the impact of a long-term low-protein diet on colonic microbiota and their fermentation metabolites in pigs.Eighteen Duroc x Landrace × Yorkshire pigs(35 days of age,9.46 ±0.61 kg)were randomly allocated to three groups:normal protein diet(NP),moderately low-protein diet(MP,reducing protein by 3%of NP)and low protein diet(LP,reducing protein by 6%of NP).All three diets are supplemented with Lysine,Methionine,Tryptophan and Threonine to meet an ideal amino acid(AA)pattern according to NRC(2012).After 16 weeks trial,the results showed that the colon microbiota was not affected in richness and diversity(P<0.05),when feeding a reduced protein diet either MP diet or LP diet.At genus level,the relative abundance of Streptococcus,Lactobacillus and Turicibacter was decreased as dietary protein was reduced,whereas Prevot.ella,Ruminococcus and and Lachnospira was increased in MP and LP group.Quantitative analysis showed that Bacteroides,Lactobacillus and Clostridium Cluster IV were decreased in LP group,Ruminococcus was increased in MP and LP group compared with NP group.Moreover,LP diets decreased short chain fatty acids(SCFA),such as acetate,isobutyrate and isovalerate,and ammonia were also reduced in LP diets.Tryptamine,putrescine and cadaverine were reduced in LP and MP diets.Our data suggest that reducing dietary protein level have potential to decrease nitrogen emission without compromising gut microbiota,however damage small intestinal morphology and pepsin activity in weaned pigs.In conclusion,reducing dietary protein level by 3%have no effect on pigs growth performance and intestinal physiology.However,decreasing protein level by 6%reduced the growth performance and impaired the intestinal physiology.Our data suggest that pigs canbe fed dietary protein with 3%less than NRC 2012 recommendation.