| Two hundred and forty healthy Arbor Acre(AA)male broilers(1-day old)with similar body weight were randomly allotted to 4 treatments,with 6 replicates of 10 broilers per replicate.The control treatment was fed with basal diet,and treatments were fed with the basal diets supplemented with 0.02%,0.04% and 0.06% quercetin for 6 weeks,respectively.The purpose of this experiment was to investigate the effects and mechanism of quercetin on protein digestion and utilization in AA broilers via determining apparent metabolic ratio of protein,blood biochemical indexes,activities of gastrointerstinal proteases,protein deposition of breast and thigh muscle,cecal microbiota and target of rapamycin(TOR)signaling pathway.Results showed that:(1)Effects of quercetin on apparent metabolic ratio of protein in AA broilers: compared with control,0.02% quercetin significantly increased apparent metabolic ratio of protein(P<0.05),and other two treatments had no significant changes(P>0.05).(2)Effects of quercetin on blood biochemical indexes in AA broilers: compared with control,0.02% quercetin significantly increased content of serum albumin(P<0.01);Three quercetin treatments had no significant effects on content of serum total protein and urea nitrogen(P>0.05).(3)Effects of quercetin on activities of gastrointestinal proteases in AA broilers: compared with control,0.02% quercetin significantly increased activity of pepsin(P<0.01);0.04% quercetin significantly decreased activity of chymotrypsin(P<0.05);Three quercetin treatments had no significant effect on activities of trypsin(P>0.05).(4)Effects of quercetin on protein deposition of skeletal muscle in AA broilers: compared with control,0.02% quercetin significantly increased total protein content of breast and thigh muscle(P<0.05,P<0.01).(5)Effects of quercetin on cecal microbiota in AA broilers: BLAST results showed that the main microflora in cecum of AA broilers included Proteobacteria(gamma-proteobacterales,Helicobacter and Campylobacter jejuni),Firmicutes(Clostridium),Bacteroidetes(Bacteroides)and Deferribacteres(Deferribacterales).Effects of quercetin on cecal microflora in AA broilers: compared with control,0.02% quercetin significantly decreased copies of Pseudomonas aeruginosa and Helicobacter pylori(P<0.05),Salmonella enterica,Staphylococcus aureus,Escherichia coli,Clostridium perfringens and Campylobacter jejuni(P<0.01),whereas significantly increased copies of Lactobacillus and Enterococcus faecalis(P<0.01).0.04% quercetin significantly decreased copies of Pseudomonas aeruginosa and Salmonella enterica(P<0.05),Staphylococcus aureus,Clostridium perfringens,Campylobacter jejuni and Helicobacter pylori(P<0.01),whereas significantly increased copies of Bifidobacterium(P<0.01).0.06% quercetin significantly decreased copies of Staphylococcus aureus,Helicobacter pylori(P<0.05),and Clostridium perfringens(P<0.01),whereas significantly increased copies of Bifidobacterium and total bacteria(P<0.05,P<0.01).(6)Effects of quercetin on Target of Rapamycin signaling pathway in AA broilers: compared with control,0.02% quercetin significantly increased mRNA expression of Phosphatidylinositol 3-kinase(PI3K)(P<0.05),TOR,Ribosomal Protein S6 Kinase(S6K1),Eukaryotic Elongation Factor 2(eEF2),Eukaryotic Translation Initiation factor 4B(eIF4B),Eukaryotic Translation Initiation Factor 4E(eIF4E)and Eukaryotic Translation Initiation Factor 4G(eIF4G)(P<0.01)in liver.0.04% quercetin significantly increased mRNA expression of eEF2(P<0.05),whereas significantly decreased mRNA expression of Eukaryotic Initiation Factor 4E Binding Protein1(4E-BP1)(P<0.05)and Eukaryotic Elongation Factor 2 Kinase(eEF2K)(P<0.01)in liver.0.06% quercetin significantly decreased mRNA expression of eEF2K(P<0.01)in liver.0.02% quercetin significantly increased mRNA expression of Insulin-like Growth Factors-1(IGF-1),Protein Kinase B(PKB/AKT)and eIF4B(P<0.05),eEF2,eIF4 E and eIF4G(P<0.01)in thigh muscle.0.04% quercetin significantly increased mRNA expression of PI3 K,TOR,eEF2 and eIF4G(P<0.05),whereas significantly decreased mRNA expression of 4E-BP1(P<0.05)in thigh muscle.0.06% quercetin significantly increased mRNA expression of PI3K(P<0.05)in thigh muscle.0.02% quercetin significantly increased mRNA expression of IGF-1,AKT,S6K1,eEF2,eIF4 B,eIF4E and eIF4G(P<0.01)in breast muscle.0.04% quercetin significantly increased mRNA expression of IGF-1(P<0.05)in breast muscle.0.06% quercetin significantly increased mRNA expression of PI3 K,eEF2,eIF4B(P<0.05)and TOR(P<0.01),whereas significantly decreased mRNA expression of eEF2 K and eIF4G(P<0.05)in breast muscle.In conclusion,appropriate dosage of quercetin increased apparent metabolic ratio of protein in AA broilers via regulating activities of gastrointestinal proteases,protein metabolism of organism,cecal microbiota and TOR signaling pathway.Under this experimental condition,the optimum dosage of quercetin for promoting protein digestion and utilization in AA broilers was 0.02% in the basal diet. |
