Effects Of Dietary Energy Sources On Nitrogen Utilization In Finishing Pigs

This study was conducted to investigate the effects of dietary energy sources on nutrient of nitrogen utilization in finishing pigs.By measuring nutrient apparent digestibility,blood biochemical indices,gastrointestinal digestive enzymes,mRNA levels of glucose transporter,amino acid transporters and receptors in gastrointestinal tract,the mRNA levels and protein levels of crucial factors in protein synthesis and protein degradation signaling pathway,to explore the effects of dietary energy sources on protein metabolism in liver and skeletal muscle of finishing pigs,the results of this study could provide a more rational energy of diet for ante-mortem nutritional regulation technology.This study includes three parts:1.Effects of dietary energy sources on nutrient apparent digestibility,blood biochemical indices and serum hormones levels in finishing pigs.72 castrated barrows(Duroc × Landrace × Yorkshire)with similar initial body weight(average BW = 65.0 ±2.0 kg)were randomly allotted into three iso-energetic and iso-nitrogenous diets.Each group has 3 replicates of 8 pigs.Diet A was the control group,which the content of starch is 44.1%.And the content of starch in diet B and diet C was reduced about 15%or 30%based on the content of starch in diet A.The content of starch,crude fat and neutral detergent fiber(NDF)in diet A was 44.1%,5.9%and 12.6%,in diet B is 37.6%,9.5%and 15.4%;in diet C is 30.9%,14.3%and 17.8%.The preliminary trial lasted for 7d,and the trial lasted for 28d.The results in this study showed that:diet C group significantly decreased dry matter(DM),crude protein(CP),Ash apparent digestibility and T4 content(P<0.05),extremely significant decreased the serum contents of glucose,T3 and IGF-1(P<0.01)in comparison to diet A group in the serum of finishing pigs.Moreover,compared with diet A gourp,diet C group significantly increased LDH in the serum of finishing pigs(P<0.05).There was no difference in the serum contents of ALB,GLO,BUN,and the activity of GOT,GPT and ALP by feeding different dietary energy sources in finishing pigs.(P>0.05).In addition,there was no difference of nutrient apparent digestibility,serum biochemical indices and serum hormones levels between diet A group and diet B group in finishing pigs(P>.05).2.Effects of dietary energy sources on the activities of digestive enzymes,the mRNA expression of glucose transporter,amino acid receptors and transporters in gastrointestinal mucosa of finishing pigs.The results showed that:in the acitivities of digestive enzyme,compared with diet A group,diet C group extremely significant decreased the activities of amylase,maltase,and sucrose(P<0.01),decreased the activities of lactase and trypsin in intestinal mucosa of finishing pigs(P<0.05);in the mRNA expression of glucose transporter,amino acid receptors and transporters of gastrointestinal mucosa in finishing pigs,compared with diet A group,diet C group extremely significant increased the mRNA expression of SLC7A7,SLC6A19,SLC1A1 and GPRC6A(p<0.01),increased the mRNA expression of T1R1 and SLC1A5(,P<0.05),extremely significant decreased the mRNA expression of SGLT1,T1R2 and T1R3 in the mucosa of jejunum(P<0.01);meanwhile,diet C group extremely significant increased the mRNA expression of T1R1 and GPRC6A(P<0.01),extremely significant decreased the mRNA expression of T1R2 and T1R3 in mucosa of stomach in finishing pigs(P<0.01).But,diet B group had no effects on digestive enzymes activity,the mRNA expression of glucose transporters,amino acid receptors and transporters in comparsion to diet A group in gastrointestinal mucosa of finishing pigs(P>0.05).3.Dietary energy sources mediate the protein synthesis and degradation of skeletal muscle in finishing pigs through the mTOR signaling pathway and the UPP pathway.Compared with diet A group,diet C group had extremely significant decreased the mRNA expression of insulin receptor(IR)(P<0.01),decreased the mRNA expression of insulin receptor substrate(IRS)and protein kinase B(Akt)(P<0.05),increased the mRNA expression of Forkhead box 01(FoxO1),Forkhead box 04(Fox04),Muscle Ring finger 1(MuRF1)and Muscle atrophy F-box(MAFbx)in the skeletal muscle of finishing pigs(P<0.05).But different dietary energy sources had no effects on the mRNA expression of IR,IRS,IGF-1,IGF-1R in the liver of finishing pigs(P>0.05).At the same time,the protein levels of total and phosphorylated mammalian target of rapanycin(mTOR),eIF4E-binding protein 1(4E-BP1)and ribosomal protein s6 kinase 1(S6K1)were decreased(P<0.05),however,the protein levels of total and phosphorylated AMP-activated protein kinase(AMPK)were increased in diet C group in skeletal muscle of finishing pigs(P<0.05).In liver,different dietary energy sources had no effects on the protein levels of total and phosphorylated of mTOR,S6K1 and 4E-BP1(P>0.05).In conclusion:(1)The excessively decreased the contents of starch and the increased the contents of lipid and NDF in dietary(diet C group)had effects on the secretion of hormones in serum and decreased the nutrients apparent digestibility in finishing pigs.(2)Diet C group with lowest level of starch,highest levels of fat and NDF had negative effects on the digestive and absorptive nutrients in gastrointestinal tract of finishing pigs.(3)Diet C group with lowest level of starch,highest levels of fat and NDF suppressed protein synthesis and accelerated protein degradation in skeletal muscle of finishing pigs.In summary,these results indicated that the excessively decreased the contents of starch and increased the contents of lipid and NDF in dietary energy sources of finishing pigs had negative effects on the digestive and absorptive nutrients in gastrointestinal tract and protein metabolism in skeletal muscle of finishing pigs.