Effects Of Dietary Starch Types On Digestion,Metabolism And Related Metabolism Of Finishing Pigs

Feed nutrient factors have a significant effect on pig growth performance.Starch is the main source of pig dietary energy and accounts for half of the production costs.Previously Studies had shown that different types of starch could affect pig growth performance,digestion and metabolism.However,so far there have been few reports about the specific mechanisms that affect the digestion and metabolism of finishing pigs by different starch types.Thus,this study was aimed to investigate the effects of dietary starch types on digestion&metabolism and related metabolism of finishing pigs.By measuring serum biochemical indices and hormones levels,intestinal digestive enzymes,the mRNA levels of sweet taste receptors,glucose transporters and amino acid transporters in intestinal tract,crucial metabolism-related-enzymes,the mRNA levels of key metabolism-related-factors in liver,the mRNA levels of key factors in liver protein synthesis signaling pathway,and the mRNA levels of key factors in muscle protein synthesis and protein degradation signaling pathway,to explore the effects of dietary starch types on digestion&metabolism and related metabolism of finishing pigs,the results of this study could provide theoretical basis for the more rational allocation of diet.This study includes three parts:1.Effects of different starch types on serum biochemical indices,hormones levels and intestinal digestion&absorption of finishing pigsNinety barrows(68 ± 2.0 kg)were randomly allocated to three diets with five replicates of six pigs.The starch sources for the three experimental diets were pure waxy maize starch(WMS),non-waxy con starch(NMS)and pea starch(PS),and the proportions of amylose and amylopectin in the diet were 0.07,0.19,and 0.28.At the end of 28 days of treatments,two per pen(near to the average bodyweight of the pen)were weighed,slaughtered and the samples of jejunum mucosa and blood were collected.The results displayed that:in the serum biochemical indices,no significant effect was observed in the serum glucose level among groups(P>0.05).Compared with the WMS diet,PS and NMS diets significantly reduced the serum free fatty acid level(FFA)and lactic acid levels(P<0.05).Dietary starch types did not affect serum T3,T4,INS,and GC levels in finishing pigs(P>0.05).Dietary starch types had no significant effect in the activities of digestive enzymes in jejunum mucosa of finishing pigs(P>0.05).Compared with the WMS diet,the PS diet significantly decreased the mRNA levels of taste receptor type 1 member 2(T1R2),taste receptor type 1 member 3(T1R3),whereas significantly increased solute carrier family 1 member 5(SLC1A5)in jejunum mucosa(P<0.05);the NMS diet significantly increased the mRNA level of solute carrier family 7 member 7(SLC7A7)(P<0.05);PS and NMS diets reduced the mRNA levels of sodium/glucose cotransporter 1(SGLT1)and glucose transporter 2(GLUT2)(P<0.05).The results showed that:finishing pigs fed with PS diet(high amylose to amylopectin ratio diet)could reduce the mRNA expression of sweet taste receptors and glucose transporters,increase the mRNA expression of some amino acid transporters in jejunum mucosa,and then decrease the absorption of glucose,improved the absorption of amino acid.2.Effects of different starch types on liver nutrient metabolism of finishing pigsCompared with the WMS diet,the PS diet decreased the activities of glycogen phosphorylase,phosphoenolpyruvate carboxykinase and the expression of phosphoenolpyruvate carboxykinase 1 in liver(P<0.05).Moreover,the lipid contents,the concentrations of acetyl-CoA carboxylase and fatty acid synthetase,the activities of lipoprotein esterase and total lipase,the expression of sterol regulatory element binding protein-lc and HMGR in liver of PS and NMS diets were lower than those of WMS diet(P<0.05).The PS diet reduced the expressions of glutamate dehydrogenase and carbamoyl phosphate synthetase 1 in liver compared with the WMS diet(P<0.05).Compared with the WMS diet,the PS diet decreased the expression of the insulin receptor,and increased the expressions of mammalian target of rapamycin complex 1 and ribosomal protein S6 kinase?-1 in liver(P<0.05).The results showed that:PS diet could decrease liver lipid contents,the enzyme activities of gluconeogenesis and concentrations of lipid-related synthetase.PS diet could induce a down-regulation of lipogenesis and up-regulation of protein composition in liver of finishing pigs by altering the insulin/PI3K/mTOR signalling pathway.3.Effects of different starch types on the synthesis and degradation of skeletal muscle protein of finishing pigsNo significant effect was observed in the concentrations of the glutamate and glutamine,the mRNA levels of GS,GA,and GDH in muscle of finishing pig(P>0.05).Compared with the WMS diet,PS and NMS diets significantly reduced the mRNA level of GLUT4 in the muscle of the finishing pigs(P<0.05).There was no significant effect in the mRNA levels of IR,IRS and Akt in the muscle of finishing pigs among three groups(P>0.05),and the mRNA levels of mTORl,4E-BP1 and S6K1 were not significantly affected by dietary starch types(P>0.05).In the UPP pathway,compared with the WMS diet,the PS diet significantly reduced the mRNA levels of MAFBx and MUFR1 in the muscle of finishing pigs(P<0.05).The results showed that:No significant effect was observed in nitrogen metabolism and mTOR signaling pathway in muscle of finishing pigs among three groups.However,WMS diet(low amylose to amylopectin ratio diet)significantly increased the mRNA levels of GLUT4 as well as the key factors MAFBx and MUFR1 of the UPP pathway compared with other groups,which could lead to the degradation of skeletal muscle protein.