Corn Starch Structure, Extrusion And Enzyme Preparation Affected Digestion Of Corn-soya Based Diets By Pigs

In vitro and in vivo studies were conducted to investigate the effect of corn starch structure (amylase amylopectin ratio, AM/AP), corn extrusion and different enzyme blends on digestibilities of pig diets and ileal digesta bacterial community, which may provide reference to reduce corn nutritive variation and improve nutritive value of corn. This study has three parts. In first part, the effects of corn starch structure and the strorage duration of extruded corn on resistant starch formation and starch digestibility were investigated initially. In second part, the diets were incubated in sextuple with the in vitro two-stage enzyme incubation and dialysis procedures (in vitro method), and digestibilities of proximal nutrients of corn/soya based diets in terms of of dry matter, crude protein, starch, NDF and energy were determined to decide the optimal dosage of three enzymes. Further investigation was done on the effects of corn extrusion, phytase and its combination with amylase, protease and xylanase blend on the digestibilities of proximal nutrients of corn/soya based diets. Following experiment by in vitro and T-canula (in vivo) were conducted to find the effects of enzyme addition and corn extrusion on ileal digestibilities of proximal nutrients of corn/soya based diets and ileal digesta bacteria comunity, and also established regression relationships between digestibilities in vitro and in vivo to validate the effect of enzyme screened out by in vitro. In third part, based on the experiments above, the effects of corn extrusion and enzyme inclusion on the digestibilities of different statch structure (AM/AP) corn/soya based diets were compared. The main results are as followings:In First part, the effects of AM/AP and storage duration on formation of resistant starch and starch digestibility of extruded corn were investigated. Three corn samples with high, medium and low AM/AP (0.39,0.44, and 0.6) selected from 76 corn samples are extruded and stored in Ow, 1w,2w,3w and 4w at temperature 15℃and humidity 80%RH. In this experiment, extruded corn with higher AM/AP has the higher resistant starch formation and lower starch digestibility (P<0.01). And with the extended storage period from Ow to 4w, the resistant starch content of extruded corn was increased significantly and starch digestibility was decreased (P<0.05). Conclusion:corn AM/AP and extrude corn storage condition increased the resistant starch content and decreased the corn starch digestibility in vitro. In second part, Exp.1 the effects of enzyme blends (amylase, protease and xylanase) at different dosage rates [(high (H) vs medium (M) vs low (L)] on the digestibility were investigated in vitro using a two-stage enzyme incubation method to decide the optimal dosage of enzymes. The digestibilities of starch and NDF were both higher in H-and M-enzyme diets than in L-enzyme and control diets (P<0.05). Though the CAD of DM, GE, starch and NDF did not differ between H-and M-enzyme diets, the CP digestibilities was higher in H-enzyme than in M-enzyme diets(P<0.05). Conclusion:Medium level of amylase and xylanase is optimal to the corn/soya based diets.Experiment 2 was designed to examine the effects of corn extrusion, the addition of phytase and its combination with H-and M-enzyme on the digestibilities of dietary components based on the results of exreriment 1 to provide theory basis for improving corn nutritive value. In this experiment M-levels of xylanase and amylase were included in both the H-and M-enzyme blends, with protease dosage being held the same in each blend as in Exp.1. The digestibilities of all dietary components evaluated was higher (P<0.05) in Extruded than in nEXd corn diets. For nEXd corn diets, the combination of phytase with M-and H-enzymes resulted in a higher (P<0.05) digestibilities of GE, CP, NDF and starch than did phytase addition alone. In Extruded or nEXd the digestibilities of starch and NDF was higher (P<0.05) in phytase, H-and M-and phytase combined with H-and M-enzyme compared to the control diet. Conclusion:extrusion improved digestibility of the diets. The combination phytase and xylanase, amylase, protease was demonstrated to be more effective in improving the nutrient digestibility than did any of the single enzyme addition.In Exp.3, both in vitro and in vivo trials were conducted to evaluate responses of corn/soya based diets to the corn extrusion and the addition of phytase, H-and M-enzyme blends. Five cannulated pigs were fed five diets according to a 5×5 Latin square design. Similar to the results observed in vitro and in vivo trial. The Extruded corn diet had higher (P<0.05) digestibilities of DM, CP, starch, NDF and GE than nEXd corn diets. M-and H-enzyme addition both resulted in increased DM and CP digestibilities of nEXd corn diets. The digestibilities of amino acids of nEXd corn diets with H-enzyme addition was comparable with that of the Extruded corn diet (P<0.05), and was higher (P<0.05) than that of the nEXd corn diet except for Met, Thr, Trp and Cys. Compared to the nEXd, extrusion of corn improved the digestibilities of CP, starch and GE in feces. These results suggest that extrusion and multiple enzyme addition are-effective ways to improve the nutritional value of corn-based diets for pigs. There was a close linear relationship between the digestibilites in vitro and in vivo.Similarity analysis of bacterial community DGGE profiles from ileal digesta indicated low similarity of among the treatments. The diversity index of bacterial community in H-enzyme was significantly lower than the control (P<0.05), suggesting the enzyme inclusion had a noticeable effect on bacterial community of pig ileum.In third part, an in vivo trial was conducted to evaluate responses of corn/soya based diets to the starch structure, corn extrusion and the addition of H-enzyme blend in Exp.3 of the second part. Six cannulated pigs were fed-six diets according to a 6×6 Latin square design. Regardless of enzyme inclusion or AM/AP, corn extrusion increased the ileal starch and GE digestibilities corn/soya based diets of pigs. The lower AM/AP corn/soya based diets has higher ileal starch and GE digestibilities. The results showed that corn extrusion and lower AM/AP ratio increased the ileal starch and GE digestibilities of cron/soya based diets of pigs, but Enzyme addition has no effects on the ileal starch and GE digestibility.Conclusions can be drawn from results above:Corn starch amylose/amylopectin ratio has significant effects on the pig ileal starch and energy digestibility. Corn starch amylose/amylopectin ratio is an important factor that affects corn quality. Corn extrusion improved the digestibilities of the weaned pig corn/soya based diets. Optimal Enzyme type and inclusion rate increased the ileal DM, CP and most AA digestibilities and decreased ileal bacterial community of weaned pigs. The in vitro method can be used to predict the nutrient digestibilities by pigs to increase the speed and efficiency of enzyme selection...