Effect Of Graded Levels Of Dietary Threonine On The Growth Performance,Digestive And Absorptive Capacity,and Intestinal Barrier Function Of Jiang Catfish

The study was amid at to evaluate the effects of graded threonine（Thr）levels on the growth performance,digestive and absorptive capacity as well as intestinal barrier function under the normal condition and lipopolysaccharide（LPS）-challenged trial.A total of 1200 Jiang catfish Pelteobagrus vachelli♀×Leiocassis longirostris♂（14.19±0.06 g）were randomly distributed into six groups of each four replicates,and each replicate includes 50 catfish.Fish fed six diets containing graded levels of Thr at 9.5,11.5,13.5,15.4,17.4 and 19.3g kg^-1diet for 56 days,respectively.After feeding experiment,LPS-challenged experiment was carried out.The main results of the experiment are as follows:The growth experiment results showed that the appropriate Thr level in diet increased:（1）the percent weight gain and specific growth rate（P<0.05）;（2）the crude fat content,protein production value（PPV）,lipid production value（LPV）,and ash production value（APV）（P<0.05）;（3）the intestosomatic index（ISI）（P<0.05）;（4）the height of the intestinal folds and the number of goblet cells（P<0.05）;（5）the activities of pepsin in stomach,lipase,amylase,trypsin and chymotrypsin in the pancrea and intestine（P<0.05）;（6）the activities of intestinal alkaline phosphatase（AKP）,gamma-glutamyl transpeptidase（γ-GT）and Na⁺,K⁺-atpase（NKA）（P<0.05）.The growth experiment showed that the appropriate level of Thr:（1）improved the content of MDA and PC（P<0.05）,improved the GSH content and improved the activities of CAT,GST,GPx,GR（P<0.05）,inhibited m RNA expression levels of Cu Zn SOD,CAT,GPx,GST（P<0.05）;（2）up-regulated the m RNA expression levels of Occludin,ZO-1,ZO-2,Claundin2,Claundin3,Claundin7 and down-regulated MLCK m RNA levels（P<0.05）;（3）improved the m RNA expression levels of TOR and S6K1,while decreased4E-BP1 m RNA level（P<0.05）;（4）increased pro-inflammatory cytokines TNF-α,IL-10m RNA expression levels（P<0.05）,and decreased the expression level of the anti-inflammatory cytokines IL-10 and TGF-β1（P<0.05）,as well as increased My D88and MAPKp38 m RNA expression levels（P<0.05）.After LPS chanllenge,the appropriate level of threonine:（1）reduced the contents of ROS,MDA and PC in the intestine,improved the SOD,GR,GPx,GST activities and m RNA expression levels（P<0.05）;（2）improved the m RNA expression levels of ZO-1,ZO-2,Claundin2,Claundin3,Claundin7,and inhibited MLCK m RNA expression level（P<0.05）;（3）up-regulated the m RNA expression level of TOR and S6K1,and down-regulated the m RNA expression level of4E-BP1;（4）improved the IL-10 m RNA expression level（P<0.05）,decreased the m RNA expression level of pro-inflammatory cytokines IL-1β（P<0.05）,and improved the m RNA expression levels of My D88 and MAPKp38（P<0.05）;（5）reduced the m RNA expression levels of Casepase3 and Casepase9（P<0.05）.In conclusion,Thr enhances the growth performance by improving the digestive and absorptive capacity of the Jiang catfish.Thr can also maintain the intestinal barrier function by improving the antioxidant capacity,up-regulating tight junction protein m RNA expression levels,as well as regulating inflammation response under the normal condition and LPS-challenged trail.In this study,based on the SGR,the optimal Thr levels for Jiang catfish are estimated to be 13.77g kg^-1 diet,or 33.18 g kg^-1 CP。...