Effect Of Adding Protease In Different Protein Levels Diets On Performance And Digestive Physiology Of Broilers

The purpose of this study was to investigate the effects of dietary protein levels and exogenous protease on performance, carcass performance, nutrition utilization, serum biochemical indices, digestive physiology and immune performance in broilers. A 3×3 factorial design with 3 CP levels (starter 21%,20%,and19%;grower 19%,18%, and 17%) and 3 protease levels (0,150, and 300mg/kg, enzyme activity unit 1×105U/g). High CP diet was a positive control (PC), low CP diets were two negative control (NC1、NC2).1,080 1-day-old Arbor Acres(AA) broilers were randomly assigned to 9 treatments with 6 replicates of 20 broilers(male and female in half). A metabolic experiment was conducted after growth experiment.The results showed as follows:1.NC1 and NC2 significantly decreased body weigh (BW) of 21d (P<0.05) and average daily gain(ADG) of 1-21 d (P<0.05), compared with NC1, NC2 significantly decreased BW and ADG of these stage. Compared with PC and NC1, NC2 decreased BW of 42d and ADG of 1-42d. NC2 significantly decreased average daily feed intake (ADFI) of 1-21d(P<0.05). With the decrease of protein levels, feed to gain (F/G) was significantly improved (P<0.05).300mg/kg protease group significantly decreased F/G of 1-21d (P<0.05). Compared with NC1, NC2 significantly improved mortality and cull rate. There were no significantly difference observed in carcass performance index.2.NC1 tend to decrease the digestibility of protein (P>0.05),while NC2 significantly decreased the digestibility of protein (P<0.05).150mg/kg protease group tend to improve the digestibility of protein, while NC2 significantly improved the digestibility of protein (P<0.05).NC2 significantly decreased digestibility of Thr、Ser、Gly、Tyr、Phe respectively (P<0.05) and significantly improved digestibility of Ala、Val (P<.05)。 150mg/kg protease group significantly improved digestibility of Arg(P<0.05). there didn’t observe significantly difference of amino acid affected by protease. The interaction between protein and protease was observed significantly of Ala,Val,Ile,Leu,Tyr,Pro respectively (P<0.05)。3. There was no significant difference on immune performance for protease, protein or their interaction (P>0.05)4.Compared with Omg/kg protease group,300mg/kg protease group significantly decreased MDA (P=0.047) and improved GSH-Px (P=0.023)at 21dAt 42d,there was no significant difference on GSH-Px. SOD, MDA for protease or the interaction.NC2 decreased GSH-Px significantly(P<0.05). Compared with 0,150mg/kg protease group, 300mg/kg protease group significantly decreased Cre of serum at 21d. NC1,NC2 significantly decreased ALB(P<0.05) at 42d,NCl significantly decreased GLB(P<0.05), no significant difference observed between NC2 and PC.5. With the decrease of protein, the trypsin activity in pancreas and duodenum at 21 d and at 42d in NC2 was significantly decreased. The trypsin activity in pancreas of 21 d was significantly improved in NC1+300mg/kg protease.Trypsin activity in pancreas at 42d was significantly improved by the addition of 300mg/kg protease (P=0.026)6. NC2 significantly decreased VH and V/C of duodenum, jejunum, ileum respectively (P<0,05) at 21 d.300mg/kg protease supplement significantly improved VH of duodenum, jejunm, ileum respectively(P<0.05), also improved V/C of duodenum (P<0.05) at 21 d.150mg/kg protease supplement significantly improved VH of duodenum, jejunum (P<0.05), also significantly improved ileum V/C (P<0.05) of 21d.NC2 significantly decreased VH, V/C of duodenum, jejunum, ileum respectively, also significantly decreased V/C of ileum at 42d.There was no significant difference on small intestine morphology for protease and no significant difference on small intestine morphology for interaction.7.300mg/kg protease supplement can significantly increase the profit, especially when added to PC.To sum up, exogenous protease may stimulate endogenous trypsin, promote the intestine morphology growth, improve digestibility of protein,improve broiler serum antioxidant to get better healthy, rise feed to gain ratio, and get more profit. The better dose of protease should be 300mg/kg in this experiment.