| The objective of this study was to characterize the effects of protease, organic acid salt and protease-organic acid salt combination on growth performance, body composition, immunity, digestive enzymes, disease resistance, nutrients apparent digestibility, intestinal tissue structure, intestinal microflora, prophenoloxidase(pro PO) and trypsin(TRS) m RNA relative expression in hepatopancreas of L. vannamei, to provide a theoretical basis for rational application of protease, organic acid salt and protease-organic acid salt combination in feed and efficient research of shrimp feed.According to the experimental design, 1120 healthy white shrimps(initial body weight 0.33±0.02g) were randomly divided into 7 treatments, 4 replicates per treatment, 40 white shrimps each group(group number are H、L、125P、150P、175P、OA、P+OA). H group was fed high fish meal feed(20% fish meal and 37% crude protein), L group was fed with low fish meal feed(10% fish meal and 37% crude protein), 125 p, 150 P, 175 P, OA, P+OA were fed diets containing 125 mg/kg, 150 mg/kg, 175 mg/kg protease, 325mg/kg organic acid salt and 175mg/ kg protease +325mg/kg organic acid salt, respectively, the experimental period was 9 weeks.The results of growth performance show that: adding protease, organic acid salt and their compound in L group feed could significantly improve weight gain rate(WGR), protein efficiency ratio(PER), specific growth rate(SGR) and significantly reduce the feed conversion ratio(FCR) of shrimp(P<0.05). and in P+OA group was found the optimum value, the survival rate(SR) of P+OA group was significantly higher than that in L group; there were no significant differences in whole body crude protein, crude fat, dry matter, crude ash contents among treatments(P>0.05).The result of immune indexes showed that: with increasing dietary protease level in L group, the activities of alkaline phospharase(AKP) and acid phosphatase(ACP) in serum were increased and then decreased and significantly higher than those of LF(P<0.05), the maximum value of them were found in 150 P, the activities of total superoxide dismutase(T-SOD) and polyphenol oxidase(PO) in serum were significantly improved(P<0.05), the content of malondialdehyde(MDA) in serum was significantly decreased(P<0.05); and the avtivities of AKP, ACP and T-SOD of hepatopancreas in 175 P group were significantly increased(P<0.05). Adding organic acid salt in L group feed could significantly increased AKP、ACP and PO activities and significantly decreased the content of MDA(P<0.05), but there was no significant differences in T-SOD activity; and the avtivities of ACP and T-SOD in hepatopancreas were significantly increased(P<0.05), there was no significant effect on AKP activity(P>0.05). Adding their compound in L group feed could significantly increase AKP、ACP 、T-SOD and PO activities(P<0.05) and significantly decreased the content of MDA(P<0.05), and the activities of AKP, ACP and T-SOD in hepatopancreas were significantly increased(P<0.05).The results of digestive enzymes in hepatopancreas showed that: compared with L group, adding protease could significantly increase trypsin(TRS), lipase(LPS) and amylase(AMS) activities(P<0.05), and 175 P is the highest; adding organic acid salt could significantly increase the activities of TRS and LPS, there was no significant influence on AMS activity(P>0.05); the activities of TRS, LPS and AMS were significantly increased when adding their compound(P<0.05).The results of the challenge test showed that: The 96 h cumulative mortality of 175 P and P+OA when challenged with Vibrio parahaemolyticus significantly lower than that of LF(P<0.05), and the other groups also decreased but there were no significant differences among those groups(P>0.05).The results of nutrients AD showed that: adding protease, organic acid salt and their compound in L group feed could significantly increase the AD of dry matter, crude protein, crude fat and gross phosphorus(P<0.05), but there was no significant effect on the AD of gross energy(P>0.05). As to AD of amino acids, the AD of Leu increased significantly(P<0.05), but there were no significant effects on the AD of other amino acids(P>0.05).The results of intestinal tissue structure and intestinal microflora show that: adding protease, organic acid salt and their compound in L group feed could significantly raise the intestinal villus height of shrimp(P<0.05), P+OA group was the highest, significant effects was found among 150 P, 175 P and P+OA groups(P<0.05), and the supplementation of protease, organic acid salt and their compound could make the intestinal villus more neat and compact. The Shannon index of 175 P and OA grouops greater than L group, The Simpson index of 125 P, 175 P, OA and P+OA less than L group, the contents of Vibrio genera in intestinal microflora of all group less than L group.The results of pro PO and TRS m RNA relative expressions show that: adding protease, organic acid salt and their compound in L group feed could significantly increase the m RNA relative expressions of pro PO and TRS of shrimp(P<0.05), the m RNA relative expressions of pro PO and trypsin were not significantly different between the group of 175 P and P+OA(P>0.05), and significantly higher than those of the other groups(P<0.05).Compared with the H group, the cultivation effect of shrimp fed diets with protease, organic acid salt and their compound were close to that of H group.In summary, under the condition of this experiment, adding protease, organic acid salt and their compound in the diets with plant protein instead of fish meal could promote the growth of L. vannamei, improve the immunity and digestive enzymes activities of hepatopancreas, ameliorate the intestinal tissue structure, reduce the contents of Vibrio genera in intestinal microflora, improve the pro PO and TRS m RNA relative expressions, and the compound group had the best effect. |
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