| This paper targets the juvenile crab of Eriocheir sinensis.On the basis of exploring the growth and antioxidant properties of several representative anti-nutritional factors on juvenile crabs,the study focused on how to eliminate the negative effects of phytic acid in feed on E.sinensis by adding phytase.Phytase was added to the feed of different plant protein content.The effect of phytase on the growth,material utilization and antioxidant of juvenile crab was observed.The research results can provide reference for improving the utilization rate of plant protein of E.sinensis and developing high-efficiency and environmentally friendly feed.The main findings and conclusions are as follows:1.Effects of four anti-nutritional factors on growth performance,digestive enzyme activity and antioxidant enzyme activities of E.sinensisAnti-nutritional factors are the main substances that affect the efficient use of plant products in animal bodies.Different anti-nutritional factors in feeds play different roles.In this experiment,four anti-nutritional factors,phytic acid,stachyose,isoflavones and tannins,were selected,and each factor was designed to be added to the feed at two concentrations.Recorded as phytic acid-1(P1),phytic acid-2(P2),stachyose-1(S1),stachyose-2(S2),soy isoflavone-1(I1),soy isoflavone-2(I2),tannin-1(T1)and tannin-2(T2),and a group in which no anti-nutritional factor was used as a control group(C).Juvenile crabs with an initial body weight of(0.33 ± 0.00)g were fed for 8 weeks.The results showed that the survival rate of juvenile crabs in each experimental group ranged from 80.95 % to 90.28 %,and there was no significant difference(P > 0.05).The four anti-nutritional factors reduced the weight gain rate and specific growth rate of juvenile crabs,but there was no significant difference(P > 0.05).Compared with the C group,the addition of four anti-nutritional factors did not affect the water content,crude protein,crude fat and ash content of the Chinese mitten crab(P > 0.05).The activity of trypsin in the hepatopancreas andintestine of the phytic acid-added group was significantly lower than that of the C group(P < 0.05),and the other anti-nutritional factors had no significant effect on the digestive enzyme activities of the hepatopancreas and the intestine(P > 0.05);The activity of SOD in hepatopancreas of juvenile crabs with phytic acid addition group has a certain decreasing trend(P > 0.05).The stachyose addition group did not affect the hepatopancreatic antioxidant properties of juvenile crabs(P > 0.05).The tannin and soy isoflavone addition groups significantly improved the hepatopancreatic antioxidant properties of juvenile crabs(P < 0.05).In summary,the addition of four anti-nutritional factors to the feed did not significantly affect the growth performance of the Chinese mitten crab.The four anti-nutritional factors have different effects on juvenile crabs due to their different characteristics.Among them,the addition of phytic acid in the feed significantly reduced the hepatopancreas and intestinal trypsin activity of the juvenile crab,which had a negative effect on the digestive performance of the juvenile crab.Phytic acid and stachyose had no significant effect on the antioxidant activity of the juvenile crab.Soy isoflavones and tannins significantly increased the activity of antioxidant enzymes in hepatopancreas,suggesting that soy isoflavones and tannins are beneficial in improving the performance of oxidation reaction,its role and reasonable amount of additives deserve further discussion.2.Effects of different doses of phytase on growth,digestibility and material utilization of E.sinensisPhytase is a green additive that can specifically remove the anti-nutritional effect of phytic acid.This experiment aims to explore the effects of different doses of phytase on growth,digestibility and material utilization of E.sinensis.The control feed contained no phytic acid and phytase.In the juvenile crab feed containing 10 g/kg of phytic acid,phytase was added at levels of 0,500,1000,1500,2000 U/kg,respectively,and recorded as groups P0,P500,P1000,P1500 and P2000,respectively.Juvenile crab initial body weight(4.34 ± 0.05)g.Weighed and sampled after 56 daysof feeding.The results showed that phytic acid significantly reduced the weight gain rate,specific growth rate and protein efficiency of the Chinese mitten crab,and the feed coefficient was significantly higher than that of the C group(P < 0.05).With the addition of phytase in the feed,the growth performance gradually increased,and the P2000 group reached the best,and the feed coefficient of this group was the lowest(P< 0.05).The phosphorus content of whole crabs in P1500 and P2000 groups was significantly higher than that in P0(P < 0.05).In P2000,the trypsin and amylase in the hepatopancreas,and the trypsin activity in the intestine of the Chinese mitten crab reached the highest(P < 0.05);The addition of phytase enhanced the digestibility of protein and the dialysis rate of mineral phosphorus in juvenile crabs.P2000 juvenile crabs have the highest nitrogen and phosphorus retention rates(P < 0.05).The above results show that the addition of 2000 U/kg phytase to feed containing phytic acid can significantly increase the growth rate and trypsin activity of juvenile crabs,promote the utilization efficiency of protein in juvenile crabs,and reduce the feed coefficient.In addition,the addition of phytase can also effectively increase the phosphorus content and nitrogen/phosphorus retention rate of the juvenile crabs of E.sinensis,and improve the utilization of mineral nutrients in juvenile crabs.The results of this experiment suggest that phytase can not only improve the utilization of plant protein in juvenile crabs of E.sinensis,but also has important significance in the field of environmental protection,which can reduce the excretion rate of nitrogen and phosphorus in water environment.3.Effects of phytase added in plant protein meal feed on growth,digestive enzyme activity,nitrogen and phosphorus utilization and antioxidant activity of juvenile E.sinensisIn order to study whether the addition of phytase to plant protein feed can eliminate the negative impact of high proportion of vegetable protein feed on E.sinensis,three feed levels of soy protein concentrate(45%,40%,35%)weredesigned and added.Two doses of phytase(0,2000 U/kg)were recorded as 45,45+,40,40+,35,35+,respectively,and the group containing no soy protein concentrate was used as the control group(C).The initial weight of juvenile crab was(0.22 ± 0.00)g.The results after 8 weeks of culture showed that the different content of soy protein concentrate in feed had no significant effect on the survival rate and food intake of Chinese mitten crab(P > 0.05).The weight gain rate and specific growth rate of group C reached the highest,significantly higher than 45 and 40 groups(P < 0.05).There was no significant difference in weight gain rate between the 35+ group and the40+ group in the phytase-added group(P > 0.05),but both were significantly higher than the 45+ group(P < 0.05).The survival rate,weight gain rate,specific growth rate,feed coefficient and body composition of the 40+ group were not significantly different from those of the C group(P > 0.05).The content of soy protein concentrate in feed decreased,and the activity of digestive enzymes increased(P > 0.05).The activity of trypsin in hepatopancreas of group C was significantly higher(P < 0.05).The addition of phytase increases digestive enzyme activity.When phytase was added at 40% soy protein concentrate,the digestive enzyme activities in hepatopancreas and intestine were not significantly different from those in group C(P > 0.05).As the content of soy protein concentrate in the feed decreased and the fish meal content increased(P > 0.05),the phosphorus intake of juvenile crabs gradually increased(P >0.05),and the C group was significantly higher than the other groups(P < 0.05).After the addition of phytase,the retention rate of nitrogen and phosphorus also increased gradually,and the 35+ group was significantly higher than the 45+ group(P < 0.05).There was no difference in the nitrogen and phosphorus intake,excretion and retention rate between the 40+ group and the C group(P > 0.05).As the content of soy protein concentrate in the feed decreased,the MDA content in the hepatopancreas of juvenile crabs decreased,and the C group was significantly lower than the 45groups(P < 0.05).The SOD activity of group C reached the highest level(P < 0.05).After the addition of phytase,the activities of GSH-Px and T-AOC increased,the content of MDA decreased significantly,and the activities of SOD and the content of GSH increased significantly(P < 0.05).Compared with the C group,the SOD activity of the hepatopancreas of the 40+ group was significantly decreased.There was no significant difference in GSH-Px,T-AOC activity and the content of GSH and MDA between the 40+ group and the C group(P > 0.05).On the other hand,when phytase was added at the same soy protein concentrate level,the survival rate,total phosphorus content,trypsin activity in the hepatopancreas and intestine,and intestinal amylase activity in the 45+ group were significantly higher than those in the 45group(P < 0.05).The trypsin activity in the 40+ group hepatopancreas was significantly higher than that in the 40 group(P < 0.05).The feed coefficient and malondialdehyde content of the 35+ group were significantly lower than that of the 35 groups,and the SOD activity is significantly higher than 35 groups(P < 0.05).In summary,when the level of soy protein concentrate added in the feed is below 40%,the addition of phytase can increase the digestive enzyme activity in the digestive tract of the juvenile crab and improve the utilization of plant materials,thereby promoting the growth of the juvenile crab.The rate and utilization rate of nitrogen and phosphorus in the feed were obtained at levels comparable to those of the control group.Therefore,when considering the content of soy protein concentrate in the feed is 40%,the reasonable addition of phytase 2000U/kg can achieve good feeding effect,which can not only improve the growth performance,digestive performance and antioxidant performance of E.sinensis.It is also beneficial for Chinese mitten crabs to rationally utilize plant protein sources,reduce the waste of mineral elements,and protect the environment. |
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