| In order to evaluate nutritional and functional effects of yeast-derived feed additive on fish,the study took allogynogenetic silver crucian carp(Carassius auratus gihelio ♀× Cyprints carpio ♂)as the research object,and carried out pond culture experiments in fixed net cages and virulence tests with Cyprinid herpesvirus 2(CyHV-2)infection of allogenic silver crucian carp.The aim of the experiments is to study the effects of yeast hydrolysate,yeast cell wall,yeast extract and yeast nucleotide on growth,health,disease resistance for allogynogenetic silver crucian carp,and the repair effect of yeast hydrolysate on oxidized oil-induced injury of allogynogenetic silver crucian carp.The main results of this paper are as follows:Experiment one:Effect of yeast hydrolysate on growth,health and disease resistance of allogynogenetic silver crucian carpIn order to explore the effect of yeast hydrolysate on growth,health and disease resistance for allogynogenetic silver crucian carp,the experiment selected allogynogenetic silver crucian carp with an average initial body weight of(68.60±0.20)g and randomly divided them into five groups,each with four replicates and 40 fish per replicate.Five groups of experimental fish were fed with basic diet(S),0.2%.0.4%.0.6%molasses yeast hydrolysate and 0.6%beer yeast hydrolysate,respectively prepared the experimental diets of MY1,MY2,MY3 and BY.The fish were cultured in cages for 70 days.The results showed that:1.Compared with group S,MY1 and MY2 had no significant effect on survival rate(SR),specific growth rate(SGR),feed conversion ratio(FCR),fat retention rate(FRR)and protein retention rate(PRR)(P>0.05).SGR of MY3 and BY increased 13.73%和 14.71%(P<0.05),and FCR decreased 14.37%和 15.57%(P<0.05),and had no significant effect on SR,FRR and PRR(P>0.05).2.Compared with group S,the contents of total protein(TP),total bile acid(TBA)and low-density lipoprotein(LDL)in serum of each experimental group increased,but the difference was not significant(P>0.05);the contents of cholesterol(TC),triglyceride(TG),high-density lipoprotein(HDL)and blood glucose(GLU)in each experimental group decreased,but the difference was not significant(P>0.05).3.Compared with group S,there was no significant difference in AST and ALT between groups MY1,MY2,MY 3 and BY(P>0.05).4.Compared with group S,there was no significant difference in ST(P>0.05);FI and FH of MY1 and MY2 had no significant difference(P>0.05),FI of MY3 and BY decreased significantly(P<0.05),and FH increased significantly(P<0.05).5.Compared with group S,serum immunoglobulin(Ig)content and lysozyme(Lzm)activity in MY1,MY2,MY3 and BY groups were significantly increased(P<0.05).With the increase of yeast addition,Ig and Lzm showed an upward trend.There was no significant difference in Ig(P>0.05).Lzm in MY3 was significantly higher than that in MY1 and MY2 group(P<0.05).After injecting CyHV-2 virus solution from visceral tissue fluid of infected fish compared with the control group,the cumulative mortality rate of each experimental group decreased,and the relative percent survival increased.The cumulative mortality rate of MY3 group was the lowest of 5%,and the relative percent survival was the highest of 88.9%.With the increase of molasses yeast hydrolysate,the cumulative mortality rate of allogynogenetic silver crucian carp decreased gradually,and the relative percent survival increased gradually.The results indicated that the growth performance,immunity and disease resistance of allogynogenetic silver crucian carp were improved gradually with the increase of yeast hydrolysate when the contents of molasses yeast hydrolysate was 0-0.6%,and the best performance was obtained with 0.6%yeast hydrolysate.The effects of 0.6%beer yeast hydrolysate and 0.6%molasses yeast hydrolysate on growth performance,liver and intestinal structure,immunity and disease resistance of allogynogenetic silver crucian carp were not significantly different.The two types of yeast hydrolysate could be substituted for each other at 0.6%gradient.Experiment two:Repairing effect of yeast hydrolysate on oxidized oil damage of allogynogenetic silver crucian carpIn order to explore the repaire effect of yeast hydrolysate on oxidized oil-induced injury for allogynogenetic silver crucian carp.the allogynogenetic silver crucian carp with an average initial body weight of(68.60±0.20)g were selected and randomly divided into five groups.each group was set up with 3 replicates and 40 fish per replicate.Five groups of experimental fish were fed with basic diet(S),oxidized soybean oil diet(O).and OMY1,OMY2 and OMY3 experimental diets prepared by adding 0.2%,0.4%and 0.6%molasses yeast hydrolysate to oxidized soybean oil diet respectively.The fish were cultured with cages in ponds for 70 days.The results showed that:1.Compared with group S,PRR and FRR in group O decreased significantly(P<0.05),SGR decreased 16.67%(P<0.05)and FCR increased 26.35%(P<0.05).Compared with O group,SGR of OMY1,OMY2 and OMY3 increased 6.50%、12.55%and 19.51%(P<0.05),FCR decreased 9.95%、19.90%and 22.75%(P<0.05).2.Compared with group S,ALT and AST activities in group O were significantly increased(P<0.05),while AST and ALT activities in group O were significantly decreased by OMY1,OMY2 and OMY3(P<0.05).Compared with group S,the hepatocytes in group O were disorderly arranged,the marginal hepatocyte of central venous area were exfoliated,and cytoplasmic vacuoles were observed.The hepatocytes in group O were smaller and the boundary between cells was blurred.There was no significant difference in hepatocyte structure between OMY1,OMY2,OMY3 and S groups,and the cell boundaries are obvious,arranged neatly.3.There was no significant difference in FI among the experimental groups(P>0.05).Compared with group S,ST increased significantly in group O(P<0.05)and FH decreased significantly(P<0.05).Compared with group O,OMY1,OMY2 and OMY3 could significantly reduce ST(P<0.05).Compared with group O,OMY1,OMY2 and OMY3 significantly increased FH(P<0.05).4.Compared with group S,the content of MDA in group O increased significantly(P<0.05),while OMY1,OMY2 and OMY3 decreased significantly(P<0.05),and there was no significant difference between group O and group S(P>0.05).Compared with group S,GR,GPx and GST activities in group O were significantly increased(P<0.05),while OMY1,OMY2 and OMY3 significantly decreased the activities of these three enzymes(P<0.05),and there was no significant difference between group O and group S(P>0.05).Compared with group S,the content of GSH in group O decreased significantly(P<0.05),while OMY1,OMY2 and OMY3 increased the content of GSH significantly(P<0.05).Compared with group S,the relative expression of GCLC mRNA in group O was significantly down-regulated(P<0.05),while the expression of GR,GPx and GST-ω mRNA were significantly up-regulated(P<0.05).Compared with group O,the relative expression of GCLC mRNA in OMY1,OMY2 and OMY3 groups significantly up-regulated(P<0.05),and GR,GPx and GST-ω mRNA were significantly down-regulated in OMY1,OMY2 and OMY3 groups(P<0.05),but there was no significant difference between OMY1,OMY2,OMY3 and S groups(P>0.05).The results indicated that dietary oxidized oil can cause the injury of glutathione antioxidant system,severe hepatopancreas and intestinal damage,resulting in a significant decrease in growth performance of allogynogenetic silver crucian carp.On this basis,0.2%,0.4%and 0.6%molasses yeast hydrolysate were added,which can repair glutathione antioxidant system,repair liver and intestinal damage caused by oxidized oil,thus improving the growth performance of allogynogenetic silver crucian carp.Experiment three:Effects of yeast cell wall,yeast nucleotide and yeast extract on growth,health and disease resistance of allogynogenetic silver crucian carpIn order to explore the effect of yeast nucleotide,yeast extract and yeast cell wall on growth.health and disease resistance for allogynogenetic silver crucian carp,the experiment selected allogynogenetic silver crucian carp with an average initial body weight of(7.64±0.04)g and randomly divided them into five groups.Each group had four replicates with 40 fish per replicate.Five groups of experimental fish were fed with basic diet(C)and experimental diets supplemented with 0.6%yeast nucleotide YT500(YN5).0.6%yeast nucleotide YT1000(YN10),0.4%yeast extract(YE)and 0.2%yeast cell wall(YC)respectively.The fish were cultured in cages for 72 days.The results showed that:1.YN5.YN10.YE and YC had no significant effect on SGR,FCR,FRR and PRR of allogynogenetic silver crucian carp compared with group C(P>0.05).2.Compared with group C.YN5.YNN10.YE and YC had no significant difference in serum TBA.TC.TG.HDL,LDL.TP and GLU(P>0.05).The results showed that YN5,YN10,YE and YC had no significant effect on blood sugar and lipid metabolism of allogynogenetic silver crucian carp.3.Compared with group C,YN5,YN10,YE and YC had no significant effect on serum AST and ALT(P>0.05).indicating that the addition of YN5,YN10,YE and YC did not damage the liver permeability of allogynogenetic silver crucian carp and could maintain liver health.4.Compared with group C,YN5,YN10,YE and YC had no significant effect on the ST,FI and FH(P>0.05),and could maintain the intestinal health.5.Compared with group C.Lzm activity and Ig content of YC group had no significant difference(P>0.05),Lzm activity and Ig content of YN5,YN10 and YC were significantly increased(P<0.05),and Lzm activity and Ig content of YN10 were significantly higher than those of YN5 and YC(P<0.05).Compared with group C,the cumulative mortality rate and relative percent survival of YE group did not change after injecting CyHV-2 virus solution from visceral tissue fluid of infected fish,.The cumulative mortality rate of other experimental groups decreased and the relative percent survival increased.The cumulative mortality rate of YN10 group was the lowest of 8.9%and the relative percent survival was the highest of 69.2%.The results indicated that 0.6%yeast nucleotides YT500 and YT1000.0.4%yeast extracts and 0.2%yeast cell wall could not damage growth and health of allogynogenetic silver crucian carp.0.6%yeast nucleotides YT500 and YT1000,and 0.2%yeast cell wall could improve the immune performance of the body and thus enhance the resistance of allogynogenetic silver crucian carp to CyHV-2,of which 0.6%yeast nucleotides YT1000 was the best. |
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