| An 8-week feeding trial was conducted to evaluate the effects of dietary methionine or methionyl-methionine levels on the growth performance,body composition,serum and hepatic biochemical indexes,IGF-I and IGF-IR gene expression in juvenile bullfrog Rana(Lithobates)catesbeiana with the initial weight of 40.01±0.24 g.Nine isonitrogenous(40% crude protein)and isolipidic(6% crude lipid)diets were formulated with the graded methionine levels(0,0.4%,0.8%,1.2%,1.6% and 2.0%)and methionyl-methionine levels(0.4%,1.2% and 2.0%).The determined methionine levels were 0.63%,1.00%,1.42%,1.78%,2.26%,2.68%,1.00%,1.85%and 2.72% and then defined as Met 0,Met 0.4,Met 0.8,Met 1.2,Met 1.6,Met 2.0,Met-Met 0.4,Met-Met 1.2 and Met-Met 2.0.Fourteen bullfrogs were put into each tank and each treatment had triplicate tanks.All the experimental bullfrogs were fed twice(09:00 and 18:00)to apparent satiation daily.Results of the present study were presented as follows:1.Effects of dietary methionine or methionyl-methionine levels on the growth performance,body composition,serum and hepatic biochemical indexes of bullfrog.During this trial,survival of bullfrog fed diets with methionine or methionyl-methionine was 83.33-95.24% and showed no significant difference(P>0.05).In methionine groups,the weight gain rate(WGR),protein efficiency ratio(PER)and protein productive value(PPV)of Met 0.8 and Met 1.2 were significantly higher than Met 0 and Met 2.0(P<0.05).While no significantly differences were found on survival rate(SR)and feed intake(FI)(P>0.05).In methionyl-methionine groups,There were no significantly differences on WGR,PER,PPV,feed conversion ratio(FCR)and FI(P>0.05).Under the same methionine levels,Met 0.4 and Met-Met 0.4,Met 1.2 and Met-Met 1.2 had no significantly difference on WGR,PER,PPV,FCR and FI(P>0.05).The WGR and PER of Met-Met 2.0 were significantly higher than those of Met 2.0(P<0.05),while no significantly differences were found on FCR,FI,SR and PPV(P>0.05).There were no significantly differences on moisture,crude protein and ash of body and muscle(P>0.05),so it is with the content of crude ash of leg and vertebrae.In methionine groups,the crude lipid of whole body of Met 2.0 was significantly lower than that of the other groups(P<0.05),and the crude lipid of muscle of Met 0.8 was significantly higher than Met 0.4 and Met2.0(P<0.05).In methionyl-methionine groups,there were no significantly differences on crudelipid of body and muscle(P>0.05).Under the same methionine levels,Met 1.2 and Met-Met 1.2,Met 2.0 and Met-Met 2.0 had no significantly difference on crude lipid of whole body and muscle(P>0.05),while the crude lipid of whole body of Met 0.4 was significantly higher than that of Met-Met 0.4(P<0.05).No significantly difference was found on serum triglyceride(TG)among groups(P>0.05).In methionine groups,the levels of serum total cholesterol(T-CHO)of the Met 1.2 was significantly lower than that of Met 0(P<0.05).The levels of serum glucose(GLU)of the Met 2.0 was significantly higher than that of the Met 0.8 and Met 1.2(P<0.05).The levels of serum glutamic oxaloacetic transaminase(GOT)of the Met 0.8 and Met 1.2 were significantly lower than the other groups(P<0.05).The levels of serum alanine aminotransferase(GPT)of the Met 0.8 and Met 1.2 were significantly lower than Met 0(P<0.05),or higher than Met 2.0(P<0.05).In methionyl-methionine groups,no significantly difference was found on TG,T-CHO,GLU and GPT(P>0.05),while the levels of serum GOT of the Met-Met 2.0 was significantly lower than Met-Met 0.4 and Met-Met 1.2(P<0.05).Under the same methionine levels,the levels of serum GOT and GPT of the Met-Met 0.4 was significantly lower than Met0.4(P<0.05),while no significantly difference was found on TG,T-CHO and GLU(P>0.05).No significantly difference was found on TG,T-CHO,GLU,GOT and GPT between Met 1.2 and Met-Met 1.2(P>0.05).The levels of serum GLU and GPT of the Met 2.0 was significantly lower than Met-Met 2.0(P<0.05),while no significantly difference was found on TG,T-CHO and GOT(P>0.05).There were no significantly differences on superoxide dismutase(SOD),methane dicarboxylic aldehyde(MDA),catalase(CAT),GOT and GPT among all the groups(P>0.05).Quadratic regression analysis of the WGR corresponding to the level of dietary methionine indicated that the optimal concentration of dietary methionine for the growth of juvenile bullfrogs was 1.51% of dry diet in the presence of 0.26% cystine(corresponding to 3.77% of dietary protein on a dry weight basis).2.Effects of dietary methionine or methionyl-methionine levels on the IGF-I and IGF-IR gene expression of bullfrog.In methionine groups,no significantly differences were found on the expression of IGF-I and IGF-IR of Met 0.4,Met 0.8 and Met 1.2(P>0.05),while they were significantly higher than Met 0 and Met 2.0(P<0.05).In methionyl-methionine groups,there were no significantly differences on the expression of IGF-I and IGF-IR among the groups(P>0.05).In methionyl-methionine groups,there were no significantly differences on the expression of IGF-I and IGF-IR among all the groups(P>0.05).Under the same methionine levels,no significantly differences were found on the expression of IGF-I of Met 0.4 and Met-Met 0.4,Met 1.2 and Met-Met 1.2(P>0.05),while Met-Met 2.0 had significantly higher of the expression of IGF-Ithan the Met 2.0(P<0.05).The expression of IGF-IR of Met 0.4 or Met 1.2 was significantly higher than that of Met-Met 0.4 or Met-Met 1.2(P<0.05),while no significantly differences were found on the expression of IGF-IR between Met 2.0 and Met-Met 2.0(P>0.05). |
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