蛋氨酸二肽在幼鲤饲料中的有效性研究及幼鲤蛋氨酸需求量的再评估

Effectiveness of Methionine Dipeptide in Juvenile Common Carp Diet and Methionine Requirement of Juvenile Common Carp Re-Evaluated by Methionine Dipeptide

本试验通过在低蛋氨酸(Met)饲料中添加不同水平的蛋氨酸二肽(Met-Met),评价Met-Met在幼鲤饲料中的有效性并确定幼鲤的Met需求量。试验用幼鲤初始体重为(16.7±0.08)g,随机分为7组,每组6个重复,每桶30尾鱼。在以豌豆浓缩蛋白作为蛋白质源的低Met基础饲料[Met含量为4.8g/kg,半胱氨酸(Cys)含量为4.4g/kg]中分别添加0、1.5、2.0、2.5、3.0、4.0g/kg的Met-Met,饲喂6组试验鱼,分别命名为M0、M1.5、M2、M2.5、M3、M4组;剩余的1组试验鱼饲喂含10%鱼粉同时补充3.0g/kg晶体DL-Met的试验饲料,命名为FM组,作为正对照组。饲养试验持续10周。结果显示:与M0组相比,各Met-Met添加组幼鲤的末均重、增重率、特定生长率均显著增加(P<0.05),而饲料系数均显著降低(P<0.05)。分别以增重率、饲料系数为评价指标,通过一元二次回归模型分析获得幼鲤Met需求量分别为8.1、7.9g/kg;以蛋白质沉积率为评价指标,通过折线模型分析获得幼鲤Met需求量为7.6g/kg。饲料中添加不同水平Met-Met均可显著增加全鱼中Met、Met+Cys、赖氨酸(Lys)、色氨酸(Trp)、异亮氨酸(Ile)、亮氨酸(Leu)、缬氨酸(Val)、组氨酸(His)的含量(P<0.05),而各Met-Met添加组与FM组之间均没有显著差异(P>0.05)。M0组幼鲤必需氨基酸沉积率显著低于其余各组(P<0.05);M0、M1.5、M2、M2.5组的Met沉积率显著高于FM组(P<0.05);除M1.5组外,各Met-Met添加组的Lys沉积率均显著高于M0组(P<0.05),且各Met-Met添加组与FM组之间差异不显著(P>0.05)。M4组血浆高密度脂蛋白胆固醇(HDL-C)/总胆固醇(TC)显著高于FM和M0组(P<0.05)。M2、M4组血浆总抗氧化能力(T-AOC)显著高于M0组(P<0.05)。血浆丙二醛(MDA)含量以M3组最低,显著低于除M1.5、M4组外的其余各组(P<0.05)。由此得出,在Met缺乏的基础饲料(含4.8g/kgMet)中添加适量Met-Met可有效促进幼鲤摄食和生长,促进脂肪的转运与代谢,提高抗氧化能力。基于增重率、饲料系数和蛋白质沉积率的回归分析,获得幼鲤Met需求量为7.6~8.1g/kg(饲料中Met-Met添加量为2.95~3.47g/kg),占饲料蛋白质的2.0%~2.1%。饲料中Met-Met所提供的Met与天然蛋白质源中Met在消化吸收与利用上特性相似,以Met-Met为来源评估幼鲤Met需求量会更加准确。

This experiment was aim to evaluate the effectiveness of methionine dipeptide (Met-Met) in juvenile common carp diet and to determine the methionine (Met) requirement of juvenile common carp ( Cyprinus carpio ) by adding different levels of Met-Met into the diet.Juvenile common carp with the body weight of (16.70±0.08) g randomly assigned to 7 groups with 6 replicates per group and 30 juvenile fish per replicate.Using pea concentrated protein as protein source,six experimental diets supplemented with 0,1.5,2.0,2.5,3.0 and 4.0 g/kg Met-Met were prepared based on a low Met diets with 4.8 g/kg Met and 4.4 g/kg cysteine (Cys) to fed fish in 6 groups,which was named as M0,M1.5,M2,M2.5,M3 and M4 groups,respectively.Fish in the last group were fed a diet contained 10% fish meal and supplemented with 3.0 g/kg crystal DL -Met ,which was named as FM group (positive control group).The feeding trial lasted for 10 weeks.The results showed as follows: compared with M0 group,the final average body weight,weight gain rate (WGR) and specific growth rate (SGR) were significantly increased and the feed conversion ratio (FCR) was significantly decreased in each Met-Met group ( P <0.05).Taking WGR and FCR as assessment indexes,the Met requirements of juvenile common carp were 8.1 and 7.9 g/kg according to monodic quadratic regression model analysis,respectively.Taking protein retention rate (PRR) as assessment index,the Met requirement of juvenile common carp was 7.6 g/kg according to broken-line regression analysis.Diets supplemented with different levels of Met-Met all could significantly increase the contents of Met,Met+Cys,lysine (Lys),tryptophan (Trp),isoleucine (Ile),leucine (Leu),valine (Val) and histidine (His) in whole body,but there were no significant differences between each Met-Met group and FM group ( P >0.05).Essential amino-acid retention rate in M0 group was significantly lower than that in other groups ( P <0.05).Met retention rate showed a decrease trend with the Met-Met supplemental level increasing,and the Met retention rate in M0,M1.5,M2 and M2.5 groups was significantly higher than that in FM group ( P <0.05 ).Lys retention rate in M0 group was significantly lower than that in Met-Met groups except M1.5 group ( P <0.05),and there was no significant difference between each Met-Met group and FM group ( P >0.05).Plasma high density lipoprotein cholesterol (HDL-C)/total cholesterol (TC) in M4 group was significantly higher than that in FM and M0 groups ( P <0.05 ).Plasma total antioxidant capacity (T-AOC) in M2 and M4 groups was significantly higher than that in M0 group ( P <0.05).Plasma malondialdehyde (MDA) content in M3 group was the lowest,which was significantly lower than that in other groups except M1.5 and M4 groups ( P <0.05).In conclusion,suitable level of Met-Met added into a Met deficiency diet with 4.8 g/kg Met can effectively promote the growth and feeding,improve the transport and metabolism of lipid,and increase antioxidant ability of juvenile common carp.Met requirement of juvenile common carp is estimated to be 7.6 to 8.1 g/kg (the supplemental level of Met-Met in the diet is 2.95 to 3.47 g/kg),which account for 2.0% to 2.1% dietary protein,by regression analysis base on WGR,FCR and PRR.The Met supplied by Met-Met has the similar characteristics in digestion,absorption and utilization with the Met from natural protein source.So,it is can be more accurate to evaluate the Met requirement of juvenile common carp using Met-Met.