Effects Of L-carnitine On Production Performance,Ammonia Excretion Rate And Resistance To Acute Low Temperature Stress Of Cyprinus Carpio

In order to explore the effect of L-carnitine on the production performance,ammonia excretion rate and cold stress resistance of Cyprinus carpio and its mechanism.A total of270(about 130 g)healthy Cyprinus carpio were randomly allotted into 3 groups.They were fed with control diet(basic diets of Cyprinus carpio),high fat diet(protein decreased by 6% and fat increased by 5% on the basis of control diet)and High fat L-carnitine diet(500 mg/kg L-carnitine was added on the basis of high fat diet)respectively.After 8 weeks of feeding,growth performance,meat quality,plasma biochemical and antioxidant capacity were evaluated.The concentration of ammonia nitrogen in the water of Cyprinus carpio was continuously measured by Nessler’s colorimetry within 8 hours after satiety,so as to obtain the change rule of ammonia excretion rate of Cyprinus carpio in each group.The swimming ability,blood sugar concentration and plasma cortisol concentration of Cyprinus carpio under acute cold stress for 6 h and 12 h were observed by animal behavior instrument,and the effect of L-carnitine on the ability of resist acute cold stress was monitored.And its mechanism was explored by RNA SEQ sequencing technology and bioinformatics analysis.The results shows:(1)Compared with the high-fat group,the FBW of High-fat L-carnitine group markedly increased(P<0.05);the ILI of High-fat L-carnitine group was dramatically higher than that of other two groups(P<0.05);Meanwhile total cholesterol value of High-fat L-carnitine group was significantly lower than that of the high-fat group(P<0.05);Compared with the control group,the urea nitrogen content of the High-fat L-carnitine group and high-fat group decreased notably(P<0.05);The T-AOC and the activity of CAT in High-fat L-carnitine group were significantly higher than those of the high-fat group(P<0.05);The content of ash and zinc in the dorsal muscles of the high-fat group and High-fat L-carnitine group were significantly lower than those of the control group(P<0.05);In High-fat L-carnitine group,the content of protein and iron in dorsal muscle were significantly increased,while the content of water was remarkably decreased(P<0.05).(2)The concentration of ammonia nitrogen in the water within 8 hours after Cyprinus carpio satiety was measured.It was found that the ammonia excretion rate of the three groups basically declined after an increase.the ammonia excretion rate peak of the control group and the high-fat group emerged at the second hour,and that of the High-fat L-carnitine group appeared at the first hour.Generally,the ammonia excretion rate of the control group was the highest,followed by the high-fat group,and the High-fat L-carnitine group was the lowest.(3)Within 0.5h of acute cold stress,the Cyprinus carpio in High-fat L-carnitine group had the longest exercise distance,the second was high-fat group,and the shortest was control group;the Cyprinus carpio in control group had 52.23% time of rest,while high-fat group and High-fat L-carnitine group had only 18.47% and 14.08% time of rest,respectively.After cold stimulation,the concentration of serum cortisol in High-fat L-carnitine group at 6 h and 12 h were lower than those in the control group and high-fat group,while the concentration of blood sugar was higher than those in the other two groups,but didn’t reach significant level(P>0.05).(4)Compared with the control group,1499 genes were up-regulated and 1155 genes were down-regulated in the high-fat group,while 2823 genes were up-regulated and 2325 genes were down-regulated in the High-fat L-carnitine group.Compared with the high-fat group,2107 genes were up-regulated and 1936 genes were down-regulated in High-fat L-carnitine group.The genes of cpt1 and cpt2 related to lipid β oxidation and m TOR related to protein synthesis in hepatopancreas were up-regulated,while the genes of fasn and elovl6 related to lipogenesis and elongation were down-regulated.To sum up,dietary 500 mg/kg L-carnitine supplementation could alleviate the negative effects of high-fat diet on the growth performance of Cyprinus carpio.It can reduce cholesterol content in plasma,increase protein deposition in dorsal muscle,reduce ammonia nitrogen emission,and enhance the ability of fish to resist cold stress and antioxidation.The specific molecular mechanism of L-carnitine promoting growth,reducing lipid and increasing nitrogen reserve are as follows: L-carnitine increased the lipolysis ability of Cyprinus carpio by up-regulating the expression of cpt1 and cpt2;The down-regulated expression of fasn、elovl6 limited lipid production and elongation,so as to reduce the accumulation of lipid in Cyprinus carpio;The up-regulated expression of mtor in live promoted the synthesis of protein.