| The aim of the study was to study the effects of different levels of methionine(Met)concentrations on the muscle synthesis,digestion and absorption ability and antioxidant ability of Songpu mirror carp.In this experiment,fishmeal,soybean meal,cotton meal and rapeseed meal were used as the main protein source to prepare a basic feed with a methionine content of 0.56%(control),DL-Met(0.1%,0.2%,0.3%,0.4%,0.5%)were added separately into the control diet,and the six experimental diets with the Met level were 0.56%,0.66%,0.75%,0.83%,0.92%,1.01%.The experiment lasted for 8 weeks.On the end of the culture experiment,fish was weighed,and fish muscle,intestine,liver and other tissues were dissected for analysis of muscle quality,development of digestive organs,digestion and absorption,and antioxidant enzymes.The results showed that the 0.75% Met group could significantly increase weight gain rate and specific growth rate of carp(P<0.05),the 0.83% Met group could significantly increase condition factor,crude protein content of the muscle,and could significantly reduce feed conversion ratio of carp(P<0.05),using broken-line model based on PER and SGR indicated that optimum Met level in the diet of juvenile Mirror carp was 0.9% of diet(dry matter basis)with cystine level at 0.64%;the content of Met in the diet could increase the p H and Nrf2 m RNA expressions level of the muscle of carp.Furthermore the content of Met in the diet could promote relative expressions of IGF-I,m TOR,stk11 and pik3r3 in the muscle synthesis pathway;Met in the diet could significantly increase the length villous,intestinal crypt of intestine,and the thickness of the base layer of the foregut and midgut;The Met in diet could significantly increase the intestinal trypsin,lipase and amylase activities,AKP and CK activitys of intestine and the ability of digestion and absorption of carp(P<0.05);SOD,CAT the antioxidant ability and GPx activitys in intestine and liver was significantly increased,and the MDA significantly decreased with an increase in dietary Met levels(P<0.05).In summary: the addition of Met in feed can significantly improve the growth performance,improve digestion,absorption and antioxidant ability and muscle quality of the carp,promote relative expression of genes involved in muscle synthesis.Broken-line model of PER and SGR indicated that optimum Met level in the diet of juvenile Mirror carp was 0.9% of diet(dry matter basis)with cystine level at 0.64%. |
