| This study was conducted to investigate the effects of dietary methionine and lysine levels on carcass performance and meat quality, and circumstance of methylation of genomic DNA and specific MSTN gene in broiler, and the molecular mechanism of dietary amino acids affected growth of broilers were investigated.1. Analysis of carcass performance of 55-day-old broilers fed with different amino acid levels showed that there were significant differences(P <0.05)in the average weight, carcass weight and live weight between the control group and the group A(0.825>0.368,0.740>0.328).Semi-eviscerated yield and eviscerated yield of the control group and the group F were the maximum, whlie semi-eviscerated yield of A group was the minimum in 7 groups; There was no significant (P>0.05)difference in percentage of slaughter yield, percentage of semi-eviscerated yield, and percentage of eviscerated yield between each group.2. High performance liquid chromatography (HPLC) was'used in this study to determinate genome methylation level in muscle and liver tissues of broiler.The results showed the DNA methylation content in muscle and liver tissues of 21,35 or 55-day-old broilers was 34.60% and 37.66%,30.39% and 22.06%, or 17.87 and 16.03% respectively, suggesting that DNA methylation contents in the muscle and liver tissues decreased with the increase of growth time.3. Analysis of the correlation between methylation content and carcass performance in 55-day-old broilers of muscle and liver tissue showed that DNA methylation content in muscle tissue was postively correlated to the live weight and carcass weight at 55 day-old broilers(r= 0.774,0.775), and was negatively correlated to percentage of slaughter yield percentage of semi-eviscerated yield and percentage of eviscerated yield (r=-0.293,-0.464,-0.091). DNA methylation content in liver tissue was postively correlated to the slaughter weight, semi-eviscerated yield and eviscerated yield at 55 day-old broilers(r=0.763,0.768, 0.785), and was negatively correlated to percentage of slaughter yield and percentage of semi-eviscerated yield (r=-0.502,-0.161). 4. Determination of meat quality in each group of 55-day-old broilers, including the dripping water loss, cooked loss rate, tenderness and pH showed that the dripping loss of the groups C and E was significantly higher than that of the control group (the group Z); Muscle shear force of the group A was significantly(P<0.05) higher than the control group (45.09N>22.33N); Cooked meat rate of the group B were significantly higher than the control group; Among seven groups pH value of the control group was the maximum 6.72, were significant difference in comparison to group A and D.5. Methylation level of the first exon of MSTN gene was measured in muscle tiusse of 21,35 and 55-day-old broiler. The results showed that eight and six sites of the control group and the group D were in the state of methylation at 21 day-old broiler, respectively, except for 2446-7bp and 2451-2bp in the group D, while in the group A, only one site (2355-6bp) was methylated;The methylation level of the control group was the highest at 35-day-old,5 of 8 sites were methylated,and methylation rate was 62.5%. Followed by group D, four sites were methylated,and methylation rate was 50%. Group A is only 2456-7bp site methylated, which methylation rate was 12.5%; 8 sites of the control group were methylated at 55-day-old broiler, followed by A group, which five sites were methylated;6. Effects of different levels of amino acids on mRNA expression of MSTN gene was analyzed in 55 day-old broiler. The results showed that the gray value in the group D was significantly higher than that in the groups A, E and F. The mRNA expression level of MSTN gene was negatively correlated to its first exon methylation levels in 55 days old chicken muscle.
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