Genetic Parameters Estimate Of Meat Color Traits And The Transcriptomic Analysis Of The Effect Of Special Feeds On Meat Color In Hu Sheep

Among the assessment indexes of meat quality,meat color is the embodiment of physiological,biochemical and microbiological characteristics of meat at the appearance level.As an important index to evaluate the appearance of meat,meat color always affects consumers’first impression and feeling of meat.Therefore,meat color is an important index for meat quality assessment.In the work of sheep genetic breeding,the research on meat color traits is beneficial to meet the consumers demands and production needs.In this study,Hu sheep was selected as the research object.Based on the data of meat color,pedigree information and genomic information of 1955 Hu sheep,the ASReml software and REML method were used to estimate the variance components,and then calculate the heritability,genetic correlation and phenotypic correlation.Meanwhile,on the basis of the obtained meat color data,the meat color grading cards corresponding to 45 min and 24 h postmortem were established according toΔE.In addition,the effects of replacing part of corn straw with liquorice or fennel in the diet on meat color traits of Hu sheep were explored.Transcriptomic sequencing analysis was used to identify the key genes of the effect of dietary factors on meat color traits.The main findings of this study were as follows:（1）The genetic parameters of meat color traits were estimated based on the pedigree and genomic information in 1955 Hu sheep.Results showed that L*_45min,L*_24h,a*_24h and b*_24h are in medium or high heritability with the range of 0.21～0.46,while a*_45min and b*_45min were in low heritability with the range of 0.01～0.18.All traits of meat color showed positive genetic and phenotypic correlations to varying degrees.Among them,the genetic correlation value between L*_45min and a*_45min,b*_45min,L*_24h was 0.83±0.58,0.98±0.48,0.93±0.70,respectively.,and the genetic correlation value between b*_24h and L*_24h,a*_24h was 0.94±0.44,0.91±0.07,respectively.（2）According to the results of correlation analysis between the measured values（L*,a*,b*）,calculated values（ΔE,C,Hue）and subjective scores of 392 individuals from the above population,ΔE had the largest correlation coefficient with subjective scores and was selected as the grading index.The meat color of 1955 Hu sheep longissimus dorsi were divided into six grades according toΔE.After verification and adjusting,a color grading card was established for subjective evaluation of meat color at 45 min and 24 h postmortem.（3）Replacing part of the corn straw in the pellet total mixed ration with liquorice or fennel in the diet caused a decrease in the L*_24h,a*_24h and b*_24h values and Gumminess,Chewiness in Hu sheep,and increase the cooked meat rate and Springiness.In addition,the m RNA expression levels of My HCIIa and My HCIIx significantly increased（P﹤0.001）in the longissimus dorsi of Hu sheep from liquorice group.The m RNA expression levels of My HCIIa,My HCIIx and My HCIIb significantly increased（P﹤0.001）in fennel group.And in both two experimental groups,the m RNA expression level of My HCI showed a decreasing tendency（P=0.053）.These changes on the expression levels of different My HC subtypes indicated that there was a tendency of transform from I to II in muscle fiber types of the experimental groups,which could lead to the changes of meat color.Based on the significant differences of meat color between the experimental groups and the control group,6 individuals were selected for transcriptomic sequencing in each group.Two key modules related to a*_24h and b*_24h were identified based on WGCNA method（r=0.63～0.78,P<0.01）.A total of 7 key genes related to meat color were identified by KEGG analysis,among which SMURF1,DDB2,CUL2,NEDD4L and TRAF6 were enriched in ubiquitin mediated proteolysis pathway,belonging to ubiquitin ligase E3.NOS3 and PLCG2 enriched in calcium signaling pathway may be related to the transformation of muscle fiber types.In this study,we obtained the genetic parameters of meat color traits,established the meat color grading cards could be used at 45 min and 24 h postmortem,and identified the key genes corresponding to the effect of special feeds on meat color.This study provides scientific basis and technical support for genetic improvement and nutritional regulation of meat color traits.