| The distribution and deposition of fat in meat animals are the key factors affecting carcass quality and meat flavor,and subcutaneous fat and abdominal fat affect carcass quality,and intramuscular fat is the material basis for the formation of marbling,directly involved in the formation of meat tenderness,juiciness and meat flavor.At present,high-fat sheep breeds are gradually being eliminated or improved by hybridization worldwide,and some fat-tail(breech)breeds that are resistant to crude feeding,disease resistance and with strong adaptability are on the verge of extinction.Directional improvement and gene protection are conducted for high-fat sheep breeds which are directed to regulate the distribution of body fat while retaining their excellent disease resistance and adaptive properties.On the premise of ensuring economic benefit,it can effectively increase the content of intramuscular fat,reduce the content of subcutaneous fat and visceral fat,improve the quality of carcass and the flavor of meat.The production of high-quality meat to meet the requirements of people?s living standards has become a major problem to be solved in sheep breeding and production practice.In this study,the local breeds of fine sheep with great differences in body fat distribution in West China(Gansu)were taken as the object of study,and the biological characteristics of Lanzhou fat-tailed sheep(LFTS),small-tailed han sheep(STHS),and Tibetan sheep(TS),three different fat-tailed sheep breeds,were systematically studied,which combines slaughter performance,meat performance,body fat distribution,fatty acid composition,histomorphological analysis and others;High-throughput sequencing of miRNA was performed on adipose tissue of different parts of LFTS and STHS to screen differentially expressed miRNA,and the target gene prediction and functional annotation analysis of differentially expressed miRNA,were carried out to clarify its role in regulating the growth and development of adipocytes;Potential Indel loci of SIRT7 gene related to body fat distribution was detected in two representative Mongolian wool and meet purposed breeds and five Chinese local sheep breeds.The association between SIRT7 gene and growth traits of sheep was discussed.The following results were obtained:1.Comparative study on production performance,slaughter performance and meat quality of sheep with different fat-tail typesIn order to study the differences of production performance,slaughter performance,organ development and meat quality of different fat-tail sheep,every six 8-month-old wethers of LFTS,STHS and TS breeds were selected under the same feeding and management level.The slaughter test was conducted after production performance was measured.The correlation between production performance and slaughter performance was analyzed.The results showed that:(1)Production Performance: the body length and height of LFTS were significantly higher than those of STHS and TS(P<0.05).The chest circumference,chest depth and rump width of LFTS and TS were significantly higher than those of STHS.(2)Slaughter Performance: the pre-slaughter live-weight of LFTS was 48.14% and 24.27% higher than that of TS and STHS(P<0.05),and the carcass weight and bone weight were LFTS>TS>STHS.And the dressing percentage and net meat weight of LFTS and TS were significantly higher than that of STHS(P<0.05).(3)Organ Development: The heart index of LFTS was significantly higher than that of TS(P<0.05),and the liver index: STHS>TS>LFTS(P<0.05),and the small intestine index of STHS,the tail fat index of LFTS and the perirenal and omentum fat index of TS were the highest among the three breeds,and the index was significantly higher than the other indexes of two breeds(P<0.05).(4)Meat Quality: the shearing force of STHS was 0.30±0.12 kgf,significantly lower than that of LFTS and TS(P<0.05),and there was no significant difference in other meat quality indexes among the three breeds.Conclusion: At the same level of feeding,the comprehensive performance of production and slaughter of three breeds was as follows: LFTS>TS>STHS;The tail-fat weight index of LFTS was significantly higher than that of TS and STHS,fully reflecting the breed characteristics.STHS meat showed the characteristics of good water retention,dark meat color,large shear force and high cooked meat rate.2.Study on Morphological Characters and Fatty Acid Composition of Adipose Tissues in Different Fat-tailed SheepIn order to study the differences of fat deposition in different fat-tailed sheep,abdominal subcutaneous fat,tail fat,perirenal fat,omentum fat and longissimus dorsi muscle were collected from different fat-tailed sheep(Every 6 8-month-old LFTS,STHS and TS sheep).The histological characteristics of each tissue were studied by the histological method.The fatty acid composition and content in samples were analyzed by cold extraction and gas chromatography.Results showed that the differences of adipocytes in adipose tissues of sheep with different fat-tail types were observed,including the sizes and densities of adipocytes in the adipose tissues of the tails,and there was no significant difference between TS?s and LFTS?s(P>0.05),but there was a significant difference with STHS?s(P<0.05).Perirenal,omentum and subcutaneous adipose tissue: There was no significant difference between STHS?s and LFTS?s(P>0.05),but there was a significant difference with TS?s.There was no significant difference in perirenal fat,omental fat and subcutaneous fat between TS and STHS in different parts of the same sheep(P>0.05),and LFTS?s subcutaneous fat and perinephric fat(P>0.05)were significantly different from its omental fat and caudal fat(P<0.05).In terms of fatty acid composition,there was no significant difference in the contents of main unsaturated fatty acids c14:0,c16:0 and c18:0 in muscle tissues of sheep with different fat-tail types(P>0.05),and no significant difference in the contents of main unsaturated fatty acids c18:1n9c(P>0.05),and C16:1 content in STHS was significantly higher than that of LFTS(P<0.05),C18:2n6c content in LFTS was significantly higher than that of TS(P<0.05),and there was no significant difference in SFA,PUFA,MUFA,P:S in muscle(P<0.05).There was no significant difference in the content of SFA among the three fat-tailed sheep in the same parts of different breeds(P>0.05).The content of PUFA in the greater omentum adipose tissue of LFTS was significantly higher than that of TS and STHS(P<0.05),and the content of PUFA in intramuscular fat was significantly higher than that in adipose tissue(P<0.05).The MUFA content of tail fat was the highest among different parts of the same breed.The MUFA content of LFTS showed a significant difference between visceral fat and subcutaneous fat(P<0.05).The MUFA content of TS showed that of subcutaneous fat was significantly greater than that of peritoneal fat(P<0.05).P:S in the greater omentum fat and caudal fat of LFTS was significantly higher than those in the other two types of sheep(P<0.05).There was no significant difference in the P:S value between the perirenal fat and subcutaneous fat(P>0.05),but the value of LFTS was the highest.From the histological and morphological comparison results,various histological analyses should be carried out between the adipose tissue in the tail and the perirenal adipose tissue of LFTS,LFTS and STHS adipose tissues in the follow-up studies,and to select the differentially expressed genes,proteins,ncRNA and other regulatory factors is helpful to further study the regulatory mechanism of body fat distribution in sheep with different tails.3.Screening and Functional Study of Differential MicroRNAs in Adipose Tissues of Different Fat-tailed SheepIn order to screen the key miRNAs,affecting adipocyte differentiation and lipid metabolism in sheep,the adipose tissues of adult LFTS and STHS were sequenced with high throughput miRNA,and the results were analyzed by high throughput sequencing and bioinformatics.11 kinds of differentially expressed miRNAs,were screened out to regulate adipose tissues,of which 6 kinds of miRNAs were significantly different in different adipose tissues(P<0.05).There were 6 kinds of differentially expressed miRNAs,in the fat of STHS and TS,of which miR-133,miR-218 a and miR-381-3p,were up-regulated,and miR-21,miR-194 and miR-200 c were down-regulated.Among them,four kinds of miRNAs(miR-133,miR-194,miR-200 c and miR-381-3p)are widely conservative among species.Six miRNA target genes differentially expressed in adipose tissue of LFTS and STHS were predicted,and a total of 35 target genes were obtained,and the functional annotation showed that these target genes were involved in a variety of physiological and pathological regulatory processes related to fat metabolism.In order to explore the effects of miR-133,miR-194,miR-200 c and miR-381-3p on fat proliferation,3T3-L1 cells were transfected with miR-133,miR-194,miR-200 c,miR-381-3p NC and mimics,and cyclinD1,PCNA and CDK2 mRNA were evaluated during the proliferation of 3T3-L1 cells.The results showed that miR-133,miR-194 and miR-381-3p significantly increased the mRNA expression level of cyclinD1 gene,and miR-133,miR-194,miR-200 c and miR-381-3p significantly decreased the mRNA expression level of PCNA and CDK2 genes.At 0h,24 h and 48 h,the expressions of cyclinD1,PCNA and CDK2 in 3T3-L1 cells overexpressing miR-194 were significantly down-regulated.The results showed that miR-194 could inhibit the proliferation of adipocytes.4.Study on Genetic Variation of SIRT7 Gene Related to Body Fat Distribution in Sheep and Its Genetic EffectSatur sheep and Mongolian sheep,two representative wool and meat purposed breeds,and LFTS,STHS,Tong sheep,Tan sheep and Hu sheep,five representative local sheep breeds were selected,totaling 709 sheep.The potential Indel loci of sheep SIRT7 gene in different sheep breeds were detected,and the relationship between sheep SIRT7 gene and sheep growth traits was discussed.the results showed that there were two new indels loci in sheep indels gene,namely 5?UTR-insertion-7 bp and 3?UTR-insertion-17 bp.It was detected in sheep for the first time.In all sheep breeds,the mutation frequency of 5? promoter region-7bp was very low,but in Tong sheep and LFTS,the mutation frequency of 3? UTR-17 bp was very high.Moreover,the results of association analysis showed that these new indels polymorphisms were significantly correlated with sheep growth traits(P<0.05).For example,3?UTR-17 bp polymorphism was highly correlated with rump width of STHS(P <0.01).Individuals with the ID genotype had better chest depth than those with the II genotype,suggesting that these new indels loci could serve as potential DNA markers for screening high-quality individuals in sheep breeding. |
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