| Forage is the main feed source for livestock.The cost of forage accounts for the highest proportion of total cost of production of of sheep under stall-feeding condition,accounting for 65%~70%.Moreover,the cost of forage is also increased correspondly with the rising price of feed raw materials.Therefore,improving the feed efficiency of sheep can make full use of the forage resources,reduce the feed cost of sheep in house and improve the economic benefits of sheep under stall-feeding condition.Furthermore,the improvement of feed efficiency is also of immense strategic importance for protecting the ecological environment and achieving sustainable development.Residual feed intake(RFI)is an ideal breeding index to measure feed utilization efficiency of sheep.On the basis of systematic performance measurement,the characteristics of feed efficiency-related traits and estimation of genetic parameters were studied.Using 16 S rDNA sequencing and transcriptome sequencing,this study investigated the relationship between RFI and rumen microflora and gene expression in liver tissue of sheep.1.Characteristic analysis and heritability estimation of traits related to feed efficiency in experimental populationIn this study,59 traits(199 indicators)including RFI,growth traits,carcass traits,body composition and muscle quality of 207 Hu lambs from 41 paternal half-sib families were systematically measured.The results showed that the feed conversion ratio(FCR)of Hu lambs increased with age during 80-180 days.The average value of FCR was 5.77 and the coefficient of variation was 10.02%,indicating its high selection potential.The estimated heritability of FCR,RFI,average daily feed intake(ADFI)and average daily gain(ADG)were 0.65,0.40,0.62 and 0.37,respectively,which belonged to middle and high heritability traits.2.Study on growth traits,carcass traits,body composition and muscle quality of lambs with different RFIThe experimental population was divided into three groups according to the individual RFI value: high-RFI(RFI > mean + 0.5SD),medium-RFI(mean-0.5SD < RFI < mean + 0.5SD)and low-RFI(RFI < mean-0.5SD).The variance analysis of the performance of growth traits,carcass traits,body composition and muscle quality of sheep among different RFI groups,it was found that the tail fat weight and its relative weight,perirenal fat and its relative weight and GR value of low-RFI sheep were significantly or very significantly lower than those of high-RFI sheep(P < 0.05 or P < 0.01).The results of correlation analysis showed that RFI was positively correlated with FCR and ADFI(P < 0.01),but not with growth traits such as body weight,metabolic weight and daily gain(P > 0.05),indicating the selection of RFI could improve feed efficiency,reduce feed intake and reduce body fat deposition of sheep.3.Study on rumen microbial diversity of lambs with different RFIThe 16 S rDNA of rumen microorganisms was sequenced by IonS5 TMXL sequencing platform,and 6.2 Gb clean data was obtained,with an average of 320 Mb clean data per sample.The effective data was 93.96%.Alpha diversity and Beta diversity indices were significantly different among different RFI groups.The number of species,Chao1 and ACE observed in low-RFI group were significantly higher than those in high-RFI group,while goods_coverage was significantly lower than that in high-RFI group.Beta diversity index in low-RFI group was significantly lower than that in high-RFI group.The species and abundance of dominant microflora were basically the same in the rumen microflora of lambs of different RFI groups,and the difference was mainly in the relatively low abundance of microflora.On the phylum level,the abundance of Tenericutes in the rumen of low-RFI lambs was significantly lower than that in high-RFI lambs(P < 0.05),while Kiritimatiellaeota was significantly higher than that of high-RFI lambs(P<0.05).On the generic level,the abundance of unidentified_Prevotellaceae,Succiniclasticum,Oribacterium,unidentified_Veillonellaceae,Desulfovibrio in the rumen of lambs in the low-RFI group was significantly lower than those in the high-RFI group(P < 0.05),while the abundance of Saccharofermentans,Papillibacter,Anaeroax in the low-RFI group was significantly higher than those in the high-RFI group(P < 0.05).4.Analysis of transcriptome in liver tissue with extremely high and low RFI lambsThree sheep with the highest and lowest RFI values were selected from the above experimental groups,and their liver tissues were sequenced using Illumina HiSeqTM2500 sequencing platform.Totally102.15 Gb clean data were obtained,with an average of 17.025 Gb per sample and Q30 was above 91%.101 differentially expressed genes(DEGs)were screened according to the standard P < 0.05 and log2FoldChange(> 2),of which 61 were up-regulated and 40 were down-regulated.All DEGs were mainly concentrated in metabolic and immune-related processes.The DEGs involved in metabolic processes were up-regulated in liver tissues of lambs in low-RFI group,while those involved in immune-related processes were up-regulated in liver tissues of lambs in high-RFI group.5.SNPs scanning of differentially expressed genes and their association with FCRThe ADRA2 A and RYR2 genes,two differentially expressed genes related to metabolism which were identified from liver tissues of High-and Low-RFI sheep,are taken as target genes.SNPs scanning of these two genes and their association with feed conversion rate were performed in expanded population.The results showed synonymous mutations,ADRA2 A g.1429 C>A and RYR g.1117 A>C,were identified in ADRA2 A and RYR2 genes.ADRA2 A g.1429 C>A polymorphism was significantly associated with FCR.The FCR value of lambs with CC genotype(4.67±0.69)are lower than those with CA(5.18±0.92)and AA(5.14±0.93)genotypes(P < 0.01),and it means that the lambs with CC genotype consume 0.51 and 0.47 kg less feed per kg gain than those with CA and AA individuals.RYR g.1117 A>C polymorphism was significantly associated with FCR.The FCR value of lambs with AA genotype(5.57±0.67)are higher than those with CA(5.19±0.66)and CC(5.24±0.58)genotypes(P < 0.05),and it means that the lambs with AA genotype consume 0.38 and 0.33 kg more feed per kg gain than those with CA and CC individuals. |
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