| East Friesian sheep is the sheep breed with the best lactation performance in the world at present,and Hu sheep is an excellent local multi-litter sheep breed in China.The dairy group formed by crossing East Friesian sheep and local breed Hu sheep(East Friesian and Hu crossbred sheep),which has broadened our country’s sheep industry to use both milk and meat and adapted to the local ecological environment.Based on the group litter size data of East Friesian and Hu crossbred sheep,this study combined with the data of breeding mode and lambing season to reveal the important external factors affecting the litter size..Through the data of Genome-wide association studies(GWAS)and the litter size of168 East Friesian and Hu crossbred sheep,GWAS was conducted to analyze the important candidate genes or variation loci affecting lambing,and then the genotyping of the candidate loci was conducted to reveal their distribution in large populations and verify the results of GWAS.In order to provide molecular markers for the breeding of multiple lambs in East Friesian and Hu crossbred sheep,and promote the healthy and efficient development of dairy sheep industry.The results obtained in this study are as follows:1.In this study,SPSS software was used to conduct correlation analysis between year,season,breeding method and the lamb number of 1907 East Friesian and Hu crossbred sheep,and it was found that the three factors can significantly affect the sheep litter sizer.Based on the data of the three parities,the average litter size in spring was significantly increased compared with other seasons(p < 0.01),and the average litter size in the first litter was significantly increased by 0.16 in natural breeding compared with artificial breeding(p <0.01).These results will be helpful for the selection of mating methods and mating time in actual production.2.Through the GWAS of the whole genome data of 168 East Friesian and Hu crossbred sheep and the litter size,1163 SNP loci reaching the significance level on chromosome 6were identified.Through the annotation of candidate loci,The candidate genes BMPR1 B,PDLIM5,PDHA2,UNC5 C,GRID2,NFKB1,TSPAN5,STPG2 and PPP3 CA related to litter size were determined.Combined with previous reports and the annotations of the strongest associated regions,BMPR1 B may be a candidate gene affecting the multiple litter traits of East Friesian and Hu crossbred sheep.3.Two SNPS(g.35685218A>G and g.35685499C>T)on GRID2 in genome-wide association analysis were selected as candidate loci,and competitive Allele-Specific PCR(Kompetitive Allele-specific PCR,The genotypic distribution of 560 Donghu hybrid dairy sheep was detected by KASP.The average number of lambs of wild type at locus35685218A>G was increased by 0.36 compared with heterozygous type,and that of mutant type was increased by 0.93.g.35685499C>T site wild-type increased the average number of lambs by 0.23 compared with heterozygous type,and 0.88 compared with mutant type.Wild-type at both sites was in a dominant state.In summary,this study focused on the litter size of East Friesian and Hu crossbred sheep and revealed the external influencing factors and important candidate genes affecting the litter size through significant association analysis,genome-wide association analysis and other means.Based on the results of GWAS,the distribution of g.35685218A>G and g.35685499C>T in GRID2 gene in East Friesian and Hu crossbred sheep population and their correlation with litter size were further explored.This study provides a solid theoretical basis for improving the litter size of dairy sheep and promoting the genetic breeding progress of dairy sheep. |
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