Body Mass Index And Its Relationship With MC4R Gene And Litter Size In Sheep

Body mass index(BMI)is an important index to measure the body energy reserve.In human,BMI has been proved to have latitude effect.MC4R and FTO genes have been proved to be most closely related to BMI.However,few studies focus on whether there is latitudinal effect on sheep BMI,whether the BMI of sheep is related to these two genes and whether the change of BMI will affect the reproductive performance of sheep.So,our study on genetic variation related to sheep BMI and the relationship between BMI geographical location and environmental factors,sheep reproduction can provide theoretical basis and new direction for improving sheep growth and reproductive performance.We defined the formula to calculated sheep BMI as BMI=BW/BL~2,in which BW is body weight(kg),and BL is body length(m),referring to the formula of human body mass index.(1)In this study,the data of adult body weight,body length,geographical location and environmental factors of 42 Chinese sheep breeds were collected to analyze the relationship between BMI and breed,gender,geographical and environmental factors.(2)we also collected the whole genome sequencing data of Bayinbuluke sheep,Cele black sheep,Hu sheep,small tail Han sheep,Tan sheep and Ujimqin sheep,and detected the single nucleotide polymorphism(SNP)of MC4R and FTO gene.(3)In addition,the body weight,body length and litter size of 327 Hu sheep were measured.We sequenced the exons of MC4R and FTO genes in these Hu sheep,and analyzed the relationship between BMI and SNP,BMI and litter size.The results are as follows:(1)The average BMI of Chinese sheep was 100.871±20.488(male vs female are107.249 VS 94.494,respectively).The Mongolian sheep BMI was 101.450±21.315(male vs female was 107.847 VS 95.052,respectively).The Tibetan sheep BMI was93.330±7.383(male vs female was 95.156 VS 91.503 respectively).The BMI of Kazakh sheep was 107.361±25.621(male vs female was 118.254 VS 96.468 respectively).Ram BMI was significantly greater than that of ewe(p<0.05).The higher the latitude,the larger the BMI(p<0.05).Altitude had no significant effect on BMI(p>0.05).The regression equation of BMI and environmental factors is BMI=2.151E-15-0.347AAP+0.585RH+0.302AASD(R~2=0.194).(2)The polymorphism of exon of two genes in 70 sheep of 6 breeds was detected,10 SNPs were found in MC4R and 9 SNPs in FTO.Among the six sheep breeds,the shannon’s information index and observational heterozygosity of Hu sheep were higher than that of other sheep breeds.The frequencies of g.519G>C and g.93C>T of MC4R were significantly correlated with BMI(p<0.05).(3)The regression between BMI and reproductive traits showed that BMI significantly affected litter size(p<0.05).The polymorphism of exon of two genes in327 Hu sheep was detected,9 SNPs were found in MC4R.Sheep with genotype CG had higher BMI than those with CC genotype(p<0.05).There were no significant differences in BMI between diplotypes of MC4R(p>0.05).12 SNPs in FTO.There was no significant difference in BMI among different genotypes of each loci of FTO(p>0.05).There were also no significant differences in BMI between diplotypes of FTO(p>0.05).