Polymorphisms of ACACB Gene and Their Association with Milk Quality Traits in Yak

Abstract

Acetyl-CoA carboxylase beta (ACACB) is a rate-limiting enzyme involved in lipid syn-thesis and fatty acid oxidation. The results of our previous study showed that a total of seven SNPs were detected in the exon 37-intron 37, exon 46-intron 46, and intron 47 regions of the yak ACACB, and mutations in the ACACB were found to affect yak meat quality traits. However, the genetic effects of ACACB on yak milk quality traits have not been reported. Therefore, the aim of this study was to investigate the effects of ACACB polymorphisms on yak milk quality traits in Gannan yaks. In this study, A total of 202 Gannan yaks were included in the study. Analyze the different geno-types, diplotypes, and the presence or absence of haplotypes on milk quality. The seven SNPs were named as exon 37-intron 37 (exon 37: SNP1, intron 37: SNP2 and SNP3), exon 46-intron 46 (exon 46: SNP4, intron 46: SNP5), and intron 47 (SNP6 and SNP7). Apart from the SNP1, SNP2, SNP5, and SNP6 loci where the polymorphic information content (PIC) was low (PIC ≤ 0.25), the SNP3, SNP4, and SNP7 loci were all of intermediate polymorphic information status (0.25 < PIC < 0.5). The highest frequency of heterozygosity occurred at the SNP7 locus, and the two alleles were evenly distributed in the population compared to alleles at the other loci. There were no strong linkages between the SNPs (r2<0.33) except for a strong linkage disequilibrium observed between SNP1 and SNP2 (r2=0.89). Seven effective haplotypes and seven diplotypes were constructed for the Gannan yak ACACB gene. Correlation analysis showed that SNP1 and SNP7 were associated with lactose content (P<0.05), while SNP3 was significantly associated with the protein and monounsaturated fatty acid contents in the milk (P<0.05). SNP4 was significantly associated with both saturated and monounsaturated fatty acid contents (P<0.05 and P<0.01, respectively), while SNPs 5 and 7 were significantly correlated with the fat percentage (P<0.05) and SNP6 was significantly correlated with total solid content of the milk (P<0.05). Yaks with the H2H2 diplotype had significantly higher levels of milk fat than other diplotypes (P<0.05) while milk fat contents in animals carrying hap-lotype H2 were significantly higher than that in yaks carrying the deletion type (P<0.05). The findings of the present study suggest that polymorphisms in the yak ACACB affect milk quality and can be used as genetic markers for enhancing milk quality in yak populations. The findings provide a theoretical basis for the genetic characterization of milk quality traits in the Gannan yak.