Background: Fatty acid composition has become an important trait in the beef industry in terms of beef flavor and decreasing the circulating concentration of LDL cholesterol. In this study, we examined the association between polymorphisms of six genes, adipocytes-type fatty acid binding protein (FABP4), liver X receptor α (LXRα), cytochrome b ₅ (Cyt b ₅), long-chain acyl-CoA synthetase (ACSL) 1, ACSL4 and diacylglycerol acyltransferase 2 (DGAT2) and fatty acid composition. Results: Sequence comparisons revealed 14 single nucleotide polymorphisms in six genes. Four of them, I74V and V110M in FABP4 and G51E and V133I in LXRα, were nonsynonymous substitutions. The associations between the genotypes and fatty acid compositions were analyzed by using 234 Japanese Black cattle. The genotypes of FABP4 I74V and LXRα V133I were significantly associated with palmitoleic acids (C16:1, P = 0.0086) and linoleic acid (C18:2, P = 0.0121) content in intramuscular fat, respectively. Conclusion: Our findings suggest that the two polymorphisms of FABP4 I74V and LXRα V133I might be genetic factors in part associated with palmitoleic acid (FABP4 I74V) and linoleic acid (LXRα V133I) composition in intramuscular fat of Japanese Black cattle, respectively. Especially, FABP4 I74V had highly significant effect (P < 0.01) on C16:1 proportion, indicating that the I/I homozygote exhibited 0.5% higher percentage than V/V homozygote.

The complete mtDNA D-loop regions of Japanese and Korean cattle were analyzed for their mtDNA variations and genetic relationships. Sequencing the 30 Higo substrain and 30 Tosa substrain of Japanese Brown, respectively 12 and 17 distinct Bos haplotypes were identified from 77 polymorphic nucleotide sites. In order to focus on the relationships among Japanese and Korean cattle, two types of phylogenetic tree were constructed using individual sequences; first, a neighbor-joining tree with all sequences and second, reduced median networks within each Japanese and Korean cattle group. The trees revealed that two major mtDNA haplotype groups, T3 and T4, were represented in Japanese and Korean cattle. The T4 haplogroup predominated in Japanese Black and Japanese Brown cattle (frequency of 43.3-66.7%), while the T3 haplogroup was predominant (83.3%) and T4 was represented only twice in the Korean cattle. The results suggested that the mitochondrial origins of Japanese Brown were Japanese ancient cattle as well as Japanese Black in despite of the considerable introgression of Korean and European cattle into Japanese Brown.