Genetic regulation of the healthfulness of beef fatty acid composition

The effects of genetic factors, such as breed and single nucleotide polymorphisms (SNPs), on beef fatty acid composition were investigated in the current study. The first objective was to identify single nucleotide polymorphisms (SNPs) in the thioesterase (TE) domain of bovine fatty acid synthase (FASN) gene and evaluate the extent to which they were associated with beef fatty acid composition. The four exons in FASN that encode for TE were sequenced, and three SNPs, AF285607:g.17924A>G, g.18663T>C, and g.18727C>T, were identified. Purebred Angus bulls (n = 331) were classified into three genotype groups, AA (n = 121), AG (n = 168), and GG (n = 42), based on SNP g.17924A>G. The g.17924A>G genotype was significantly associated with fatty acid composition of longissimus dorsi (LD) muscle of purebred Angus bulls. Cattle with the GG genotype had lower myristic acid (C14:0; P < 0.0001) and total saturated fatty acids contents (SFA; P < 0.01), greater health index (HI; P < 0.001), oleic acid content (C18:1; P < 0.001), and total monounsaturated fatty acids concentrations (MUFA; P < 0.01) in the total lipids and triacylglycerols (TAG) fraction than did those with the AA genotype. Because of the linkage disequilibrium between SNPs g.17924A>G and g.18663T>C, similar significant associations of fatty acid contents with the g.18663T>C genotypes were observed. In conclusion, the SNPs g.17924A>G and g.18663T>C may be used as DNA markers to select breeding Angus cattle that have a healthier fatty acid composition.;The second objective of this study was to identify single nucleotide polymorphisms (SNPs) in the promoter I (PI) region of bovine acetyl-CoA carboxylase-alpha (ACC-alpha) gene and evaluate the extent to which they were associated with lipid content and fatty acid composition of beef. Eight novel single nucleotide polymorphisms (SNPs) were identified. Complete linkage disequilibrium was observed among 6 of the 8 SNPs. Phenotypic data were collected from 573 cross-bred steers. The association of genotypes determined by each SNP with lipid content and fatty acid composition was investigated. A mixed model was used for the statistical analysis that included genotype, sire line, and dam line as fixed effects and contemporary groups as random effect. The genotype of SNP g.2350T>C was significantly associated with the lipid content of beef (P < 0.05). No significant association, however, was detected between the genotype of any SNPs with fatty acid composition.;The last objective of this study was to estimate the effects of sire breed on fatty acid composition of triacylglycerols (TAG), phospholipids (PL), and total lipids extracted from bovine Longissimus muscle (LM). Steer progeny resulting from artificial insemination mating of Angus and MARC III females with Hereford, Angus, Brangus, Beefmaster, Bonsmara, and Romosinuano males were used in the current study. Angus-sired steers had the greatest content of total lipids in LM, which could be attributed to its greatest content of TAG in LM. The concentration of each individual fatty acid in TAG was significantly affected by the sire breed. Bonsmara-sired steers had the greatest content of myristic acid (C14:0) and the lowest concentration of total MUFA compared with steers from other sire breeds. The index of atherogenicity (IA) was therefore greater in Bonsmara-sired steers than in progeny of other sire breeds. High negative correlation (r = -0.98) was observed between the content of total SFA and MUFA in TAG after accounting for the known sources of variation from the analysis model. The concentrations of fatty acids were less influenced by sire breed in PL than those in TAG. The content of total SFA and the value of IA did not differ significantly among the steers with different sire breeds. Great negative correlation was observed between the content of total MUFA and PUFA in PL (r = -0.91). Because more than 90% of the lipids in LM were TAG, the fatty acid composition in total lipids was similar as that in TAG. Bonsmara-sired steers had the greatest IA, whereas Romosinuano-sired steers had the lowest IA in total lipids. In conclusion, these results suggest that sire breed is an important source of the variation for fatty acid composition of TAG, PL, and total lipids in LM.