A comparison of fat composition of Japanese and long-term grain-fed Australian steers

Muscle biopsy long-chain omega-3 polyunsaturated fatty acid compositions, IMF and FMP in Australian pasture-based Bowen Genetics Forest Pastoral Angus, Hereford, and Wagyu Beef Cattle

BACKGROUND

We investigated breed and gender variations in the compositions of long-chain (≥ C20) omega-3 polyunsaturated fatty acids (LC omega-3 PUFA), fat melting point (FMP) and intramuscular fat (IMF) contents in biopsy samples of the M. longissimus dorsi muscle of grazing beef cattle. The hypothesis that biopsy compositions of health-beneficial LC omega-3 PUFA, FMP and IMF in a pasture-based production system will vary with breed, was tested. Muscle biopsies were taken from 127 yearling pasture-based Angus, Hereford, and Wagyu heifers and young bulls exclusive to the Australian Bowen Genetics Forest Pastoral breeding stud averaging 12 ± 2.43 months of age and under the same management routine.

RESULTS

Breed had a significant influence on IMF, FMP, and the compositions of oleic acid, α-linolenic acid (ALA), eicosapentaenoic (EPA), docosahexaenoic (DHA), docosapentaenoic (DPA), and total EPA + DHA + DPA in the M. longissimus dorsi muscle biopsies (P ≤ 0.03). The Wagyu breed had the highest (11.1%) and Hereford the lowest (5.9%) IMF (P = 0.03). The reverse trend was observed in FMP values where the Hereford breed had the highest (55 °C), Angus intermediate (46.5 °C), and Wagyu the lowest (33 °C) FMP. The Wagyu and Angus breeds had similar oleic fatty acid (18:1n-9) content, while the Hereford breed had the lowest (P < 0.01). The highest ALA, DPA, total EPA + DHA, total EPA + DHA + DPA and total ALA + EPA + DHA + DPA contents were detected in the Wagyu breed (P ≤ 0.03). The Hereford had similar EPA and DPA contents to the Angus (P ≥ 0.46). Total EPA + DHA + DPA contents in Wagyu, Angus, and Hereford were 28.8, 21.5, and 22.1 mg/100g tissue (P = 0.01), respectively. Sex was an important source of variation that influenced LC omega-3 PUFA composition, FMP and IMF, where yearling heifers had higher IMF (11.9% vs 5.3%), lower FMP (33°C vs 37°C), and higher LC omega-3 PUFA than bulls.

CONCLUSION

All the results taken together indicate that the Wagyu breed at 28.8 mg/100g tissue, was the closest to meeting the Australia and New Zealand recommended source level threshold of 30 mg/100g tissue of health-beneficial ≥ C20 omega-3 FA content. Since gender was a significant determinant of LC omega-3 PUFA composition, IMF content and FMP, it should be factored into enhancement strategies of healthy meat eating quality traits in grazing cattle. These findings also suggest that the Bowen Genetics Forest Pastoral beef cattle studs are important sources of LC omega-3 PUFA that can be used to cover the deficit in these health claimable fatty acids in Western diets.

Application of linear and machine learning models to genomic prediction of fatty acid composition in Japanese Black cattle

We collected 3180 records of oleic acid (C18:1) and monounsaturated fatty acid (MUFA) measured using gas chromatography (GC) and 6960 records of C18:1 and MUFA measured using near-infrared spectroscopy (NIRS) in intermuscular fat samples of Japanese Black cattle. We compared genomic prediction performance for four linear models (genomic best linear unbiased prediction [GBLUP], kinship-adjusted multiple loci [KAML], BayesC, and BayesLASSO) and five machine learning models (Gaussian kernel [GK], deep kernel [DK], random forest [RF], extreme gradient boost [XGB], and convolutional neural network [CNN]). For GC-based C18:1 and MUFA, KAML showed the highest accuracies, followed by BayesC, XGB, DK, GK, and BayesLASSO, with more than 6% gain of accuracy by KAML over GBLUP. Meanwhile, DK had the highest prediction accuracy for NIRS-based C18:1 and MUFA, but the difference in accuracies between DK and KAML was slight. For all traits, accuracies of RF and CNN were lower than those of GBLUP. The KAML extends GBLUP methods, of which marker effects are weighted, and involves only additive genetic effects; whereas machine learning methods capture non-additive genetic effects. Thus, KAML is the most suitable method for breeding of fatty acid composition in Japanese Black cattle.

Effects of chilling duration on USDA Quality Grade of beef carcasses

Two hundred and nine beef carcasses (BW of 361 ± 53 kg) from crossbred, grain-finished cattle were harvested in a commercial abattoir and subjected to a 96-h spray chilling treatment, conducted at 0 to 3°C in a commercial hot box with a wind speed of 3.1 m/s and 153-lux of fluorescent light. At the 24, 48, 72, and 96 h points of the treatment, the carcasses were analyzed for fatty acid composition, marbling score, core temperature (n = 1), pH, shrinkage, color, and aerobic plate count (n = 50). Carcasses reached 3ºC after 12 to 16 h of chilling. There were minimal changes in shrinkage among time point (-0.4 to 1.2%; P ≤ 0.002), pH (5.56 to 5.69; P ≤ 0.001), and aerobic plate count (APC) (0.1 to 0.7 log; P ˂ 0.001). Initial 24-h grading revealed a grade composition of 21.1% Slight (SL, n = 44), 34.0% Small (SM, n = 71), 17.2% Modest (MT, n = 37), 17.7% Moderate (MD, n = 36), and 10.1% Slightly Abundant (SA, n = 21). With marbling score in numeric values between 200 (Practically Devoid00) and 1100 (Abundant00), carcasses that had SM or greater marbling score at 24 h experienced a deduction of 34 to 60 points by the 96th hour of spray chilling (P ≤ 0.042). Comparatively, the marbling scores of the SL carcasses increased from 442 points at 24 h to 469 points at 96 h. Moreover, SL carcasses had a greater percentage of polyunsaturated fats (PUFA) (P &lt; 0.001). Results indicate that spray chilling for 96 h may slightly increase the marbling score of USDA Select, but has minimal impacts on marbling score of greater USDA quality grades.

Effect of Five Polymorphisms on Percentage of Oleic Acid in Beef and Investigation of Linkage Disequilibrium to Confirm the Locations of Quantitative Trait Loci on BTA19 in Japanese Black Cattle

Five polymorphisms associated with the percentage of oleic acid (C18:1) in beef fat were previously reported on bovine chromosome 19 in different Japanese Black cattle populations. This study aimed to verify the effects of these five polymorphisms on C18:1 using the same Japanese Black cattle population and conduct linkage disequilibrium (LD) analysis in order to determine the locations of the quantitative trait loci (QTLs). We genotyped the five polymorphisms (SREBP1 c.1065 + 83 (84bp indel), STARD3 c.1187 C > T, GH c.379 C > G, FASN g.841 G > C, and FASN g.16024 A > G) in two populations, which were bred in Hyogo and Gifu Prefectures, Japan (n = 441 and 443, respectively) in order to analyze their effects on C18:1 using analysis of variance (ANOVA). In the Hyogo population, SREBP1 c.1065 + 83 and STARD3 c.1187 C > T were significantly associated with C18:1 (p < 0.001). Meanwhile, FASN g.841 G > C, FASN g.16024 A > G, and GH c.379 C > G were significantly associated with C18:1 (p < 0.01) in the Gifu population. LD analysis was subsequently conducted to detect the range of the QTLs, which ranged from 32.2 to 46.4 Mbp and from 47.8 to 52.1 Mbp in the Hyogo and Gifu populations, respectively. In conclusion, this study confirmed the existence of QTLs on BTA19 and divided the candidate region for each QTL based on LD coefficients. These results could contribute to efficient searches for responsible genes and polymorphisms for fatty acid composition.

Comparisons of adipogenesis- and lipid metabolism-related gene expression levels in muscle, adipose tissue and liver from Wagyu-cross and Holstein steers

The intramuscular fat (IMF) content and fatty acid composition are important meat quality traits that are mostly affected by the cattle breed. Muscle, adipose tissue and liver are important organs involved in the development of intramuscular adipose tissue. Thus, we hypothesized that there were marked differences in the adipogenesis and lipid metabolism of these tissues between Wagyu-cross and Holstein steers during the finishing phases. To test this hypothesis, we analyzed the expression levels of adipogenesis- and lipid metabolism-related genes in longissimus muscle (LM), subcutaneous fat (SCF) and liver from Wagyu-cross and Holstein steers at 26 months of age. The IMF content and fatty acid profile of LM were determined. Wagyu-cross steers had a higher IMF content and MUFA percentages in the LM than Holstein steers (P<0.05). The relative expression of FGF2, COL1A1, SREBP1c, SCD1, GRP78 and LEP was greater in the LM of Wagyu-cross steers than in Holstein steers (P<0.05). In contrast, Holstein steer SCF had higher (P<0.05) mRNA expression levels of FABP4 and ADIPOQ than Wagyu-cross steers. In the liver, the expression of SREBP1c and GRP78 in Wagyu-cross steers was significantly higher than that in Holstein steers (P<0.05). The results demonstrate that both intramuscular adipogenesis and fibrogenesis are enhanced in Wagyu-cross steers compared with Holstein steers during the finishing phase and that IMF deposition is positively correlated with the maturity of SCF and hepatic lipid accumulation in Wagyu-cross steers.

Genome wide association study identifies SNPs associated with fatty acid composition in Chinese Wagyu cattle

Background

Fatty acids are important traits that affect meat quality and nutritive values in beef cattle. Detection of genetic variants for fatty acid composition can help to elucidate the genetic mechanism underpinning these traits and promote the improvement of fatty acid profiles. In this study, we performed a genome-wide association study (GWAS) on fatty acid composition using high-density single nucleotide polymorphism (SNP) arrays in Chinese Wagyu cattle.

Results

In total, we detected 15 and 8 significant genome-wide SNPs for individual fatty acids and fatty acid groups in Chinese Wagyu cattle, respectively. Also, we identified nine candidate genes based on 100 kb regions around associated SNPs. Four SNPs significantly associated with C14:1 cis-9 were embedded with stearoyl-CoA desaturase (SCD), while three SNPs in total were identified for C22:6 n-3 within Phospholipid scramblase family member 5 (PLSCR5), Cytoplasmic linker associated protein 1 (CLASP1), and Chymosin (CYM). Notably, we found the top candidate SNP within SCD can explain ~ 7.37% of phenotypic variance for C14:1 cis-9. Moreover, we detected several blocks with high LD in the 100 kb region around SCD. In addition, we found three significant SNPs within a 100 kb region showing pleiotropic effects related to multiple FA groups (PUFA, n-6, and PUFA/SFA), which contains BAI1 associated protein 2 like 2 (BAIAP2L2), MAF bZIP transcription factor F (MAFF), and transmembrane protein 184B (TMEM184B).

Conclusions

Our study identified several significant SNPs and candidate genes for individual fatty acids and fatty acid groups in Chinese Wagyu cattle, and these findings will further assist the design of breeding programs for meat quality in cattle.

The Japanese Wagyu beef industry: current situation and future prospects - A review

In Japan, Wagyu cattle include four Japanese breeds; Black, Brown, Shorthorn, and Polled. Today, the renowned brand name Wagyu includes not only cattle produced in Japan, but also cattle produced in countries such as Australia and the United States. In recent years, the intramuscular fat percentage in beef (longissimus muscle) from Japanese Black cattle has increased to be greater than 30%. The Japanese Black breed is genetically predisposed to producing carcass lipids containing higher concentrations of monounsaturated fatty acids than other breeds. However, there are numerous problems with the management of this breed including high production costs, disposal of untreated excrement, the requirement for imported feed, and food security risks resulting from various viral diseases introduced by imported feed. The feeding system needs to shift to one that is more efficient, and improves management for farmers, food security for consumers, and the health environment for residents of Japan. Currently, we are developing a metabolic programming and an information and communications technology (ICT, or Interne of Things) management system for Wagyu beef production as future systems. If successful, we will produce safe, high-quality Wagyu beef using domestic pasture resources while solving the problems of how to utilize increasing areas of abandoned agricultural land and to make use of the plant-based feed resources in Japan’s mountainous areas.

Evaluation of the thermal property of bovine intramuscular adipose tissue using differential scanning calorimetry

The thermal property of bovine intramuscular adipose tissue (IAT) was evaluated using differential scanning calorimetry (DSC) and compared with the melting point temperature (MP) of the fat extract of IAT, which was measured using the slip point method. The beef samples were classified according to the beef marbling score (BMS). Beef with a high BMS contained less protein than that with middle or low BMS. Beef with a high BMS contained significantly more fat than that with a low BMS (P < 0.05). The endothermic point temperature (EP) of IAT, measured by DSC, was significantly higher than the MP of IAT fat (P < 0.05). The EP showed no significant difference among the three marbling grade groups. Although the MP was correlated with the monounsaturated fatty acids (MUFA) content of IAT (R²  = 0.505), there was no correlation between the EP and the MUFA (R²  = 0.040). However, the EP of IAT treated with collagenase was relatively highly correlated with the MP (R²  = 0.655). Thus, these results suggested that DSC analysis would give us the practical thermal information regarding the melt-in the-mouth of beef such as the gelatinization of collagen, along with the melting of fat in IAT.

Characteristics and Health Benefit of Highly Marbled Wagyu and Hanwoo Beef

This review addresses the characteristics and health benefit of highly marbled Wagyu and Hanwoo beef. Marbling of Wagyu and Hanwoo beef has been increased in Japan and Korea to meet domestic consumer preferences. Wagyu and Hanwoo cattle have high potential of accumulating intramuscular fat (IMF) and producing highly marbled beef. The IMF content varies depending on the feeding of time, finishing diet, and breed type. IMF increases when feeding time is increased. The rate of IMF increase in grain-fed cattle is faster than that in pasture-fed cattle. Fatty acid composition are also different depending on breeds. Highly marbled Wagyu and Hanwoo beef have higher proportions of monounsaturated fatty acid (MUFA) due to higher concentrations of oleic acid. MUFAs have little effect on total cholesterol. They are heart-healthy dietary fat because they can lower low-density lipoprotein (LDL)-cholesterol while increasing high-density lipoprotein (HDL)-cholesterol. Clinical trials have indicated that highly marbled beef does not increase LDL-cholesterol. This review also emphasizes that high oleic acid beef such as Wagyu and Hanwoo beef might be able to reduce risk factors for cardiovascular disease.

Change of fatty acid composition of the lumbar longissimus during the final stage of fattening in the Japanese Black cattle

Consideration of the shortened fattening period seems to be worthwhile for the realization of profitable beef production. In this study, change of fatty acid composition of the lumbar longissimus during the final stage of fattening was investigated in Japanese Black cattle. Each of 110 fattening animals was sampled three times: the initial two samples were taken by biopsy (25.7 months and 27.5 months on average) and the final one was from carcasses (29.9 months on average). Preliminary analysis indicated that removing muscle tissues from the constant body position of the living animals should be essential for sampling. Average monounsaturated fatty acids (MUFA) at three sampling points were 58.1%, 58.5% and 60.5%, and the differences of the third sampling with the first and second samplings were significant. Both in steers and heifers, MUFA also increased as the fattening stage proceeded, and MUFA of the heifers at all the sampling points were significantly higher than those of the steers. The increasing rate of MUFA rose from 0.21 percentage points (pp)/month at period 1 (from the first sampling to the second sampling) to 0.84 pp/month at period 2 (from the second sampling to the slaughter).

Single Nucleotide Polymorphism in the Coding Region of Bovine Chemerin Gene and Their Associations with Carcass Traits in Japanese Black Cattle

Chemerin, highly expressed in adipose and liver tissues, regulates glucose and lipid metabolism and immunity in these tissues in ruminants and mice. Our previous reports showed that chemerin is involved in adipogenesis and lipid metabolism in adipose tissue as an adipokine. The aim of the present study was to identify single nucleotide polymorphisms (SNPs) in the coding region of the chemerin gene and to analyze their effects on carcass traits and intramuscular fatty acid compositions in Japanese Black cattle. The SNPs in the bovine chemerin gene were detected in 232 Japanese Black steers (n = 161) and heifers (n = 71) using DNA sequencing. The results revealed five novel silent mutations: NM_001046020: c.12A>G (4aa), c.165G<A (55aa), c.276C>T (92aa), c.321 A>G (107aa), and c.396C>T (132aa). There was no association between 4 of the SNPs (c.12A>G [4aa], c.165G<A [55aa], c.321 A>G [107aa], and c.396C>T) and carcass traits or intramuscular fatty acid compositions. Regarding the remaining SNP, c.276C>T, we found that cattle with genotype CC had a higher beef marbling score than that of cattle with genotype CT, whereas cattle with genotype CT had a higher body condition score (p<0.10). Further, cattle with genotype CC had significantly higher C18:0 content in their intramuscular fat tissue than that of cattle with genotype CT (p<0.05). On the other hand, cattle with genotype CT had significantly higher C14:0 and C16:0 content in their intramuscular fat tissue (p<0.05). Moreover, the number of individuals carrying the minor allele of c.276C>T SNP is small. It is suggested that the c.276C>T SNP of the chemerin gene has potential in cattle breeding using modern methods, such as marker assisted selection. So, further functional and physiological research elucidating the impact of the chemerin gene on bovine lipid metabolism including fatty acid synthesis will help in understanding these results.

Identification of exonic nucleotide variants of the thyroid hormone responsive protein gene associated with carcass traits and Fatty Acid composition in korean cattle

The thyroid hormone responsive protein (THRSP) gene is a functional gene that can be used to indicate the fatty acid compositions. This study investigates the relationships of exonic single nucleotide polymorphisms (SNPs) in the THRSP gene and fatty acid composition of muscle fat and marbling score in the 612 Korean cattle. The relationships between fatty acid composition and eight SNPs in the THRSP gene (g.78 G>A, g.173 C>T, g.184 C>T, g.190 C>A, g.194 C>T, g.277 C>G, g.283 T>G and g.290 T>G) were investigated, and according to the results, two SNPs (g.78 G>A and g.184 C>T) in exon 1 were associated with fatty acid composition. The GG and CC genotypes of g.78 G>A and g.184 C>T had higher unsaturated fatty acid (UFA) and monounsaturated fatty acid (MUFA) content (p<0.05). In addition, the ht1*ht1 group (Val/Ala haplotype) in a linkage disequilibrium increased MUFAs and marbling scores for carcass traits (p<0.05). As a result, g.78 G>A and g.184 C>T had significantly relationships with UFAs and MUFAs. Two SNPs in the THRSP gene affected fatty acid composition, suggesting that GG and CC genotypes and the ht1*ht1 group (Val/Ala haplotype) can be markers to genetically improve the quality and flavor of beef.

Identification of novel single nucleotide polymorphisms (SNPs) of the lipoprotein lipase (LPL) gene associated with fatty acid composition in Korean cattle

The lipoprotein lipase (LPL) gene can be considered a functional candidate gene that regulates fatty acid composition. In this study, genetic associations between fatty acid composition and exonic single nucleotide polymorphisms (SNPs) in the LPL gene were examined using 612 Korean cattle. We investigated the relationship between unsaturated fatty acids and five novel SNPs (c.322G>A, c.329A>T, c.527T>G, c.988C>T and c.1591G>A), and confirmed that three polymorphic SNPs (c.322G>A, c.329A>T and c.1591G>A) were associated with fatty acid composition. Korean cattle with an AA genotype of c.322G>A, c.329A>T, and GA genotype of c.1591G>A had higher levels of monounsaturated fatty acids and carcass traits (P < 0.05). Our findings confirmed that three novel SNPs we identified in the LPL gene can affect fatty acid composition and carcass traits. Therefore, selection for AA and GA genotypes should be recommended to genetically improve beef quality and flavor.

Identification and utilization of genes associated with beef qualities

The fatty acid composition of adipose tissue in beef has been recognized as an important trait because of its relationship with beef quality, including favorable beef flavor and tenderness. Over the last decade, we have tried to identify the genes responsible for the fatty acid composition in cattle, and have found the following. (i) Genetic polymorphism of stearoyl-CoA desaturase (SCD) is one of the responsible genes associated with fatty acid composition. The average effects of gene substitution of the SCD type A gene on the monounsaturated fatty acid (MUFA) percentage and the melting point of intramuscular fat were approximately +1.0% and -1.0°C, respectively. (ii) Intron polymorphism of sterol regulatory element binding protein-1 (SREBP-1) also affected MUFA. (iii) No effect of SCD or SREBP-1 genotypes on any representative carcass traits of Japanese Black in the field population was observed. (iv) Additional genetic markers adipocytes fatty acid binding protein 4 (FABP4) and liver X receptor α also affected the fatty acid composition. (v) SCD and FABP4 significantly affected fatty acid composition in Holstein steers. These findings will bring new insight into the fat-related carcass traits of beef cattle and will thus contribute to the beef industry.

Relationship between adipose maturity and fatty acid composition in various adipose tissues of Japanese Black, Holstein and Crossbred (F1) steers

The amount of monounsaturated fatty acid (MUFA) is intimately related to adipose softness, melting point (MP) and flavor in beef. Stearoyl-CoA desaturase (SCD) is a main gene involved in MUFA synthesis. Mature adipose tends to be highly saturated, whereas immature or maturing adipose is highly unsaturated when chronologically based, so the degree of non-saturation can be an index of adipose maturity. In this study, three different adipose tissues (coelomic (CL), perirenal (PR), and subcutaneous (SC)) from three beef breeds with differing slaughter ages (Japanese Black (29.5 months), Holstein (20.1 month), and F1 crossbreed (25.6 months)) were examined to: (i) determine adipose maturity level as indexed by MUFA %; and (ii) determine SCD and other lipogenic gene messenger RNA (mRNA) expression levels in relation to unsaturated fatty acid content. Fatty acid composition was significantly different between adipose tissues (P < 0.05). MUFA amount was high in the following order: SC > CL > PR. This pattern corresponded to SCD mRNA expression profile showing higher expression in SC than CL and PR. However, Japanese black cattle are an exception with CL adipose containing similar UFA % as SC adipose, yet having the lowest SCD mRNA expression level among all adipose tissues tested. Therefore, SCD mRNA expression and MUFA % appear to be directly related; however, differences in SCD mRNA expression among three adipose tissues may reflect differences in the fat development characteristics affected by chronological age of the cattle breeds.

Effects of GH gene polymorphism and sex on carcass traits and fatty acid compositions in Japanese Black cattle

To investigate the effects of bovine growth hormone (bGH) gene polymorphism on carcass traits and fatty acid compositions in Japanese Black cattle caused by nucleotide substitution of CTG (allele A)/GTG (allele B) at codon 127 and of ACG (allele A and B)/ATG (allele C) at codon 172 of bGH, GH genotypes of 135 cattle were determined using allele specific-multiplex polymerase chain reaction (PCR). Allele A gave greater rib thickness and lower melting point of fat (MP) while allele B gave higher C18:1% (P < 0.05). Allele C gave higher C18:1, monounsaturated fatty acid (MUFA), unsaturated fatty acid (USFA) percentages (P < 0.05). It also gave lower saturated fatty acid (SFA) percentages, higher MUFA/SFA and USFA/SFA ratios, and lower MP (P < 0.05). Interactions of sex and GH alleles were analyzed. In heifers, allele A gave higher carcass weight, daily carcass gain, rib eye area, rib thickness, subcutaneous fat thickness, and BMS while allele B gave greater rib eye area and rib thickness (P < 0.05). Allele C gave higher C18:1 (P < 0.01), MUFA (P < 0.01), USFA percentages (P < 0.05) and MUFA/SFA and USFA/SFA ratios (P < 0.01), and lower C16:0 and SFA percentages (P < 0.05) and MP (P < 0.01). GH gene polymorphism affected carcass traits and fatty acid compositions although the effects were more pronounced in heifers.

Discovery of novel genetic networks associated with 19 economically important traits in beef cattle

Quantitative or complex traits are determined by the combined effects of many loci, and are affected by genetic networks or molecular pathways. In the present study, we genotyped a total of 138 mutations, mainly single nucleotide polymorphisms derived from 71 functional genes on a Wagyu x Limousin reference population. Two hundred forty six F₂ animals were measured for 5 carcass, 6 eating quality and 8 fatty acid composition traits. A total of 2,280 single marker-trait association runs with 120 tagged mutations selected based on the HAPLOVIEW analysis revealed 144 significant associations (P < 0.05), but 50 of them were removed from the analysis due to the small number of animals (≤ 9) in one genotype group or absence of one genotype among three genotypes. The remaining 94 single-trait associations were then placed into three groups of quantitative trait modes (QTMs) with additive, dominant and overdominant effects. All significant markers and their QTMs associated with each of these 19 traits were involved in a linear regression model analysis, which confirmed single-gene associations for 4 traits, but revealed two-gene networks for 8 traits and three-gene networks for 5 traits. Such genetic networks involving both genotypes and QTMs resulted in high correlations between predicted and actual values of performance, thus providing evidence that the classical Mendelian principles of inheritance can be applied in understanding genetic complexity of complex phenotypes. Our present study also indicated that carcass, eating quality and fatty acid composition traits rarely share genetic networks. Therefore, marker-assisted selection for improvement of one category of these traits would not interfere with improvement of another.

Significant associations of stearoyl-CoA desaturase (SCD1) gene with fat deposition and composition in skeletal muscle

Gene expression studies in humans and animals have shown that elevated stearoyl-CoA desaturase (SCD1) activity is associated with increased fat accumulation and monounsaturation of saturated fatty acids in skeletal muscle. However, results of the two reported association studies in humans are inconsistent. In the present study, we annotated the bovine SCD1 gene and identified 3 single nucleotide polymorphisms (SNPs) in its 3'untranslated region (UTR). Genotyping these SNPs on a Wagyu x Limousin reference population revealed that the SCD1 gene was significantly associated with six fat deposition and fatty acid composition traits in skeletal muscle, but not with subcutaneous fat depth and percent kidney-pelvic-heart fat. In particular, we confirmed that the high stearoyl-CoA desaturase activities/alleles were positively correlated with beef marbling score, amount of monounsaturated fatty acids and conjugated linoleic acid content, but negatively with amount of saturated fatty acids. The inconsistent associations between human studies might be caused by using different sets of markers because we observed that most associated markers are located near the end of 3'UTR. We found that the proximity of the polyadenylation signal site is highly conserved among human, cattle and pig, indicating that the region might contain functional elements involved in posttranscriptional control of SCD1 activity. In conclusion, our cross species study provided solid evidence to support SCD1 gene as a critical player in skeletal muscle fat metabolism.

Genotype of bovine sterol regulatory element binding protein-1 (SREBP-1) is associated with fatty acid composition in Japanese Black cattle

To investigate genetic factors that affect fatty acid composition in beef carcass, we previously investigated genetic profiles of stearoyl-CoA desaturase (SCD) and their effect on fatty acid composition in fat tissue of cattle. It has been known that sterol regulatory element binding protein (SREBP) is a transcription factor that regulates gene expression levels of SCD and other genes relevant to lipid and fatty acid metabolism in tissue. Therefore, we determined the full-length sequence of bovine SREBP-1 cDNA and then surveyed polymorphisms in whole exons and introns in the bovine genome. Large 84-bp insertion (long type: L) and deletion (short type: S) were found in intron 5 of bovine SREBP-1 in Japanese Black cattle, although there was no notable mutation in exon regions. The associations between the SREBP-1 genotypes and fatty acid compositions/fat melting points were analyzed by using genomic DNA with carcass trait information from 606 Japanese Black cattle. The S type contributed to 1.3% higher monounsaturated fatty acid (MUFA) proportion and 1.6 degrees C lower melting point in intramuscular fat. Genotyping of bovine SREBP-1 is considered to reflect a genetic variation which is associated with physiologic characteristics of fat tissue in Japanese black cattle.

Stearoyl-CoA desaturase mRNA expression during bovine adipocyte differentiation in primary culture derived from Japanese Black and Holstein cattle

Stearoyl-CoA desaturase (SCD) catalyzes the synthesis of monounsaturated fatty acids (MUFAs). In cattle, the MUFAs are related to softness and flavor of meat. In order to investigate gene expression profile during bovine preadipocyte differentiation, we isolated stromal-vascular cells from perirenal adipose tissues of Japanese Black and Holstein steers. Gene expression level of adipocyte type fatty acid binding protein (FABP4), SCD, sterol regulatory element binding protein 1 (SREBP1) and CCAAT/enhancer binding protein alpha (C/EBP-alpha) were elucidated by real-time PCR assay. The levels of SCD mRNA expression were significantly increased to 10.8 and 6.3-fold in Japanese Black and Holstein, respectively, on day 1 of the culture. The difference in SCD expression between the two breeds may reflect differences in the fat development characteristics of the cattle breeds. Although transcription factors SREBP1 and C/EBP-alpha are supposed to regulate SCD expression, expression levels of the two factors were not completely consistent with that of SCD.

β-carotene and oxidative desaturation of fatty acids: a plausible explanation of the conflicting responses of coronary heart disease to β-carotene?

Studies of the desaturation of saturated fatty acids in animals may help explain conflicting reports of the response of coronary heart disease (CHD) to beta-carotene in humans. A negative relationship exists between desaturation and adipose beta-carotene in cattle when they consume different quantities of beta-carotene. Opposing this finding, however, is a positive relationship between desaturation and adipose beta-carotene when cattle are fed the same quantity of beta-carotene. The reason for this apparent contradiction appears to be due to differences in consumption, or variability in the metabolism of beta-carotene. Animals that efficiently metabolize beta-carotene to vitamin A have low desaturation but high antioxidant potential. These results in animals show some similarity between the consumption of the antioxidant beta-carotene and the risk of coronary heart disease where the oxidation of low-density lipoproteins (LDL) is believed to play a role in the development of atherosclerotic plaque. Genetic differences in carotenoid metabolism in humans, similar to those in animals, would assist in explaining differences in lipoprotein oxidation in humans and variation in the risk of coronary heart disease.

Genotype of stearoyl-coA desaturase is associated with fatty acid composition in Japanese Black cattle

To investigate the genetic factors that affect fatty acid composition of beef, we compared the full-length bovine stearoyl-CoA desaturase (SCD) cDNA from 20 Japanese Black steers. Two types of the SCD gene with single nucleotide polymorphisms (SNPs) were observed in the ORF of SCD cDNA, in which an amino acid replacement from valine (type V) to alanine (type A) was predicted. We developed a method for genotyping these two SCD genes based on PCR-RFLP. We have classified 1003 Japanese Black carcasses into three genotypes, VV, VA, and AA, and compared fatty acid composition among them. The SCD type A gene contributed to higher MUFA percentage and lower melting point in intramuscular fat. The SCD genotype was not the only genetic factor contributing to fatty acid composition of Japanese Black steers, but the SCD genotype was considered one of the causes of genetic variation in fatty acid composition of Japanese Black steers. Transcription factors such as sterol regulatory element binding protein-1c (SREBP-1c) may account for the remaining part of the genetic variation in fatty acid composition.

Differences in delta9 desaturase activity between Jersey- and Limousin-sired cattle

An experiment examined delta9 desaturase activity and FA composition in subcutaneous adipose tissue in two differing breeds of cattle. Jersey-sired cattle had significantly higher rates of desaturase activity than Limousin-sired cattle (1.55 vs. 0.75 nmol/mg protein/min). This difference was also demonstrated by a lower concentration of individual (e.g., 18:0) and total saturated FA (38.3 vs. 45.1 wt%), and a higher concentration of individual (e.g., 16:1) and total monounsaturated FA (58.2 vs. 52.7 wt%) in the Jersey animals. Other indices of desaturation calculated from the FA composition showed this same difference. The slip point of adipose tissue of Jersey cattle (36.8 degrees C) was significantly lower than that of Limousin cattle (39.2 degrees C), but Jersey adipose tissue had a greater content of beta-carotene. The positive relationship between adipose tissue beta-carotene and desaturation opposes the negative relationship between dietary beta-carotene and desaturation determined elsewhere. These results, however, lead to the hypothesis that some cattle have a reduced capacity to metabolize beta-carotene to various forms of vitamin A, a compound that can reduce delta9 desaturase enzyme activity. In addition, the higher level of intramuscular fat in Jersey cattle (6.97 vs. 3.82%) is possibly related to a lack of inhibition of the adipocyte differentiation genes by vitamin A.