Intramuscular fat (IMF) content in skeletal muscle including the longissimus dorsi muscle (LM), also known as marbling fat, is one of the most important factors determining beef quality in several countries including Korea, Japan, Australia, and the United States. Genetics and breed, management, and nutrition affect IMF deposition. Japanese Black cattle breed has the highest IMF content in the world, and Korean cattle (also called Hanwoo) the second highest. Here, we review results of research on genetic factors (breed and sex differences and heritability) that affect IMF deposition. Cattle management factors are also important for IMF deposition. Castration of bulls increases IMF deposition in most cattle breeds. The effects of several management factors, including weaning age, castration, slaughter weight and age, and environmental conditions on IMF deposition are also reviewed. Nutritional factors, including fat metabolism, digestion and absorption of feed, glucose/starch availability, and vitamin A, D, and C levels are important for IMF deposition. Manipulating IMF deposition through developmental programming via metabolic imprinting is a recently proposed nutritional method to change potential IMF deposition during the fetal and neonatal periods in rodents and domestic animals. Application of fetal nutritional programming to increase IMF deposition of progeny in later life is reviewed. The coordination of several factors affects IMF deposition. Thus, a combination of several strategies may be needed to manipulate IMF deposition, depending on the consumer’s beef preference. In particular, stage-specific feeding programs with concentrate-based diets developed by Japan and Korea are described in this article.

Intramuscular fat (IMF) in cattle is an important component of traits that influence meat quality. We measured carcass characteristics and gene expression in Korean steers to clarify the molecular mechanism(s) underlying IMF deposition in LM tissue by determining the correlation between IMF content and gene expression abundance and by developing models to predict IMF content using gene expression abundance. The deposition of IMF is determined by a balance between fat deposition and fat removal in the LM. We measured mRNA abundance of lipid metabolic genes including lipogenesis [acetyl CoA carboxylase (ACC), fatty acid synthase (FASN)], fatty lipid uptake [lipoprotein lipase (LPL), fatty acid translocase (CD36), fatty acid transport protein 1 (FATP1)], fatty acid esterification [glycerol-3-phosphate acyltransferase 1 (GPAT1), acylglycerol phosphate acyltransferase 1 (AGPAT1), diacylglycerol acyltransferase 1 (DGAT1), DGAT2], lipolysis [adipose triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), monoglyceride lipase (MGL)], and fatty acid oxidation [carnitine palmitoyl transferase 1B, very long-chain acyl-CoA dehydrogenase (VLCAD), medium-chain acyl-CoA dehydrogenase (MCAD)] in the LM. The mRNA abundance of the GPAT1 gene showed the greatest correlation (r = 0.74; P < 0.001) with IMF content among 9 fat deposition genes. The gene expression abundance of other fat deposition genes including ACC, FASN, LPL, CD36, FATP1, AGPAT1, DGAT1, and DGAT2 also exhibited significant positive correlations (P < 0.05) with IMF content in the LM. Conversely, ATGL mRNA abundance showed the greatest negative correlation (r = -0.68; P < 0.001) with IMF content in the LM among 6 fat removal genes. The expression of other fat removal genes including MGL, VLCAD, and MCAD showed significant negative correlations (P < 0.05) with IMF content. Our findings show that the combined effects of increases in lipogenesis, fatty acid uptake, fatty acid esterification, and of decreases in lipolysis and fatty acid oxidation contribute to increasing IMF deposition in Korean steers. The multiple regression analysis revealed that the mRNA abundance of the GPAT1 gene in the LM was the first major variable predicting IMF content (54%) among 15 lipid metabolic genes. The second was mRNA abundance of ATGL (11%). In conclusion, these results suggest that GPAT1 and ATGL genes could be used as genetic markers to predict IMF deposition in the LM.

The liver is a primary target of growth hormone (GH). GH signals are mediated by the transcription factor signal transducer and activator of transcription 5 (STAT5). Here, we focus on recent discoveries about the role of GH-STAT5 signaling in hepatic physiology and pathophysiology. We discuss roles of the GH-STAT5 axis in body growth, lipid metabolism, and the cell cycle pertaining to hepatosteatosis, fibrosis, and hepatocellular carcinoma. Finally, we discuss recent discoveries about the role of GH-STAT5 in sex-specific gene expression and bile acid, steroid, and drug metabolism.

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Castration increases intramuscular fat (IMF) deposition, improving beef quality in cattle. The present study was performed to determine the global transcriptome changes following castration of bulls and to identify genes associated with IMF deposition in the longissimus dorsi (LM) of Korean cattle. A customized bovine CombiMatrix oligonucleotide microarray was constructed, and transcriptome changes following castration were determined by microarray hybridization. Transcriptome comparison between bulls and steers indicated that 428 of 8,407 genes were differentially expressed in the LM by greater than two fold (P < 0.05). Gene expression profiling indicated alterations in several pathways, including adipogenesis, fatty acid oxidation, tricarboxylic acid (TCA) cycle, and oxidative phosphorylation (OP), following castration. Castration upregulated transcription of adipogenic perilipin 2 (PLIN2) and visfatin, lipogenic fatty acid synthase, fatty acid esterification 1-acylglycerol-3-phosphate O-acyltransferase 5, and many fatty acid oxidation-related genes. Many TCA cycle and OP genes were also transcriptionally upregulated. Correlation analysis indicated that the IMF content in the LM was highly correlated with mRNA levels of PLIN2 (r = 0.70, P < 0.001), adenosine triphosphatase (ATPase), H(+)-transporting, lysosomal 42 kDa, V1 subunit C1 (ATP6V1C1: r = 0.66, P < 0.001), and cytochrome c oxidase assembly homolog 11 (COX11: r = 0.72, P < 0.001) genes in a pooled animal group of steers plus bulls, and significant correlations in the steer-alone group were maintained in the 3 genes, PLIN2 (r = 0.47, P < 0.05), ATP6V1C1 (r = 0.50, P < 0.05), and COX11 (r = 0.60, P < 0.01). In conclusion, our study provided evidence that castration shifts transcription of lipid metabolism genes, favoring IMF deposition by increasing adipogenesis, lipogenesis, and triglyceride synthesis. This study also indicated that castration increases transcription of genes involved in fatty acid oxidation and subsequent energy production (TCA and OP genes). Our microarray analysis provided novel information that castration alters the transcriptome associated with lipid/energy metabolism, favoring IMF deposition in the LM.