Deposition of intramuscular fat, or "marbling," in beef cattlecontributes significantly to meat quality variables, includingjuiciness, flavor, and tenderness. The accumulation of intramuscularfat is largely influenced by the genetic background of cattle,as well as their age and nutrition. To identify genes that canbe used as early biomarkers for the prediction of marbling capacity,we studied the muscle transcriptome of 2 cattle crossbreedswith contrasting intramuscular fat content. The transcriptomesof marbling LM tissue of heifers from Wagyu x Hereford (WxH;n = 6) and Piedmontese x Hereford (PxH; n = 7) crosses wereprofiled by using a combination of complementary DNA microarrayand quantitative reverse transcription-PCR. Five biopsies ofLM were taken from each animal at approximately 3, 7, 12, 20,and 25 mo from birth. Tissue was also collected from the LMof each animal at slaughter (approximately 30 mo). Microarrayexperiments, conducted on the first 3 biopsies of 2 animalsfrom each crossbreed, identified 97 differentially expressedgenes. The gene expression results indicated that the LM transcriptomeof animals with high marbling potential (WxH) could be reliablydistinguished from less marbled animals (PxH) when the animalswere as young as 7 mo of age. At this early age, one cannotreliably determine meaningful differences in intramuscular fatdeposition. We observed greater expression of a set of adipogenesis-and lipogenesis-related genes in the LM of young WxH animalscompared with their PxH contemporaries. In contrast, genes highlyexpressed in PxH animals were associated with mitochondrialoxidative activity. Further quantitative reverse transcription-PCRexperiments revealed that the messenger RNA of 6 of the lipogenesis-relatedgenes also peaked at the age of 20 to 25 mo in WxH animals.The messenger RNA expression of ADIPOQ, SCD, and THRSP was highlycorrelated with intramuscular fat content of an individual inWxH animals. Our study provides clear evidence of early molecularchanges associated with marbling and also identifies specifictime frames when intramuscular fat development in cattle musclecan be detected by using gene expression. This information couldbe used by animal scientists to design optimal nutrition forhigh marbling potential. In addition, the genes found to behighly expressed during development of marbling could be usedto develop genetic markers or biomarkers to assist with beefproduction strategies.