The objective of this study was to compare the transcriptional profiles in adipose tissue of steers fed diets supplemented with Aspergillus oryzae (Amaize, Alltech Inc.). Angus-cross steers were randomly assigned to one of 3 treatments (n = 9/treatment): basal diet (CON, control), basal diet plus 10g/hd/d of A. oryzae introduced gradually during the transition phase (GRAD, gradual), or basal diet plus 10g/hd/d of A. oryzae introduced at full level at the end of the transition phase (FULL). For the GRAD treatment, A. oryzae was added gradually to the ration by increasing the dose 2.5 g every 3 d until steers were receiving 10g/d at d 19. From receiving until d 21, starter and step-up diets were fed to transition steers to a low-forage finishing ration. On d 140, adipose tissue was biopsied. Samples were analyzed for gene expression using the Affymetrix Bovine Genome Array. Performance did not differ between treatment groups, however GRAD and FULL steers had numerically greater hot carcass weights (P = 0.54) and rib eye areas (P = 0.15) than CON steers. Relative to CON, there were 930 (396 upregulated, 534 downregulated) differentially expressed genes (DEG) in FULL steers and 425 (196 upregulated, 229 downregulated) DEG in GRAD steers. In FULL steers, DEG categorized to both the oxidative phosphorylation and mitochondrial dysfunction pathways were downregulated, suggesting a decrease in cellular energy production. Key DEG included components of complex I, III, and IV and the ATP synthase subunits. Surprisingly, these pathways were unaffected in GRAD steers. Although performance or carcass characteristics did not differ (P < 0.05) between treatment groups, the DEG suggest that, at least in FULL steers, energy production may be decreased. A future study is warranted to examine response to Amaize in terms of steer carcass composition and transcriptional patterns in skeletal muscle.