A novel SNP was discovered within the promoter region of alcohol dehydrogenase 1C (ADH1C c.-64T>C), the C allele eliminating a potential binding site for the transcription factor C/EPBα. The purpose of this study was to examine if an interaction between this SNP and vitamin A restriction had an effect on carcass characteristics in beef cattle. Following backgrounding on a β-carotene-defi cient diet, 130 steers (50 TT, 50 CT, and 30 CC) were fi nished for 5 mo and received either no supplemental

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... vitamin A (unsupplemented) or 750,000 IU/mo (supplemented). A subgroup of 5 steers•genotype −1 •treatment −1 was randomly selected for pre-and postfi nishing liver biopsies to assess vitamin A status and measure gene expression. Unsupplemented steers (Bos taurus) had signifi cantly greater (P < 0.05) marbling scores than supplemented steers. There was a signifi cant interaction between genotype and vitamin A supplementation on ether-extractable intramuscular fat (IMF). Within the unsupplemented treatment, TT steers had nearly 23% greater IMF than CC steers. Additionally, unsupplemented TT steers had over 24% greater IMF than supplemented TT steers. Expression of ADH1C in the liver was additive with each additional T allele, potentially due to the elimination of a possible binding site for C/EBPα. It is plausible that CC cattle have reduced ability to metabolize retinol to retinaldehyde (and subsequently retinoic acid) and that a phenotypic effect is only observed when vitamin A is limiting. Therefore, ADH1C c.-64T>C genotype, in combination with reduced vitamin A supplementation, could potentially be implemented in marker-assisted management to maximize marbling in fi nishing cattle.