301. Vitamin A–mediated Developmental Programming of Muscle and Marbling Fat in Beef Cattle.

Abstract Intramuscular fat (IMF), or marbling, is a key determinant of beef quality, whereas muscle growth underlies meat production efficiency. During embryonic development, muscle cells, adipocytes, and fibroblasts arise from a common pool of mesenchymal progenitors. In early embryos, a subset of progenitor cells within the muscle anlage commits to the myogenic lineage, while the remaining non-myogenic cells differentiate into adipo-fibrogenic or other cell types. Myogenic cells proliferate extensively and give rise to primary and secondary muscle fibers as well as satellite cells. In contrast, adipo-fibrogenic cells contribute to the stromal-vascular fraction of muscle, which harbors intramuscular adipocytes and fibroblasts. Enhancing prenatal myogenesis promotes lean growth potential, whereas stimulating intramuscular adipocyte formation establishes the cellular foundation for marbling deposition during the finishing stage. Notably, intramuscular adipocytes develop later than subcutaneous, visceral, and intermuscular fat depots, and this difference in developmental timing provides an opportunity for targeted nutritional intervention to enhance marbling. Vitamin A regulates cell proliferation and differentiation through its active metabolite, retinoic acid. Emerging evidence suggests that vitamin A supplementation during late gestation and the neonatal period promotes both myogenesis and the formation of intramuscular adipocytes in beef cattle. Conversely, because vitamin A enhances lipid oxidation, its restriction during the finishing stage increases IMF deposition and raises the proportion of prime-grade carcasses. In summary, stage-specific vitamin A management represents an effective strategy to optimize muscle development and maximize IMF deposition, thereby improving both beef production efficiency and meat quality.