The Physiology of marbling: What is it, and why does it develop

This review describes our current understanding of the factors affecting growth and development of adipocytes in bovine skeletal muscle and discusses alternative hypotheses to explain intramuscular fat deposition: marbling. While genetic predisposition clearly plays a role in the development of this commercially interesting phenotype, animal age, energy nutrition, vitamin nutrition, compensatory growth and previous growth rate may also contribute to the final outcome. The review briefly analyses the data supporting each hypothesis and attempts a mechanistic description based on the development of tissue precursor cells into mature adipocytes. Properties of the mature adipocyte in the context of whole animal and muscle biochemistry are discussed in the companion paper by Pethick et al. (2001).