Myostatin, also known as GDF8 (growth differentiation factor 8), belongs to one of the biggest groups of proteins, called transforming growth factors (TGF-β). The protein regulates embryonic development and maintains homeostasis of full-grown individuals. When the process of maturation is over, GDF8 becomes a negative regulator of skeletal muscle growth. The physiological role of myostatin is to prevent overgrowth of muscle tissue in various stages of organism development. It also inhibits the regeneration of skeletal muscles by weakening activation and proliferation of satellite cells and the migration of macrophages and myoblasts to the site of injury. Several mutations within the sequence of MSTN have been described; they may affect the activity of the protein in the tissues, and hence the level of the functional characteristics of the animals, which determine the value of breeding animals. Understanding the impact of individual mutations in the gene encoding the protein is particularly important in relation to production traits of livestock.