Myostatin (also known as growth differentiation factor 8, abbreviated GDF-8) is a protein that in humans is encoded by the MSTN gene. Myostatin is a secreted growth differentiation factor that is a member of the TGF beta protein family that inhibits muscle differentiation and growth. Myostatin is produced primarily in skeletal muscle cells, circulates in the blood and acts on muscle tissue, by binding a cell-bound receptor called the activin type II receptor.
Animals lacking myostatin or animals treated with substances such as follistatin that block the binding of myostatin to its receptor have significantly larger muscles. Thus, reduction of myostatin could potentially benefit the livestock industry, with even a 20 percent reduction in myostatin levels potentially having a large effect on the development of muscles.
However, the animal breeds developed as homozygous for myostatin deficiency have reproduction issues due to their unusually heavy and bulky offspring, and require special care and a more expensive diet to achieve a superior yield. This negatively affects economics of myostatin-deficient breeds to the point where they do not usually offer an obvious advantage. While e.g. Piedmontese beef has a place on the specialist market due to its unusual properties, at least for purebred myostatin-deficient strains the expenses and (especially in cattle) necessity of veterinary supervision place them at a disadvantage in the bulk market.
Read more about Myostatin: Discovery and Sequencing, Effects of Inactivated Myostatin in Cattle, Double-muscle Mutation in Humans, Performance Enhancement in Dogs, Biochemistry, Clinical Research, Gene Doping