Myostatin (Growth differentiation factor 8) is often mislabeled a gene, but is actually a protein that is produced and released by myocytes that act on muscle cells’ autocrine function to inhibit “myogenesis” (muscle cell growth and differentiation). The gene involved is on Chromosome 2.
Lack of myostatin production is going to result in a significant increase in muscle mass. In beef cattle there are several “double muscled” breeds (or bloodlines within breeds) that involve this lack of what is considered “normal” myostatin production.
Breeds exhibiting some to all “double muscling”
Charolais (France) Gelbveih (Germany) Belgian Blue (England) Piedmontese (Italy)
Limousin (France) Fleckveih (Germany)
Maine Anjou (France)
Lack of myostatin (GDF-8) can be a mixed blessing of more edible muscle mass, but a more difficult calving for females, more difficult mounting and mobility for males. It is for various reasons such as these that the majority of Belgian Blue cattle (male or female) are raised for slaughter rather than for breeding, where a majority of births require caesarian section.
Piedmontese breeders have been proactive in screening females on the basis of ultrasound measurement of the pelvis before being added to a breeding herd. It is interesting that while some breeds show this double-muscling effect in each calf at birth, other breeds (such as Pied’s) are a few months old before the double-muscling effect is exhibited, allowing for more natural vaginal calf delivery.
The more extreme of double-muscling breeds have as a result of genetic selection also combined this trait with a smaller bone mass, and it is not unusual to see a 5% to almost 10% increase in percentage of
Edible carcass compared to traditional breed cattle.