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Double-muscled cattle are breeds of cattle that carry one of seven known mutations that limits and reduces the activity of the myostatin protein. Normally, myostatin limits the number of muscle fibers present at birth, and interfering with activity of this protein causes animals to be born with higher numbers of muscle fibers, consequently augmenting muscle growth.
Myostatin-related muscle hypertrophy is a rare genetic condition characterized by reduced body fat and increased skeletal muscle size. [1] Affected individuals have up to twice the usual amount of muscle mass in their bodies, but increases in muscle strength are not usually congruent. [ 2 ]
Myostatin is a myokine that is produced and released by myocytes and acts on muscle cells to inhibit muscle growth. [7] Myostatin is a secreted growth differentiation factor that is a member of the TGF beta protein family. [8] [9] Myostatin is assembled and produced in skeletal muscle before it is released into the blood stream. [10]
The active-myostatin gene acts as a "governor" on muscle growth; myostatin is a protein that instructs muscles to stop growing. In effect, when inactive, as it is with Piedmontese cattle, it no longer prevents muscle development which is what allows for the hypertrophic condition sometimes referred to as "double muscling". [7]
The Belgian Blue's bone structure is the same as normal cattle, albeit holding a greater amount of muscle, which causes them to have a greater meat to bone ratio. These cattle have a muscle yield around 20% more on average than cattle without the genetic myostatin mutation. [ 7 ]
In cattle, certain growth features are controlled by recessive genes which have not so far been controlled, complicating breeding. [11] One such trait is dwarfism; another is the doppelender or "double muscling" condition, which causes muscle hypertrophy and thereby increases the animal's commercial value. [11]
Studies of double-muscled cattle [49] [50] identified natural mutations of the myostatin gene which produce inactivated proteins that are unable to control muscle development. In Belgian Blue and Piedmontese cattle this causes an increase in muscle mass of 20–25%.
Due to their significant nutrition redistribution function, β-agonists have been applied in the livestock industry such as pigs and ruminants to reduce carcass fat and increase muscle mass while improving growth rate and feed conversion ratio (Bareille and Faverdin, 1996, Bergen et al., 1989, Byrem et al., 1998, Cardoso and Taveira, 2002 ...