A cow born without the protein Myostatin which allowed for unrestricted muscle growth

 

Belgian Blue is a breed of beef cattle from Belgium. These cattle are referred to in French as Race de la Moyenne et Haute Belgique, or, more commonly, Blanc Bleu Belge. Alternative names for this breed include Belgian Blue-White; Belgian White and Blue Pied; Belgian White Blue; Blue; and Blue Belgian. The Belgian Blue's sculpted, heavily muscled appearance is known as "double-muscling". The double-muscling phenotype is a heritable condition which results in the increased number of muscle fibers (hyperplasia) rather than the normal enlargement of individual muscle fibers (hypertrophy).

This particular trait is shared with another breed of cattle known as Piedmontese. Both of these breeds have an increased ability to convert feed into lean muscle, which causes these particular breeds' meat to have a reduced fat content. The Belgian Blue is named after their typically blue-grey mottled hair colour, however its colour can vary from white to black.

The condition was first documented in 1808 by a livestock observationist named George Culley.^[The breed originated in central and upper Belgium in the nineteenth century, from crossing local breeds with a Shorthorn breed of cattle from the United Kingdom. It is also possible that Charolais cattle were cross bred as well. Belgian Blue cattle were first used as a dairy and beef breed. The modern beef breed was developed in the 1950s by Professor Hanset, working at an artificial insemination center in Liege province. The breed's characteristic gene mutation was maintained through line breeding to the point where the condition was a fixed property in the Belgian Blue breed.

The Belgian Blue has a natural mutation in the myostatin gene which codes for the protein, myostatin ("myo" meaning muscle and "statin" meaning stop). Myostatin is a protein that acts to inhibit muscle development. This mutation also interferes with fat deposition, resulting in very lean meat. The truncated myostatin gene is unable to function in its normal capacity, resulting in accelerated lean muscle growth. Muscle growth is due primarily to physiological changes in the animal's muscle cells (fibers) from hypertrophy to a hyperplasia mode of growth. This particular type of growth is seen early in the fetus of a pregnant dam, which results in a calf that is born with two times the number of muscle fibers at birth than a calf with no myostatin gene mutation. In addition a new born double-muscled calf’s birth weight compared to a normal calf is significantly greater.

Belgian Blue cattle have improved feed conversion ratio (FCR) due to lower feed intake compared to weight gain. The ability for these animals to have improved FCR is due to an altered composition of body weight gain which includes increased protein and decreased fat deposition. The Belgian Blue’s bone structure is the same as a normal cow, albeit holding a greater amount of muscle, which causes them to have a greater meat to bone ratio. These cattle have a muscle yield of about 20% more on average than cattle without the genetic myostatin mutation. Because of this breed’s increased muscle yield a diet containing higher protein is required to compensate for the altered mode of weight gain. During finishing this breed requires high-energy (concentrated) feeds, and will not yield the same results if put on a high-fiber diet.

The value of the double-muscling breed is due to their superior carcass characteristics. However with decreased fat content there is decreased marbling of meat, which means the meat tenderness is reduced. Conversely, the Belgian Blue's meat tenderness has been argued to be just as tender because there are a large number of smaller muscle fibers. The Belgian Blue's meat cuts also have a lower collagen content, which allows the protein quality to be improved due to a higher yield of amino acids.