Double-Muscled Cattle Breeds
The Belgian Blue, Piedmontese and Parthenais
Double muscling in cattle produces an 'incredible hulk' type outline with exaggerated muscle growth creating animals with a sculpted, massive appearance. Double muscling (also called muscular hypertrophy) is an inherited condition, characterised by an increase in number and, to a lesser degree, an enlargement of the muscle fibres.
This double muscling is caused by a mutation which suppresses the protein element, myostatin with a consequent augmentation of muscle growth.
Myostatin is one of a group of factors essential for proper regulation of skeletal muscle mass. Mutations in the coding sequence result in an increase in muscle mass. Only a few cattle breeds are affected by this mutation. The Belgian Blue, Piedmontese and Parthenais all exhibit double muscling to a degree.
Animals with the condition may have an increase in muscle mass of about 20%. This increase in the number of muscle fibres occurs in the uterus with affected animals exhibiting nearly double the number of muscle fibres at birth. Another characteristic is the significantly reduced amount of connective tissue or collagen. The collagen that is present is structurally different. Muscle development is not consistent throughout the animal. There is minimal development round the neck but an increase towards the hindquarters with maximum development appearing in the hindquarters. Thus double muscling results in a higher proportion of the more desirable cuts of meat in a carcass as opposed to the carcass of cattle without double muscling.
Bone mass tends to be around 10% less due to the long bones being shorter, more slender and less dense resulting in a significantly higher muscle to bone ratio.
Double-muscled cattle have a lower fat content in fatty tissues. The volume of fat cells is reduced rather than the number of fat cells. As well, the fat composition is different with a much higher percentage of polyunsaturated fats. Normal cattle may have 5% of polyunsaturated fats compared to 11% in double-muscled cattle. Carcasses dress out at between 65 and 70%. Meat is more tender (possibly due to collagen content) and more lean which is what consumers like.
On the down side, double-muscled cattle have a reduced tolerance for heat stress and become fatigued more quickly when undergoing forced activity. The condition is also associated with problems with reproduction especially where the syndrome is fully present. There may be delays in puberty, reduced fertility, increased problems calving, reduced milk production and increased calf mortality.
Higher birth weights and higher pre-weaning growth rates are usual. Following weaning, growth rates tend to fall behind other breeds, possibly due to a lower feed intake.
The Belgian Blue exhibits a high degree of double muscling with carcasses dressing out in excess of 80%. The breed carries two copies of the gene which causes the mutation. Crossbreds generally inherent one gene which still results in an increased carcass weight.
The Piedmontese is a breed of cattle from the Piedmont region in north-west Italy. Development was by natural selection followed by normal husbandry practices until the late 19th century which double muscling first appeared. The Piedmontese was then selectively bred for the factor.
The Parthenais beef breed is from the Deux-Sevres region of western France. They have been selectively bred since 1970 as a pure beef breed and show a degree of double muscling although not to the same degree as the Belgian Blue.