Dominic Stone
Double-muscled cattle are breeds of cattle that carry one of seven known mutations that limit and reduce the activity of the myostatin protein, which normally limits the number of muscle fibres present at birth. This interference with the myostatin protein causes animals to be born with higher numbers of muscle fibres, increasing muscle growth. This results in more meat for cattle farmers, but it also causes a number of problems for the cattle, including reduced organ mass, increased susceptibility to respiratory disease, stress, and dystocia.
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What You'll Learn
Mutations and the myostatin gene
Double-muscled cattle are breeds of cattle that carry one of seven known mutations that limit and reduce the activity of the myostatin protein. Myostatin is a growth differentiation factor that normally limits the number of muscle fibres present at birth. Interfering with the activity of this protein causes animals to be born with higher numbers of muscle fibres, increasing muscle growth.
The Belgian Blue breed is a typical example of the exploitation of the myostatin gene. The Belgian Blue was established in the early 20th century and is now primarily used for beef. The Belgian Blue myostatin sequence contains an 11-nucleotide deletion in the third exon, which causes a frameshift that eliminates almost all of the mature, active region of the molecule. This results in an average increase in muscle mass of 20-25% and a decrease in the mass of most other organs.
The Piedmontese breed, discovered in Italy in 1897, also has a mutation in the third exon, which changes a cysteine to a tyrosine in the same highly conserved region of the gene. This results in a similar increase in muscle mass relative to conventional cattle. The Parthenaise, found in France in 1893, is another breed that possesses the double-muscle gene.
The muscular hypertrophy phenotype has also been observed in a single human child, who possessed two copies of a G-to-A transition in the noncoding region of the human MSTN gene. This mutation resulted in the mis-splicing of precursor mRNA, which most likely truncated the myostatin protein. The child's mother, a former professional athlete, was heterozygous for this mutation and also appeared muscular, although not to the same degree as her child.
Double muscling has also been observed in other mammalian species, including sheep and whippet dogs. Dogs that possess a single copy of the mutation are more muscled than normal, while dogs with two copies of the same mutation are grossly overmuscled, resembling double-muscled cattle.
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Advantages and disadvantages
Double-muscled cattle are breeds of cattle that carry a mutation that limits and reduces the activity of the myostatin protein. This protein normally limits the number of muscle fibres present at birth, but when its activity is disrupted, animals are born with higher numbers of muscle fibres, leading to augmented muscle growth. This results in more meat for cattle farmers.
Advantages
Double-muscled cattle have a number of advantages, including:
- More meat yield: The increased muscle mass in double-muscled cattle results in a higher carcass yield, providing more meat for farmers.
- Leaner meat: Double-muscled cattle have reduced fat deposits, resulting in meat that is lower in fat content and higher in tenderness.
- Improved feed efficiency: Despite a reduced feed intake, double-muscled cattle have improved feed efficiency due to their lower organ mass.
- Crossbreeding advantages: Crossbreeding double-muscled cattle with other breeds can result in offspring with accelerated growth, improved weight gain, and higher live weight, leading to significant financial advantages for farmers.
Disadvantages
However, there are also several disadvantages to double-muscled cattle:
- Health issues: Double-muscled cattle are more susceptible to respiratory disease, urolithiasis, lameness, nutritional stress, heat stress, and dystocia due to their smaller organs and lower respiratory capacity.
- Difficult calving: The enlarged muscles of dam and calf can lead to a difficult calving process, with some breeds requiring a higher likelihood of birth by cesarean section.
- Negative impact on reproduction: The double-muscling trait can have deleterious effects on the male and female reproductive systems, impacting fertility and breeding success.
- Sensitivity to stress: Double-muscled cattle are more prone to stress due to their smaller heart and lungs, lower blood oxygen capacity, and higher susceptibility to metabolic acidosis.
- Quality of meat: While double-muscled cattle produce leaner meat, the quality of the meat may be inconsistent, with potential issues such as dark cutting conditions and reduced meat tenderness, colour, and juiciness.
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Identification and testing
Double-muscled cattle are breeds of cattle that carry one of seven known mutations that limit and reduce the activity of the myostatin protein. Myostatin usually limits the number of muscle fibres present at birth, but when its activity is disrupted, animals are born with higher numbers of muscle fibres, leading to augmented muscle growth. This also reduces fat deposits, resulting in meat that is less marbled and lower in fat content.
Double muscling in cattle has been reported for over a century, but it was only after the Second World War that it became more common, thanks to the availability of anaesthesia, antibiotics, and new surgical methods that made caesarean operations more viable.
Breeds such as the Belgian Blue, Piedmontese, Parthenaise, Angus, and South Devon frequently display double muscling. However, double muscling can be expressed in many other breeds as well.
Double muscling is a genetic syndrome caused by a mutation of the myostatin gene. As a genetic condition, it is possible to test for the presence of the myostatin gene. Many breed societies offer testing for producers and breeders so they can make more strategic choices when selecting bulls and avoid increasing the risk of animals possessing two copies of the gene.
Breeders should consider gene testing to provide their clients with as much information as possible to assist in making decisions for their herds. This is especially important when there is a desire to increase muscling across the herd. Testing is also useful for managing the risks of double muscling within a herd. While carrier animals may offer advantages, it is best to have full knowledge of the animal and the limitations associated with future breeding decisions.
Tests can identify heterozygous animals (those with one form of the gene) and homozygous animals (those with two copies of the gene). Homozygous animals are likely to exhibit double-muscling characteristics, such as a smaller skeleton, greater angularity of the hip bone, and a narrower pelvic opening. These traits can dramatically reduce calving ease and increase the likelihood of birth by caesarean section.
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Meat quality and yield
Double-muscled cattle are characterised by an excellent conformation and an extremely high carcass yield, coinciding with a reduced organ mass. The inactivation of the myostatin gene in these animals leads to a significant increase in muscle mass and reduced fat deposits, resulting in leaner meat with improved tenderness.
The Belgian Blue breed, originating from Belgium, is a prominent example of double-muscled cattle, showcasing the impact of the myostatin gene. This breed was once divided into two strains, one focused on beef and the other on milk production. Today, the Belgian Blue is primarily renowned for its beef, gaining recognition from breeders worldwide.
The high carcass yield in double-muscled animals is accompanied by a decrease in the size of vital organs. This trait leads to a reduction in feed intake capacity, necessitating a nutrient-dense diet to meet their requirements. Additionally, these animals are more susceptible to certain health issues, such as respiratory disease, urolithiasis, lameness, nutritional stress, heat stress, and dystocia. As a result, they require extra care and attention regarding their accommodation and welfare.
The meat produced from double-muscled cattle exhibits notable differences in its fatty acid profile compared to non-DM animals. It contains lower levels of saturated fatty acids and overall fat content. The collagen content is also reduced, contributing to the improved tenderness of the meat. These factors collectively influence the meat quality and yield, making double-muscled cattle a subject of interest for meat production.
Furthermore, the impact of double muscling on meat quality and yield extends beyond the characteristics of the meat itself. The increased muscle mass and reduced fat deposits result in a higher lean meat content in the carcass. For example, when comparing Belgian Blue bulls with and without the DM genotype, the DM animals yielded 28% more total meat. This increase in lean meat content translates to a higher proportion of higher-priced roasts and steaks, enhancing the economic value of the meat produced from double-muscled cattle.
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Muscular hypertrophy
Double-muscled cattle are breeds of cattle that carry one of seven known mutations that limit and reduce the activity of the myostatin protein. Myostatin is a hormone that controls muscle growth by limiting the number of muscle fibres present at birth. Interfering with the activity of this protein causes animals to be born with a higher number of muscle fibres, resulting in augmented muscle growth. This is known as muscular hypertrophy.
The muscular hypertrophy of double-muscled cattle is identified by visual assessment of the degree of muscular hypertrophy, looking at protruding muscles and intermuscular grooves under the skin. This method is only accurate in classifying normal and homozygous double-muscled animals, but it does not allow for the distinction of heterozygous animals.
Breeders are interested in double-muscled cattle because studies have shown that the meat quality (assessed by tenderness, ease of fragmentation, and amount of connective tissue) was better in carcasses with at least one defective myostatin gene than in carcasses with two normal myostatin genes. The meat on double-muscled cattle is more valuable to consumers and producers, which may drive producers to breed for double muscling.
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Frequently asked questions
Double-muscled cattle are breeds of cattle that carry one of seven known mutations that limit and reduce the activity of the myostatin protein. Myostatin usually limits the number of muscle fibres present at birth, but when its activity is disrupted, animals are born with more muscle fibres, resulting in increased muscle growth.
Double-muscled cattle yield more meat and less fat. The meat is also more tender and valuable to consumers and producers.
The Belgian Blue, Piedmontese, Parthenaise, and Texel breeds are all associated with double muscling.
Double-muscled animals can be identified by visual assessment of their protruding muscles and intermuscular grooves under the skin. Gene testing can also be used to identify carriers of the myostatin mutation.
