Logan Steele
Double muscling in cattle, also known as myofibre hyperplasia, doppellender, muscular hypertrophy, a groppa doppia, and culard, is a condition that results in increased muscle mass and reduced fat deposits. This condition has been observed in many breeds of cattle and is caused by mutations in the myostatin gene, which plays a critical role in regulating skeletal muscle development. Animals with double muscling exhibit higher carcass yields and improved meat tenderness, but also face challenges such as increased susceptibility to respiratory diseases, urolithiasis, lameness, and heat stress. The management of double-muscled animals requires specialized husbandry practices and considerations to balance the benefits and drawbacks of this condition.
| Characteristics | Values |
|---|---|
| Cause | Mutations in the myostatin (MYO) gene |
| Type of mutation | nt821 allele (a deletion of 11 nucleotides in the coding DNA sequence at positions 821-831) |
| Other types of mutations | Q204X; nt419; E226X; C313Y and E291X |
| Breeds | Belgian Blue, Piedmontese, Parthenais, American Highland, Asturiana, Blonde d’ Aquitaine, Limousin, South Devon, Santa Gertrudis, Braford, Murray Grey, Angus, Charolais, Brown Swiss, Polled Hereford, Gelbvieh, Guernsey, Ayrshire, Brahman, Polled Shorthorn, and Texas Longhorn |
| Effect on meat | Lower collagen content, less marbling, lower fat content, healthier, more tender |
| Effect on animals | Smaller organ size, more pressure on the skeleton, lower robustness, increased susceptibility to respiratory disease, urolithiasis, lameness, muscle degeneration, heat stress, dystocia, nutritional stress, lower feed intake capacity, lower capillary density, more glycolytic metabolism |
| Inheritance | Autosomal recessive trait |
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What You'll Learn
Mutations in the myostatin gene
In 1997, the gene encoding myostatin was discovered, and laboratories soon identified mutations in the myostatin gene that led to an absence of functional myostatin. In cattle, this results in muscle cells multiplying rather than enlarging. The Belgian Blue breed is the most extensively studied double-muscled breed of cattle, and the double muscling phenotype is inherited as a single genetic locus designated muscular hypertrophy (mh). The mh mutation causes an average increase in muscle mass of 20-25% and a decrease in the mass of most other organs. Belgian Blue cattle exhibit the characteristic double muscling phenotype caused by the myostatin nt821 allele. The nt821 allele is a deletion of 11 nucleotides in the coding DNA sequence at positions 821-831, which causes the double muscling phenotype.
Within several cattle breeds, at least six versions of myostatin mutations have been identified: nt821 del 11, Q204X, nt419, E226X, C313Y, and E291X. Animals with one form of these genes are heterozygous, while those with two copies are homozygous and likely to exhibit double muscling characteristics. Homozygous individuals with mutations in both copies of the myostatin gene have significantly more muscle mass and are stronger than normal.
Double muscling in cattle has economic benefits, such as increased muscle mass, higher meat yield, and a higher proportion of expensive cuts of meat. However, it also has drawbacks, including increased susceptibility to dystocia, respiratory disease, lameness, muscle degeneration, and heat stress. DM animals may also be more susceptible to nutritional stress, urolithiasis, and reduced feed intake capacity, requiring a diet with greater nutrient density.
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Increased meatiness in beef cattle
The pursuit of increased meatiness in beef cattle has led to the development of double-muscled (DM) animals, characterised by the inactivation of the myostatin gene. This phenomenon, first observed by Darwin and later exploited in breeds like the Belgian Blue, has resulted in cattle with excellent conformation and high carcass yield, but also reduced organ mass and susceptibility to health issues.
Causes of Double Muscling
The primary cause of double muscling in beef cattle is attributed to mutations in the myostatin (MYO) gene, specifically the nt821 variant, which leads to muscle hypertrophy. The myostatin protein is crucial in regulating skeletal muscle development, and its dysfunction results in increased muscle mass. This condition has been recognised for over a century, but its prevalence increased after the Second World War due to advancements in veterinary medicine.
Impact on Meat Production
The selection for increased meatiness has led to DM animals with desirable traits for meat production, such as higher meat yield, leanness, and tenderness. Their carcasses have a lower collagen content, contributing to meat tenderness. Additionally, DM animals have improved feed efficiency, requiring less feed intake due to their reduced organ mass. However, they are more susceptible to respiratory diseases, stress, and dystocia, necessitating extra care for their welfare.
Strategies for Improvement
To optimise the benefits of double muscling while mitigating its drawbacks, several strategies can be employed:
- Genetic Testing and Selection: Breeders can test for the presence of the double-muscling allele to make informed decisions about their breeding programs.
- Nutritional Management: DM animals require a diet with greater nutrient density due to their reduced feed intake capacity.
- Slaughter Conditions: Appropriate slaughter techniques are necessary to maintain high meat quality, considering the unique metabolism and alterations in DM animals.
- Environmental Factors: Managing factors such as age, nutrition, and pre-slaughter conditions can influence meat quality, including colour, tenderness, and juiciness.
By addressing these considerations, producers can harness the economic advantages of double muscling while ensuring the health and welfare of their herds.
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Drawbacks of double muscling
Double muscling in cattle is caused by mutations in the myostatin gene, which increase muscle mass and reduce organ mass. While this can be advantageous for meat production, there are several drawbacks to double muscling that should be considered:
Susceptibility to Disease and Stress: Double-muscled animals have smaller hearts and lungs, which can lead to respiratory disease and increased stress susceptibility. They are also more prone to dystocia (calving difficulties), lameness, muscle degeneration, urolithiasis, and heat stress.
Nutritional Challenges: The reduced organ mass in double-muscled animals results in a lower feed intake capacity, requiring a diet with a greater nutrient density. This can be challenging to manage and may impact the animal's overall health and robustness.
Metabolic Issues: Double-muscled animals have a lower blood oxygen capacity, making them more susceptible to metabolic acidosis caused by exercise. They also experience faster post-mortem glycolysis, which can affect meat quality and yield.
Lower Robustness: The combination of increased muscle mass and weight in double-muscled calves can create calving difficulties, especially in homozygous cows with smaller pelvic sizes. This can result in a lower robustness and survival rate for both the cow and the calf during the birthing process.
Potential Financial Risks: While double muscling can offer financial rewards due to increased muscle volume, it also comes with potential financial risks. Double-muscled animals may be more challenging and less profitable for a herd, requiring specialized husbandry practices to realize their economic potential.
Overall, while double muscling can provide benefits in terms of meat production and economic value, it is important to consider the potential drawbacks and challenges associated with this condition to ensure the health and welfare of the animals and optimize meat quality.
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Myostatin variants
Myostatin is a protein that in humans is encoded by the MSTN gene. It is a myokine that is produced and released by myocytes and acts on muscle cells to inhibit muscle growth. Myostatin is assembled and produced in skeletal muscle before it is released into the blood stream.
Myostatin-related muscle hypertrophy is a rare genetic condition characterised by reduced body fat and increased skeletal muscle size. Individuals with this condition have up to twice the usual amount of muscle mass in their bodies. Myostatin-related muscle hypertrophy is not known to cause medical problems, and affected individuals are intellectually normal.
In cattle, mutations in the myostatin (MYO) gene result in muscle hypertrophy, which is characteristic of the phenotype known as double muscling. The myostatin protein is a critical regulator of skeletal muscle development. Genetic variants in the myostatin (MYO) gene can lead to a defective and dysfunctional protein, resulting in muscle hypertrophy. Several variants have been associated with double muscling in cattle, including the nt821 allele, which causes the double muscling phenotype in the Belgian Blue breed.
Double muscling in cattle has been reported for over a century, but it was only fully exploited after World War II due to the availability of anaesthesia, antibiotics, and new surgical methods. Belgian Blue cattle, for instance, exhibit the characteristic double muscling phenotype caused by the myostatin nt821 allele. Matings between two carriers are predicted to produce 25% of offspring with double muscling.
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Heterozygous and homozygous cattle
Double muscling in cattle is caused by mutations in the myostatin gene, which limit and reduce the activity of the myostatin protein. Myostatin, a member of the transforming growth factor β superfamily, is a secreted growth and differentiation factor that is essential for the proper regulation of skeletal muscle mass. Normally, myostatin 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.
The double-muscle trait is characterised by an increase in muscle mass of approximately 20%, resulting in a higher meat yield and a larger proportion of premium cuts of meat. This trait is inherited and is most prevalent in the Belgian Blue and Piedmontese breeds, although it occurs in other breeds as well. The Belgian Blue breed, for instance, was once divided into two strains, one for beef and the other for milk, but it is now primarily used for beef.
The condition can be observed in both heterozygous and homozygous cattle. Heterozygous calves with the double-muscled gene have been compared to normal calves in British breeds of cattle in terms of growth, food intake, and body composition. While heterozygous animals with one copy of the mh allele show some fibre increase, the level of heritability is low and subject to variability. Homozygous double-muscled animals, on the other hand, have two copies of the mutant myostatin gene, resulting in more pronounced effects. These animals have substantially enlarged muscles, reduced body fat proportion, and thinner skin. They also exhibit improved meat tenderness in some cuts of meat.
The advantages of double muscling, particularly in homozygous cattle, have led to their widespread use in animal agriculture in several countries. However, there are also drawbacks to this condition. Double-muscled cattle experience calving difficulties, with a higher likelihood of requiring birth by caesarean section. Additionally, they are more susceptible to respiratory disease, stress, and dystocia, necessitating extra care for their welfare.
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Frequently asked questions
Double muscling is a condition in cattle where they carry one of seven known mutations that limit and reduce the activity of the myostatin protein, leading to increased muscle growth.
The double muscling condition is caused by mutations in the myostatin (MYO) gene, which result in a defective and dysfunctional protein. This leads to muscle hypertrophy, or increased muscle mass, in the affected animals.
The double muscling condition has various effects on cattle, including increased muscle mass, higher meat yield, improved meat tenderness, and lower fat content. However, it can also lead to smaller organ size, additional pressure on the skeleton, and increased susceptibility to certain health issues such as respiratory disease, lameness, and heat stress.
The Belgian Blue, Piedmontese, and Parthenaise cattle breeds are commonly affected by the double muscling condition. Other breeds that possess the double muscle gene include the American Highland, Asturiana, Blonde d’ Aquitaine, Limousin, South Devon, and Angus.
