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BEEF SPECIAL: Myostatin in cattle - a veterinary perspective

Although calving is in full swing, thoughts will soon turn to calving 2022 with many new stock bulls bought in preparation. Knowing the myostatin status of a potential purchase is important as veterinary surgeon, Kaz Strycharczyk at Black Sheep Animal Health, Rothbury, explains.

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BEEF SPECIAL: Myostatin in cattle - a veterinary perspective

The criteria for bull selection are many and varied – conformation, character, pedigree, breed, estimated breeding values, temperament and more.

 

Kaz Strycharczyk says: “Farming is a fine balance, with trade-offs around every corner. Focusing excessively on one aspect is probably unwise.


“Therefore, the more information we can integrate into bull selection, the better.

 

“As genomic technology, which allows us to look at individual genes, becomes more accessible, more and more pedigree cattle are being genotyped for certain genes. One of these genes is known as myostatin and knowing the status of a potential stock bull is a vital piece of information.”

 

DNA is the genetic code of an animal. This code is made up of short sequences – genes – which act as individual blueprints for proteins.

 

Within animal cells, for proteins to be made, or ‘expressed’, the cell must first make a copy of this blueprint, which is then processed to make the corresponding protein.

 

Myostatin is one of these proteins. The role of proteins is hugely important and diverse.

 

Myostatin (myo- meaning muscle, -statin meaning to stop) regulates muscle growth.

 

From an evolutionary standpoint, muscle is a very expensive tissue to make and maintain as it uses a lot of energy. Hence, myostatin caps muscle growth within sensible limits, so energy can be saved for other tissues and functions such as fat, immune cells and reproductive organs.

 

Traits

 

Mr Strycharczyk says: “We all have myostatin – and we have two copies of the genes that encode it – one from our sire and one from our dam.

 

“Most traits are determined by very many different genes, each with a small influence on the end result. This applies for growth and conformation; it is just that myostatin seems to wield disproportionate influence for a single gene.

 

“If genes are codes, sometimes errors can be introduced when animals reproduce. Errors are random and typically lead to proteins working less well. If you swapped out one word randomly in a sentence, for example, it would be more likely to become nonsense than improve meaning of the sentence.

 

“When mutations occur in myostatin, they lead to copies that work less well, meaning more muscle growth. Strongman, Eddie Hall has stated in an interview that his own genetic analysis revealed he carries a myostatin variant.”


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There are several different mutations, or variants, of myostatin identified. Certain variants are associated with certain breeds. Mutations are not limited to continental breeds.

 

They are common in the Beef Shorthorn, Aberdeen-Angus and South Devon among others.

 

As an animal has two copies of the gene for myostatin, it can have two mutant versions, one mutant and one

normal, or two normal.

 

It is generally accepted that the changes seen are more extreme when an animal has mutations on both of its genes. What a calf ends up with is partly down to chance and partly down to parental status (see table).

 

“The potential benefit of this dysregulated muscle growth is that calves end up with a more extreme ‘beefy’ conformation.

 

“The EUROP grid, rightly or wrongly, rewards producers by conformation, so many producers aim for this style of calf. Of course, farmers are paid just as much by the number of calves sold, as well as their conformation, says Mr Strycharczyk.

 

“On the other hand, myostatin variants have been associated with greater calving ease issues, lower calf viability, lower milk production and lower fertility in cows, delayed puberty in heifers and longer finishing times.

 

“This is because the body has complex mechanisms to allow it share, or ‘partition’, resources between important functions; growth, health, lactation and fertility being some of the most important for farm profitability.

pic 1

Veterinary surgeon, Kaz Strycharczyk.

“Myostatin variants have faulty ‘brakes’ on appropriate muscle growth and so, assuming there are limits to energy (feed) provided, will prioritise muscle growth disproportionately.”

 

Fertility

 

It is up to the individual farm to decide whether the benefit of higher grades outweighs the potential reduced fertility, increased risk of calving issues (indirectly reducing fertility) and reduced milk yield.

 

To complicate the issue, different mutations are associated with different degrees of positive and negative traits.

 

“If you are a pedigree breeder, depending on your breed, you may already know the myostatin status of each animal. Different breed societies are at different stages – some have been testing for myostatin for years, while others have yet to start. if you are unsure, ask your breed society.

 

“On a commercial basis, your cows will be of unknown status. This means you cannot ‘match’ myostatin variants to avoid calves with double mutations. In this case you may opt to be more cautious with your choice of bull.

 

“If the status of your current stock bull(s) is unknown, genetic testing is available. Your vet will be able to advise you on the procedure and potential benefits of testing.

 

“Likewise, if you are looking to purchase a new bull but have a query about his myostatin status, they will be able to help with this too. Remember myostatin, despite wielding disproportionate influence for a single gene, is only one of many factors to consider when selecting a stock bull.”

How the parent’s genetics influence progeny

Number of myostatin mutation carried by each parent.

0

1

2

0

100% normal

75% normal, 25% single carrier

100% single carrier

1

75% normal, 25% single carrier

25% normal, 50% single carrier, 25% double carrier

50% single carrier, 50% double carrier

2

100% single carrier

50% single carrier, 50% double carrier

100% double carrier

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