Myostatin

Myostatin

Myostatin is a gene that is connected to the production of proteins that affect muscle development.  When the gene is “switched off” or “deleted”, muscle mass can continue to increase more than it should.  So myostatin status will influence your cattle breeding programme.

The myostatin variant found most frequently in the South Devon breed is ‘nt821’ which is known as ‘disruptive’.  A lesser number of animals in the breed carry the ‘F94L’ myostatin variant which may be associated with lower birth weight.

Knowing the myostatin status of your animals will help in the selection of bulls and female breeding replacements so that the mating match will be as productive and safe as possible.  However, it is just one tool which should be used in conjunction with the wider information available such as EBVs, pedigree, and most importantly your own judgement and eye.

All South Devon pedigree registered bulls are DNA tested to determine their myostatin status, such information being published in the catalogue and on pedigree certificates.  Although it is not obligatory to test females for myostatin status, some breeders choose to do so and the result is published where known. The status is expressed as either:

0  – No copy of the deleted myostatin gene,

1  – Heterozygous, so carrying one copy of the deleted myostatin gene (inherited from one or other parent)

or

2  – Homozygous, so carrying two copies of the deleted myostatin gene (inherited from both parents)

The table below shows the chances of inheriting depending on the myostatin status of the parents.

Both parents homozygous

(2 x ‘2’ status)

100% chance of homozygous

progeny (‘2’ status)

One parent homozygous (‘2’ status)

One parent heterozygous (‘1’ status)

50% chance of homozygous

progeny (‘2’ status)

50% chance of heterozygous

progeny (‘1’ status)

One homozygous parent (‘2’ status)

One non-carrier parent (‘0’ status)

100% chance of heterozygous

progeny (‘1’ status)

Both parents heterozygous

(2 x ‘1’ status)

25% chance of homozygous

progeny (‘2’ status)

50% chance of heterozygous

progeny (‘1’ status)

25% chance of non-carrying

progeny (‘0’ status)

One parent heterozygous

(1 x ‘1’ status)

One parent non-carrier

(1 x ‘0’ status)

50% chance of heterozygous

progeny (‘1’ status)

50% chance of non-carrying

progeny (‘0’ status)

Both parents non-carriers

(2 x ‘0’ status)

100% chance of non-carrying

progeny (‘0’ status)

 

The implications for an animal having one or two copies of the ‘nt821’ deletion have been researched by the Roslin Institute.  Their findings were that this particular deletion tends to improve muscle conformation, reduce fat, and increase hot weight at slaughter.  But it also tends to increase birthweight, decrease calving ease, reduce weight gain, reduce internal organ and bone size, and reduce eating quality.  These effects are most obvious when the animal has two copies (‘2’) of the ‘nt821’ variant, one inherited from each parent.

No formal research has been carried out within the breed on the ‘F94L’ deletion to date in this country, but calving data shows smaller birth weights followed by good growth.