Looking to breed more muscled cattle without compromising on calving ease? Then assessing the myostatin status of both the cows in your herd and the sires used will be a key task ahead of next season’s breeding season.

Discussing all things myostatin at the Teagasc National Beef Conference in Athenry, Co. Galway, on November 18, Dr. Katie Quigley, a geneticist with the Irish Cattle Breeding Federation (ICBF), outlined the breeds in which the myostatin mutation – a change within an individual animal’s genetic makeup that allows for the development of more muscle mass and the potential for increased calving difficulties, on occasion – is most frequent.

“Within the Irish suckler herd, the most frequent myostatin gene variations we observe are F94L, Q204X and nt821. These myostatin variants are present in many beef cattle breeds, such as Aubrac, Belgian Blue, Charolais and Limousin, among others.

“All animals will have two copies of the myostatin gene, one inherited from the cow and the other from the sire.

“And depending on whether the animal inherits a normal copy or a mutated copy of myostatin, the animal will be termed homozygous non-carrier (two copies of the normal myostatin gene), heterozygous (one normal and one mutated copy of the myostatin gene) or homozygous carrier (two copies of the mutated gene inherited).” Dr. Quigley explained.

As to the impact of these myostatin mutations on animal performance, Dr. Quigley looked to research, some key findings discussed on the night included:

• Some variants of the myostatin gene are more disruptive than others. nt821 (most frequent in Belgian Blue) and Q204X (commonly occurring in Charolais and Limousin cattle) are more disruptive than the F94L (mostly associated with Aubrac and Limousin cattle).
• Myostatin variants F94L, Q204X, and nt821 were associated with heavier, more conformed and leaner carcasses than their non-carrier counterparts.
• Although nt821 and Q204X were associated with improved carcass merit, they were also associated with more difficult calvings when present in the dam or the calf, most likely due to a narrower pelvic opening in the dams combined with those dams giving birth to larger calves.

Weanling returns

With the mutations being associated with increased muscle mass, Dr. Quigley also turned to mart data from 2020 to 2025 to illustrate how weanlings carrying none, one or two copies of F94L, nt821 and Q204X performed in the sales ring.

“On average, weanlings carrying one or two copies of a myostatin variant were sold for slightly higher prices when compared to those not carrying any myostatin variant; however, this was dependent on which myostatin variant the animal carried,” Dr. Quigley explained.

Some key findings from this analysis include:

• The smallest price difference was observed in those carrying the F94L variant. On average, those carrying one copy of F94L made €20 more than those not carrying any copy of a myostatin variant.
• Those carrying two copies of the F94L variant made, on average, €85 more than those not carrying any copy of a myostatin variant.
• In cattle carrying one copy of the nt821 variant, an average of €92 more was made when compared to those not carrying any copy of a myostatin variant.
• Cattle carrying two copies of the nt821 variant made, on average, €325 more than those not carrying any copy of a myostatin variant.
• Those carrying one copy of the Q204X variant made, on average, €113 more than those not carrying any copy of a myostatin variant.
• Those carrying two copies of the Q204X variant made, on average, €246 more than those not carrying any copy of a myostatin variant.

“While these insights are useful, it is important to remember that market value is influenced by many other factors, including breed, management and overall genetic merit,” Dr. Quigley added.

Dr Quigley spoke to Teagasc Beef Specialist, Catherine Egan at the Teagasc National Beef Conference. Watch the video below:

Calving difficulty

For farmers selecting sires in advance of the breeding season, Dr. Quigley also shared details of a useful analysis that examined the variability in calving difficulty and carcass traits of sires based on their myostatin status.

Examining AI sires that have a ≥90% reliability on the beef cow calving difficulty sub-index, Dr. Quigley noted that sires carrying two copies of the nt821 myostatin variant had a median calving difficulty of 10%, ranging from 5.2% to 15.8%, while the calving difficulty for AI sires carrying one copy of the Q204X myostatin variant ranged from 4.8% to 11.5%, with a median of 6.2%. Those AI sires not carrying any copy of a myostatin variant had a median calving difficulty of 3.2%, ranging from 1.7% to 5.8%. This shows that bulls carrying no copy of a myostatin variant may still have higher calving difficulty than those bulls carrying one or two copies of a myostatin variant, and why it is important to interpret myostatin status alongside breeding indexes.

Table 1:  Median, maximum and minimum beef cow calving difficulty and carcass weight PTAs for AI sires carrying myostatin variants and having ≥90% reliability on the beef cow calving difficulty sub-index.

Concluding her presentation, Dr. Quigley said: “Myostatin status is additional information that may be used when making breeding decisions to improve the carcass weight and conformation of the progeny produced, but it should be interpreted alongside breeding indexes.

“Where high quality samples have been received, genomics now means that the myostatin status of an animal can be assessed by ICBF members through their genomic profiles on ICBF.com or via the ICBF HerdPlus app and are also available to breed societies on pedigree certificates and sales catalogues.”

For full insights, Dr. Quigley’s full paper to the Teagasc National Beef Conference is available to read here (PDF).

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