Myostatin testing: Is more info needed when choosing bulls?

As the quest to refine and improve farmers’ decisions on optimal breeding for Limousin cattle continues, the topic of myostatin testing is coming more to the fore.

In recent years, the British Limousin Cattle Society has introduced such testing for many of its pedigree bull sales, offering individual myostatin test results for animals on offer at its standout shows, from 2015 onwards.

Such technology has also taken off on this side of the Irish Sea, with some AI entities now offering bulls with results for breeders’ consideration.

What is myostatin?

The myostatin gene influences the production of a protein that controls the development of muscle in mammals.

Natural mutations have produced proteins that are less effective in controlling this, resulting in increased muscle mass – or the ‘double muscling’ effect.

There are nine mutations of the myostatin gene in cattle; some of these only affect one breed of animal, while others impact on multiple breeds.

There are three main mutations which are most common in Limousin cattle among other breeds: F94L; NT821; and Q204X.

Benefits of these include improved meat yield and meat quality from all three genes. Disadvantages of both NT821 and Q204X, however, include greater calving difficulty and bigger calves at birth.

Animals that carry two copies of such variant genes are known as homozygous, while cattle with one copy are known as heterozygous.

Both homozygous and heterozygous cattle will have increased muscle mass, more so in the former due to multiple copies; although these also have greater calving difficulty.


To learn more on the topic, AgriLand caught up with pedigree breeder Kelly Stephenson, who recently had all of her Limousin herd myostatin tested.

Kelly – who also works for Progressive Genetics, as covered by AgriLand previously – explained that when reading up on it, she noted the moves being made in the UK.

Kelly said that she had seen the moves the British Limousin Society was making – with myostatin testing now compulsory for most of its bigger sales – and researched the matter herself, deciding to test her herd and see where she stood.

She stressed that she doesn’t know for sure if anything will come from the testing, or if it will be disproven in time – but she remains optimistic.

Kelly said that previously she had a couple of good-sized heifers that had to be cesarean sectioned and ended up losing the calves – despite using ‘easy-calving’, well-proven bulls of 70-80% reliability.

“We were expecting them to be easy-calving – and then we had these monsters of calves,” the pedigree breeder said, adding that the dry period management was good, with the animals neither underfed nor overfed, leading to some confusion at the time.

One day, in conversation with colleagues, the topic of myostatin in bulls came up.

“I was saying ‘I wonder do my cows have it? Is that why it happened?’ We’ve other cows and they had calves no problem by this certain bull, and lads were saying ‘oh he’s a monster for calving’.

“We had four of them fine; three calved on their own, one we pulled – nothing crazy.

When I looked it up, the heifers that lost their calves all carried one gene, and carried an F as well – so they carried a Q and an F – and then the bull I used carried an N and an F.

The cows which had no difficulties calving with hard-calving bulls had no ‘hard-calving’ genes, with just two Fs.

“It’s just something I wanted to find out, because we were hearing about all these ‘easy’ calvings and they weren’t easy for us – and then all the ‘hard’ calvings which were fine for us,” Kelly said.

“We’ll see in time to come is that the link or is it something else.

In a few years I do think the farmers will be looking for certain genes. Now, I don’t know which ones they’re going to be, so it’d be nice to be kind of hitting the ground running.

If it does have such an effect on increased meat yield, and more weight in the cattle, Kelly is of the view that farmers will be looking for it.

“Just to be ahead of it if possible – it might come to nothing when they find out more about it but I just thought it was interesting and it would be good when you’re making your breeding decisions.

“If you know you had a bull carrying and your heifer is carrying as well, you probably wouldn’t use the bull – for your first calving anyway.”


Regarding pricing, and the cost of getting the testing done, Kelly explained that, if an animal is genotyped, it costs €5/head. If not already done, genotyping costs about €22 with ICBF.

Kelly noted that if it cost a couple of hundred euro to get the herd done, should myostatin testing mean that calving difficulties were decreased and only one calf was saved through different breeding, it would be worth it.

Regarding research beforehand, the pedigree Limousin breeder said that it’s still early days for the testing, and there’s not a lot out there on the subject apart from a few scientific journals.

It’s no harm in knowing these things. Whether it makes a difference in the long term or not, if they prove it all wrong; well, it was no harm knowing. The more information you have on your animals, the better.

“The big thing for me is to just use it in our breeding programmes, and it’s just to be ahead of the market if farmers do want double-muscled bulls or if they don’t want double-muscled bulls in the future.”


With testing quite breed-specific, it was asked whether – if successful – the testing could be commonplace for other breeds.

Kelly said that, while myostatin variant genes are in a lot of breeds, they are a lot more commonplace in Limousin cattle as a population.

I think Limousins are nearly all carrying the F anyway if they’re not double-muscled – if they don’t have the double myostats, they’re all carrying an F anyhow.

As a result, for the minute, the focus remains on testing Limousins only for Kelly, who also breeds Aubracs.

While Kelly believes that suckler farmers will find it hard to justify paying for it at present, unless a real value is proven to doing it, she expects a good uptake among pedigree herds.

If testing means even one calf is saved from picking the right bull, the testing would be worth it, she contended.

However, nothing is ruled out just yet.

“I don’t know an awful lot on it – that’s why I did it; just to see can I learn as I go along,” Kelly said.