Until this year, I hadn't given much thought to intramuscular fat. I've known it exists, I select a little bit for it in cattle, but there are so many other traits to select for in sheep that I basically ignored it.
As I'm sure you know, IMF stands for intramuscular fat. It's the marbling inside the loin muscle itself, not the fat sitting over the top of it. And it is one of the biggest drivers of how good lamb actually tastes. MSA's extensive consumer taste trials have demonstrated that IMF is one of the best indicators for how highly a consumer will rate the eating experience.
😋 Mmmmmm, delicious!
The Lambex Carcase Showcase
Last year we entered the Lambex Carcase Showcase. I had absolutely no idea how we'd perform. We'd already sent 80% of our lambs, so we only had the tail left!
But I'd been keen to send lambs to Gundagai for a couple years, having heard about the extra information they provide. Unfortunately, we're too far away, and they prefer to deal with clients closer than 900km...
So when I saw the Lambex Carcase Showcase advertised, I jumped on it, figuring they couldn't say no now!
I got the results back and was happy with 92% of our lambs grading GLQ+, more than paying for the freight with the premium. But I had no frame of reference to know if that was actually good or just alright.
Then I got a phone call from one of the showcase organisers, personally asking me to come and speak at the participant workshops because our lambs had performed well above the rest.
It was only in the results webinar that I could compare our results to the average of the Showcase. Our sheep were sitting up the top end of the bell curve for each category. Not just a slightly better average. Nearly every individual animal outperformed the average.
That sent me down the rabbit hole of working out exactly why...🐰
The below charts show the distribution of our sheep for IMF %, MSA index and LMY, compared to the Showcase averages.
How to increase IMF
From what we know so far (and I suspect there's still a lot we don't know), there are three main drivers of IMF: Finishing condition, Age/maturity, and Genetics.
🥩Finishing condition
Animals need to be in good condition with good fat coverage to have higher IMF. That's because IMF is generally one of the last deposits to be laid down after muscle and subcutaneous fat.
Skinny animals will basically never have high IMF. But just having a fat animal does not mean they will have IMF. There is more to the story.
🧓Age / Maturity
IMF develops as lambs approach maturity. A finished, young lamb will generally have less IMF than a similar condition, similar weight lamb that is 2 months older.
Being left with the tail of our lambs actually played in our favour in the LambEx Showcase because our lambs were 13-14 months old by the time they were able to kill them. Compared to 8 month old crossbred lambs, ours were more mature and had higher IMF.
As merino producers, this works well for us. We often want to hold onto our lambs to get a decent fleece off them, and then sell them at 10-12 months.
But again, just having older lambs won't guarantee IMF. There is still a huge variation between lambs that are the same weight, condition and age.
🧬Genetics
This is the real driver. Which is unsurprising if you think about Wagyu in cattle. It's the breeding that has driven the IMF gain.
There is now an ASBV in sheep for IMF. It's a difficult to measure trait, since you currently can't measure it until the animal is dead. So I wouldn't be pegging my livelihood against its accuracy.
The good news for us is that fat depth (YFAT) is positively linked to IMF. On top of that, finer wool flocks tend to already sit ahead on eating quality traits. Chasing fine wool and doability the way we always have has happily resulted in our having higher IMF!
The sort of lambs that went to the LambEx Carcase Showcase
Is it actually worth looking at IMF right now?
Yes. And No. Like much of life, the real answer is, it depends.
The tools are there, so it is now possible to make gains. If you are selling your lambs to Gundagai and getting rewarded for IMF, then it makes a bit of sense to put some selection pressure on IMF.
MLA are also developing a quality scheme for lamb, same as the MSA grading in cattle. In fact, one of the drivers for the LambEx Showcase was just for MLA to get more data on eating quality traits. At some point in the future, there will be more widespread premiums for better eating quality.
But we don't know when. It could be 2 years, or it could be over 10.
If you run wethers, or if you don't have a lot of surplus lambs to sell, then IMF is definitely not your focus. Better quality wool or better reproduction would be more valuable to you.
Look at your genetic plan and chase the lower hanging fruit first.
For ourselves, we have put a bit of weighting on it. It will be a valuable trait to have in the future, and we'd rather be ahead of it than catching up in five years.
We didn't put IMF in our main catalogue for 2026, but if it's something that interests you, you will find IMF ASBVs in our excel catalogue or on Sheep Genetics. Half the catalogue is in the top 30% of the breed, including some in the top 1%.
It won't be the trait that makes or breaks your operation this year, but it might be something for you to consider.