MIA Focus: Chewing the intramuscular fat

Cameron Craigie, AgResearch
On the IMF case is Dr Cameron Craigie, AgResearch science impact leader for meat products and supply. He is leading the New Zealand team of meat researchers looking into intramuscular lamb fat.

Very fatty lamb, common pre-1980s, is officially a thing of the past. Responding to consumer and customer demands, the red meat industry successfully and efficiently selected and managed the right kind of sheep for lean lamb. But, has the drive to reduce fat levels under the skin been too efficient, at the expense of intramuscular fat, affecting New Zealand lamb’s taste and tenderness?

Now a team of New Zealand meat researchers is looking right into the meat muscles, to determine what the optimum level of intramuscular fat (IMF) should be for high eating quality, how to objectively measure the levels and whether the genetic traits for IMF levels are heritable. They are led by Dr Cameron Craigie, geneticist and AgResearch science impact leader for meat products and supply, working with Beef + Lamb Genetics and food companies Alliance Group and Progressive Meats.

Craigie points to a European case-study on pork.

“In the 1980s, concern about fat levels led to leaner pigs being produced. While this met consumer demand, it meant the quality of the pork diminished as it was drier and blander,” Craigie says adding efforts are now being made in Europe to redress the balance.

The same thing is happening here with lamb, he says.

“As New Zealand has produced the same amount of lamb from fewer sheep, fat levels have dropped. Schedule payments to farmers are paid on growth – per kg of lamb produced – which has been at the expense of lamb quality,” he says.

Australian studies have shown selection for leanness results in reduced levels of IMF in lamb throughout the carcase, explains Craigie.

But where to draw the line?

Work in the IMF lamb study, supported by Beef + Lamb NZ Genetics, Progressive Meats, Alliance Group and AgResearch strategic science investment support, started four years ago and has a very strong genetic component, he explains.

Three percent IMF optimum in lamb?

Craigie’s first task was to get a handle on it through understanding the genetics behind the complex interactions between fat levels and growth. He now has at his disposal the results from thousands of lambs over multiple years in Beef + Lamb NZ Genetics’ lamb Central Progeny Tests (CPT) – which are following certain genetic traits through a flock’s offspring.

“Our work in the loin cut suggests there is an optimum IMF percentage of between 2.5 to three percent for New Zealand lamb,” he says, adding, however, that about half of New Zealand’s lamb loin cuts do not currently reach that target. “And, we do not really know if the loin IMF is a good indicator of the IMF in other cuts within a lamb carcase.”

The AgResearch team is now seeking funding to establish the optimum carcase fat thresholds for lamb production and consumption.

Dr Tricia Johnson, AgResearch Invermay.
Dr Tricia Johnson, an AgResearch senior scientist, reported to the AgResearch Meat Industry Workshop in March.

Successful objective measurement

Participants at last month’s AgResearch Meat Industry Workshop were updated on the latest results of the team’s work by AgResearch senior scientist Dr Tricia Johnson, from AgResearch’s Animal Genomics team at Invermay.

IMF is a key driver of meat palatability and is directly linked to flavour, tenderness and juiciness, she told the audience.

“Any variation in the percentage of IMF is linked to consumer acceptability of red meat products,” she said.

The team has been trialling the use of near-infrared spectroscopy (NIR) and hyper-spectral imaging (HSI) to objectively measure IMF%, without destroying the meat, as traditional methods of wet chemistry analysis and visual assessment can do, and has found it can accurately and quickly achieve high levels of prediction.

Further, using prediction equations developed earlier, but with ongoing calibration, they have used the data to predict variations in IMF successfully in real-time selection of lamb loin cuts for the first time, she reported.

IMF% highly heritable trait

In addition, genetic traits for IMF% have also been shown to be highly heritable.

Investigate genetic variation
A slide from Dr Johnson’s presentation showing the heritability of certain genetic traits in the B+LNZ Genetics progeny test lambs.

B+LNZ Genetics Central Progeny Test lambs processed through Alliance Group’s Smithfield, Dannevirke and Lorneville meat plants in 2014 and 2015 were chemically analysed for IMF%. Of the 1,434 carcases that were analysed, the trait for IMF% was shown to have an 0.83 heritability factor (measured on a scale from 0 to one), close to the predicted 0.77. This was further supported by Scottish work in the area, which had suggested 0.88.

“The work showed a very high genetic correlation between carcase (subcutaneous) fatness and measured IMF percent and also a high negative genetic correlation between carcase lean yield and actual IMF,” said Johnson. “As international literature, and logic, suggest, there is an antagonistic relationship between lean yield and IMF.”

Delivering the good news for the New Zealand red meat industry, she said: “The correlation, while not perfect, is that we can achieve IMF level and carcase lean in both, if both are measured.

“There are some animals that can achieve that, so information needs to go to lamb breeders so they can use it in their programmes to optimise for lean meat yield and IMF%.”

In-plant capability would be ideal, said Johnson.

Craigie is working to that end, leading another Ministry of Business, Innovation and Employment (MBIE)-funded project, now in its second year, investigating a new sensory device capable of earlier in-plant detection of IMF and other meat quality parameters, including pH and tenderness.

IMF key to Alliance Group’s lamb eating quality programme

Gary Maclennan, Alliance
Gary Maclennan, Alliance

The commitment of Alliance Group to the IMF research has been integral to the progress made to date. The cooperative’s marketing development services manager Gary Maclennan, who works closely with the AgResearch meat scientists in the design of and implementation of the studies, says Alliance first identified IMF as an important element in lamb eating quality some years ago.

“We started looking at a whole range of meat quality attributes a decade ago and identified IMF was heavily linked to eating quality.”

While the current AgResearch work has been partially linked to The Omega Lamb Project, a Primary Growth Partnership programme involving Alliance Group, the Ministry for Primary Industries and Headwaters, the co-operative is looking at the area from a wider perspective, says Maclennan.

“It’s a key part of Alliance Group’s meat research programme to lift lamb eating quality and, with that, the value of our products and returns to our farmer shareholders.”

He says the cooperative is “very keen” to get the message across to consumers that its grass-fed red meat is a high quality, nutritionally rich and healthy product, especially as a source of Omega-3 fatty acids.

While Alliance has no official target set for IMF%, it is working towards a three percent provisional target. “Work to date has identified effects that have a genetic basis as well as effects associated with animal feed type and animal age (seasonality),” says Maclennan.

“But, we do know there are some superstar animals out there,” says Maclennan. “One CPT ram we’ve identified leaves offspring with an average IMF% several orders of magnitude above others,” says Maclennan.

Word about the IMF trait is starting to get out amongst breeders. Elite Charollais, a Central North Island stud recently approached AgResearch and paid for a genetic study for muscularity and IMF on its Charollais sheep processed through Alliance Dannevirke.

“We are keen to support any B+LNZ Genetics linked Central Progeny Test initiatives,” says Maclennan.

“We see improvements in animal genetics linked to productivity and eating quality traits as critical to the future of the New Zealand sheepmeat industry.”

This is a longer version of an article which appeared in Food NZ magazine (June/July 2018) and is reproduced here with permission.

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