Monday, April 15, 2024
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Why Grass Finished Beef Marbling Is Difficult

Thanks to Seth Christensen of Christensen Genetics for helping make this article possible.

Brad Johnson, an expert on skeletal and muscle growth in cattle, and his colleague Stephen Smith, may have found one of the reasons that it’s more difficult to get marbling in grass finished beef. It’s a result of the kind of energy required to create intramuscular fat, and the difficulty of providing that with a forage only diet.

As cattle develop, they actually create two different kinds of fat – subcutaneous (under the skin) fat and intramuscular fat, or marbling. Consumers prefer lean, marbled beef because it is very high in a healthy fatty acid called oleic acid. Oleic acid is a monounsaturated fatty acid that, in humans, has been shown to decrease low-density lipoprotein (LDL) cholesterol (what we know as “bad” cholesterol) and possibly increase high-density lipoprotein (HDL) cholesterol or “good” cholesterol. It also has been linked to lowering blood pressure.

According to Johnson, “Generally, if you can avoid backfat and consume lean tissues that have marbling, it contains a lot of oleic acid, which is beneficial for human health. That story has to be told many times to consumers because many see any fat as being negative to their diet.”

Here you can see marbling in US and Japanese grading systems (BMS) courtesy of Japanese Wagyu cattle producer about 30-35% intramuscular fat. That compares to high-end steakhouses here in the U.S. serving prime steaks with about 6-8% marbling. Johnson notes that achieving Wagyu marbling would require much longer feed times, and because consumers are not willing to pay the additional premium, it doesn’t make economic sense for North American producers.


Johnson, a professor at Texas Tech’s College of Agricultural Sciences and Natural Resources professor, and the Gordon W. Davis Regent’s Chair in the Department of Animal and Food Sciences, partnered with Texas A&M professor Stephen B. Smith to discover the key to increase marbling without increasing external fat. What they learned is that backfat and marbling are made of two different kinds of fat cells or adipocytes.

Johnson and Smith isolated the two types of adipocytes and grew them in culture systems to get a better find out more about how they function. They learned that marbling adipocytes are much smaller in size and diameter than subcutaneous adipocytes, which tend to clump together. Another difference is metabolic, or which energy source they use to produce backfat or marbling. Backfat adipocytes use acetate, which is a volatile fatty acid produced in the rumen of cattle. Marbling adipocytes, however, require glucose, which Johnson said is a premium energy source for both animals and humans. Animals fed grain have access to the glucose they need to develop marbling adipocytes.

“What happens in the rumen when animals consume grass or roughage, their fermentation pattern is such that it reduces marbling even more,” Johnson said. “They have fewer amounts of oleic acid for beef. Grain feeding very much promotes marbling deposition. That’s one thing we do in feedlots that does promote marbling.

So, what can grass finished producers do?

In next week’s issue, we’ll share another excerpt from the Producer’s Guide to Pasture-Based Finishing that describes how some producers finish on pasture and add a bit of grain to improve marbling and the product they provide their customers.

Another option is to feed cattle longer. Johnson says the longer cattle feed, the more they are able to replace saturated fats with unsaturated fats, such as marbling. How does that happen? As Johnson explains, cattle release an enzyme called stearoyl-CoA desaturase, which takes steric acid, a saturated acid, and saturates it to form double bonds to convert it into oleic acid.

“As the animal matures, it gets fatter, has more days on feed, it increases the activity or this enzyme,” Johnson said. “So, in fact, we are creating more monounsaturated fat.”

Improved genetics is another option. I spoke with Seth Christensen of Christensen Genetics to get his take on how genetics might factor into this. Here’s what he shared:

“First, let me be absolutely clear on one thing: marbling is not the be all and end all of cattle breeding. It is another tool in the toolbox to create an animal that will satisfy its purpose. I do highly recommend focusing on marbling when looking to produce an animal that will be sold as finished beef. Here’s one way that this could be accomplished.

This Christensen’s AI sire is an example of a bull with high marbling.

“Let’s say that you’ve developed a highly maternal, efficient, low maintenance herd of beef cows. This is excellent! You’re able to keep your costs down, make feed go further, and maintain great breed up rates. Now, you’re looking at potentially expanding into the grassfed beef market in order to capture more value from your calves. Your cows will already provide the ability to grow and gain on grass alone. Consider selecting a high marbling, terminal sire to improve the quality grade of the resulting offspring from your cows. While this isn’t the sire you’d want to keep replacement heifers from, he could do an excellent job of helping you to produce grassfed beef. The use of sexed semen makes this option even more appealing: you can use male sexed semen on terminal sires to make the best grassfed beef, and female sexed semen on maternal sires to make the next generation of ideal mother cows.

Wagyu is a breed of Japanese cattle that includes different varieties. In this photo you see 1) Japanese black, 2) Japanese shorthorn, 3) Japanese polled and 4) Japanese brown, also known as Akaushi.

“Just like not all kids are built to play basketball, not all cattle are built to end up as a well-marbled cut of beef. Choosing the right genetics can help produce a finished product with more intramuscular fat.  Consider this: the national average for percent of carcasses to grade prime (the highest USDA quality grade) has been estimated over the last five years to range from 4 – 8%.  At a prominent ranch in Idaho, a semi load of sires from a particularly high marbling Angus sire went 43% prime. In another example, F1 Akaushi calves from a LimFlex herd in southern Idaho went 80% prime. These results are literally ten times better than industry average. Whether you choose Angus, Akaushi, or another breed, it is important to realize the massive differences in marbling potential based on genetics.”

In the meantime, Johnson and Smith are continuing their own research into increasing marbling in our meat. “My whole goal was to be able to get high-marbled beef without having to spend a lot of money on feed,” Johnson said. “That’s still my goal from a sustainable beef producing standpoint. If we can get a high quality, healthy product on fewer days on feed, I think that will be very favorable.”

May all your steaks be well-marbled!

P.S. With all this talk of genetics and marbling, remember that you also need to choose animals that fit your environment and meet your economic goals.

Here’s the next in the series:

Production Systems for Pasture-Finished Beef – Part 1

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