10 Agricultural Research/July 2004

ore than a century ago, Euro-pean ranchers produced beefy,well-muscled cattle throughselective breeding—without

understanding how or why their genetictinkering worked. In the 1990s, severalAgricultural Research Service (ARS)scientists, after years of searching for thereason, helped pinpoint a major gene incattle responsible for boosting musclesize and leanness.

Since then, ARS researchers haveadded to their understanding of this gene,which codes for the protein myostatin,with the ultimate goal of providing con-sumers with cuts of beef that are not onlylean, but also tender. They work to pro-vide ranchers with information and tech-nology needed to produce such beefprofitably and sustainably.

Myostatin limits muscle growth incattle—and in humans. If the gene re-sponsible for producing myostatin is al-tered so that it makes an inactive formof the protein, or the gene is intentional-ly suppressed, the result is more muscleand less fat. ARS researchers are work-ing to find optimal ways to use thisgene—alongside others—to make beefmore healthful, without sacrificing tasteand tenderness.

Love Meat TenderA benefit of inactivated myostatin—

and one likely to be popular withconsumers—is beef that’s more tender.“Previous researchers tested just the ribeye cut. But we found that with thealtered myostatin gene, all cuts of beefhave improved tenderness,” says TommyL. Wheeler, a food technologist at ARS’sRoman L. Hruska U.S. Meat AnimalResearch Center (MARC) in Clay Cen-ter, Nebraska. Now low-quality cuts ofbeef, which are usually tough, can bepalatable and tender.

And it’s not just consumers who bene-fit. “Even if their cattle have just onecopy of the modified gene, ranchers canexperience a 7-percent yield increase insalable carcass,” says Wheeler.

Production of leaner beef is also moreenergetically efficient. “But most cattleproduced in the United States still con-tain nearly twice the amount of carcassfat considered optimal,” says Michael D.MacNeil, an animal geneticist at ARS’s

This Piedmontese-Hereford crossbredcalf displays classicdouble musclingbecause it inherited adefective myostatingene from both of itsparents.

KEITH WELLER (K8448-2)

Can YouHaveYour

BeefEat ItToo?and

ARS researchbrings healthful—and tender—beefto your table.

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11Agricultural Research/July 2004

Fort Keogh Livestock and RangeResearch Laboratory in Miles City,Montana. This is because the currentgrading system pays top dollar for beefthat contains more marbling—and mightbe more tender—despite consumer pre-ference for lean beef. Thus, productionof lean and tender beef could be a bigadvantage for ranchers.

Handle With CareMyostatin manipulation seems like a

promising genetic tool, but it requires alevel of caution. A condition known asdouble muscling occurs in animals thatinherit a defective myostatin gene fromboth parents. “Double-muscled calvesare extremely muscular at birth, leadingto difficulty in exiting the birth canal,”says MARC animal geneticist TimothyP.L. Smith. Even after a successful birth,calves that can’t produce activemyostatin are less likely to survive.

Inheriting two copies of the geneproducing inactive myostatin can alsoreduce fertility and decrease the pel-vic area of females, which may fur-ther contribute to birthing problems.Double-muscled animals can alsohave a lower tolerance for stress. Be-cause of these problems, some coun-tries now ban use of cattle with dou-ble muscling.

ARS research hopes to continue toshed light on the gene, particularly inthe context of beef production. “Weprobably know the major effects ofmyostatin, but some of its minor onesare still unknown,” says MacNeil.One desirable approach is to cross bullshaving genes that make only inactive my-ostatin with cows having genes that makeonly the active form.

The gene that codes for the inactiveform of myostatin is found more oftenin breeds like Piedmontese and BelgianBlue. Researchers can cross these lean,well-muscled breeds with ones tradition-ally used for beef production, such asAngus and Hereford. The resulting ani-mal yields beef cuts lower in saturatedfat, satisfying many health-consciousconsumers. These crossbred cattle alsogrow faster than animals that are 100percent Piedmontese or Belgian Blue,assuring breeders and ranchers maxi-mum returns.

Other Ways To Get LeanFor all the benefits—and problems—

associated with the myostatin gene, ge-netic factors contribute to only about halfof what determines tenderness and lean-ness. Environmental and physical fac-tors, such as feed type, length of time onfeed, animal stress, carcass processingtechnology, and cooking methods, alsofactor in.

To produce more-healthful beef, re-searchers and breeders can also look toLimousin and Charolais cattle, whichnaturally have a strong genetic potentialtowards lean tissue. It appears that theseanimals achieve their leanness as a re-

Differences are apparent in lean-to-fat ratios withinthese cuts of meat from cattle having no (top), one(center), or two copies (bottom) of the inactivemyostatin gene.

sult of several genes, each exerting asmall effect. ARS research is evaluatingstrategies to use these breeds, as well asthose that produce inactive myostatin, tobest meet production needs and consum-er demands.

To further flesh out understanding ofthe genes that relate to fat deposition,MacNeil is studying animals not usuallyfound on U.S. ranches—Wagyu cattle.This Japanese breed is associated withthe highly marbled luxury known asKobe beef, which contains up to 45 per-cent fat. The experimental cattle madetheir way to Miles City in 1999 after aresearch farm at Washington State Uni-versity was closed.

In crossing Wagyu cattle with Lim-ousin cattle, MacNeil, colleague LeeAlexander, and university partnerscreated a genetic resource they can tap

for more clues about the genes thatplay a role in deposition of fat andfatty acid composition.

Wheeler and his MARC col-leagues, including Steven Shackel-ford and Mohammad Koohmaraie,compared Wagyu to other breeds andfound that they possess carcass andmeat-quality traits very similar to An-gus when produced in typical U.S.production systems. Wagyu cattle notdestined to become Kobe beef yieldleaner carcasses than Angus and oth-er British breeds, but they also growmore slowly and less efficiently thanother breeds.—By David Elstein andErin Peabody, ARS.This research is part of Food Animal

Production, an ARS National Program(#101) described on the World Wide Webat www.nps.ars.usda.gov.

Michael D. MacNeil is with theUSDA-ARS Fort Keogh Livestock andRange Research Laboratory, 243 FortKeogh Rd., Miles City, MT 59301; phone(406) 232-8213, fax (406) 232-8209,e-mail mike@larrl.ars.usda.gov.

Timothy P.L. Smith and Tommy L.Wheeler are with the USDA-ARS RomanL. Hruska U.S. Meat Animal ResearchCenter, Spur 18D, Clay Center, NE68933; [Smith] phone (402) 762-4366,fax (402) 762-4390, e-mail smith@email.marc.usda.gov; [Wheeler] phone (402)762-4229, fax (402) 762-4149, e-mailwheeler@email.marc.usda.gov. ★

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