crossbred calf displays
classic double muscling
because it inherited a
defective myostatin gene
from both of its parents.
More than a century ago, European ranchers produced beefy, well-muscled
cattle through selective breedingwithout understanding how or
why their genetic tinkering worked. In the 1990s, several Agricultural
Research Service (ARS) scientists, after years of searching for
the reason, helped pinpoint a major gene in cattle responsible for boosting
muscle size and leanness.
Since then, ARS researchers have added to their understanding of this
gene, which codes for the protein myostatin, with the ultimate goal
of providing consumers with cuts of beef that are not only lean, but
also tender. They work to provide ranchers with information and technology
needed to produce such beef profitably and sustainably.
Myostatin limits muscle growth in cattleand in humans. If the
gene responsible for producing myostatin is altered so that it makes
an inactive form of the protein, or the gene is intentionally suppressed,
the result is more muscle and less fat. ARS researchers are working
to find optimal ways to use this genealongside othersto
make beef more healthful, without sacrificing taste and tenderness.
Meat from cattle having
no copies of the inactive
myostatin gene. This meat
has a lower lean-to-fat ratio
(it's fattier) and more marbling
than meat from cattle
having one or two copies
of the gene.
Love Meat Tender
A benefit of inactivated myostatinand one likely to be popular
with consumersis beef that's more tender. "Previous researchers
tested just the rib eye cut. But we found that with the altered myostatin
gene, all cuts of beef have improved tenderness," says Tommy L.
Wheeler, a food technologist at ARS's Roman L. Hruska U.S. Meat Animal
Research Center (MARC) in Clay Center, Nebraska. Now low-quality cuts
of beef, which are usually tough, can be palatable and tender.
And it's not just consumers who benefit. "Even if their cattle
have just one copy of the modified gene, ranchers can experience a 7-percent
yield increase in salable carcass," says Wheeler.
Production of leaner beef is also more energetically efficient. "But
most cattle produced in the United States still contain nearly twice
the amount of carcass fat considered optimal," says Michael D.
MacNeil, an animal geneticist at ARS's Fort Keogh Livestock and Range
Research Laboratory in Miles City, Montana. This is because the current
grading system pays top dollar for beef that contains more marblingand
might be more tenderdespite consumer preference for lean beef.
Thus, production of lean and tender beef could be a big advantage for
Meat from cattle having
one copy of the inactive
myostatin gene. This meat
has a medium lean-to-fat
ratio and medium degree of
marbling compared to meat
from cattle having no
or two copies of the gene.
Handle With Care
Myostatin manipulation seems like a promising genetic tool, but it
requires a level of caution. A condition known as double muscling occurs
in animals that inherit a defective myostatin gene from both parents.
"Double-muscled calves are extremely muscular at birth, leading
to difficulty in exiting the birth canal," says MARC animal geneticist
Timothy P.L. Smith. Even after a successful birth, calves that can't
produce active myostatin are less likely to survive.
Inheriting two copies of the gene producing inactive myostatin can
also reduce fertility and decrease the pelvic area of females, which
may further contribute to birthing problems. Double-muscled animals
can also have a lower tolerance for stress. Because of these problems,
some countries now ban use of cattle with double muscling.
Meat from cattle having two
copies of the inactive myostatin
gene. This meat has a higher
lean-to-fat ratio (it's leaner)
and less marbling than meat
from cattle having no or one
copy of the gene.
ARS research hopes to continue to shed light on the gene, particularly
in the context of beef production. "We probably know the major
effects of myostatin, but some of its minor ones are still unknown,"
says MacNeil. One desirable approach is to cross bulls having genes
that make only inactive myostatin with cows having genes that make only
the active form.
The gene that codes for the inactive form of myostatin is found more
often in breeds like Piedmontese and Belgian Blue. Researchers can cross
these lean, well-muscled breeds with ones traditionally used for beef
production, such as Angus and Hereford. The resulting animal yields
beef cuts lower in saturated fat, satisfying many health-conscious consumers.
These crossbred cattle also grow faster than animals that are 100 percent
Piedmontese or Belgian Blue, assuring breeders and ranchers maximum
Other Ways To Get Lean
For all the benefitsand problemsassociated with the myostatin
gene, genetic factors contribute to only about half of what determines
tenderness and leanness. Environmental and physical factors, such as
feed type, length of time on feed, animal stress, carcass processing
technology, and cooking methods, also factor in.
To produce more-healthful beef, researchers and breeders can also look
to Limousin and Charolais cattle, which naturally have a strong genetic
potential towards lean tissue. It appears that these animals achieve
their leanness as a result of several genes, each exerting a small effect.
ARS research is evaluating strategies to use these breeds, as well as
those that produce inactive myostatin, to best meet production needs
and consumer demands.
To further flesh out understanding of the genes that relate to fat
deposition, MacNeil is studying animals not usually found on U.S. ranchesWagyu
cattle. This Japanese breed is associated with the highly marbled luxury
known as Kobe beef, which contains up to 45 percent fat. The experimental
cattle made their way to Miles City in 1999 after a research farm at
Washington State University was closed.
In crossing Wagyu cattle with Limousin cattle, MacNeil, colleague Lee
Alexander, and university partners created a genetic resource they can
tap for more clues about the genes that play a role in deposition of
fat and fatty acid composition.
Wheeler and his MARC colleagues, including Steven Shackelford and Mohammad
Koohmaraie, compared Wagyu to other breeds and found that they possess
carcass and meat-quality traits very similar to Angus when produced
in typical U.S. production systems. Wagyu cattle not destined to become
Kobe beef yield leaner carcasses than Angus and other British breeds,
but they also grow more slowly and less efficiently than other breeds.By
David Elstein and
Erin K. Peabody,
Agricultural Research Service Information Staff.
This research is part of Food Animal Production, an ARS National
Program (#101) described on the World Wide Web at www.nps.ars.usda.gov.
Michael D. MacNeil
is with the USDA-ARS Fort Keogh
Livestock and Range Research Laboratory, 243 Fort Keogh Rd., Miles
City, MT 59301; phone (406) 232-8213, fax (406) 232-8209.
Timothy P.L. Smith
and Tommy L. Wheeler
are with the USDA-ARS Roman L. Hruska
U.S. Meat Animal Research Center, Spur 18D, Clay Center, NE 68933;
[Smith] phone (402) 762-4366, fax (402) 762-4390; [Wheeler] phone (402)
762-4229, fax (402) 762-4149.
"Can You Have Your Beef and Eat It Too?" was published
in the July
2004 issue of Agricultural Research magazine.