The foundation of muscling
Muscling begins at conception
by Sally Colby
There’s no question that consumers who purchase beef expect a high-quality eating experience. Dr. Jennifer Martin, associate professor of meat safety and quality at Colorado State University, discussed the role of muscle formation in beef cattle, which begins far in advance of a prime steak hitting the plate.
A high-quality beef eating experience for consumers varies widely. It might be a perfectly cooked steak, a brisket or a juicy burger. Martin said there’s science behind the beef grades, and that biology and physiology impact production, performance, carcass quality and consumer acceptance.
Several traits are associated with beef quality, including palatability or tenderness, juiciness and flavor. Consumers are also interested in appearance, including meat color and packaging. Other aspects such as price and production strategy play a role in consumer acceptance of beef as well. Certification programs including organic, grass fed, all-natural and humanely raised have value to many consumers. Sociocultural values are important and represent the product itself and the value the consumer places on specific attributes. Values such as animal welfare, sustainability issues and locally raised are important to many consumers.
However, palatability reigns as the number one factor for consumers. “We know palatability is important,” said Martin. “Consumers consistently tell us they want to have a good eating experience. We know consumers value tenderness, and consider it an essential trait. If the product is not tender, consumers won’t accept it. This isn’t new information for the beef industry, but one thing the industry has done well in response to that information is invest in improving tenderness. That’s why over 90% of steaks produced in the U.S., whether foodservice or retail, are considered tender or very tender.” The beef industry is also aware that flavor is equally important, and more than half of consumers surveyed said flavor is more important than tenderness. (Consumers placed the least value on juiciness.)
Since palatability is at the top of consumers’ lists in evaluating a beef eating experience, it’s worth understanding the biology behind it.
“If marbling is so highly correlated with a positive eating experience, why don’t we produce all prime beef?” said Martin. “Why don’t we shoot for the top marbling scores and try to produce as much high-marbled beef as we can? We do a pretty good job as an industry producing high quality beef carcasses.” The percentage of prime and choice carcasses has increased between 1991 and 2016.
Martin explained that high quality beef begins at the cellular level – from the cells in the developing embryo to the calf and the pregnant cow – and ends at the rail. “It’s easy to focus on the end product,” she said. “The carcass in the cooler or the calf in the feed yard and the variables we know will impact the carcass. Many of the variables that impact beef quality are impacted by the development of muscle, bone and connective tissue and fat. We also know those three attributes start as mesenchymal stem cells.”
High quality cattle begin with good skeletal structure – it’s difficult to build high yielding beef without a strong skeletal system. “Bones serve as levers for skeletal muscles,” said Martin. “Skeletal structures form prenatally. Bone is formed from the mesoderm layer during embryonic development, and at birth, bone content is relatively high – about two parts bone to one part lean. As the animal matures and accumulates more lean and fat tissue, bone content decreases proportionately.”
Factors such as cow nutrition, management and hormones can all influence post-natal skeletal development and bone growth. Functional use influences bone growth – bones grow as they’re used. Castration and estrogenic exposure can inhibit bone growth. “We know that good structural development lays the foundation for a strong muscular system,” said Martin. “We know that muscles and bones used more frequently tend to have more support for muscle growth.”
After a calf is born, post-natal changes influence skeleton and muscle. “We know skeletal growth occurs longitudinally,” she said. “Bones grow in length, not in girth or width. We only see width or girth in mature animals. We know longitudinal growth occurs at the epiphysial plates, or growth plates, through ossification. Bones are growing at the ends and continue to grow at the ends. We know the amount of bone growth depends on the rate of new cell production as well as the size of cells before they ossify. Eventually, bone growth will plateau.”
As bones grow longitudinally, muscle grows with them. “We know that a large frame size is usually associated with a faster rate of lean meat growth, so animals that have a high skeletal growth rate tend to deposit more lean muscle and tend to be later maturing than those with a smaller frame,” said Martin. “We see a variety of frame sizes in U.S. cattle, and that variety of frame sizes can give a good indication of what quality we can expect in the meat of that animal. Leaner cattle, leaner carcasses yield leaner beef, and tend to be later maturing.”
Meat science has shown that muscle development begins early in gestation. “In the first two months of gestation, we see the development of primary muscle cells,” said Martin. “In months two through eight of pregnancy, secondary muscle cells are formed and we see the majority of skeletal muscle formation. That means the majority of skeletal muscle formation occurs well before the animal is on the ground.”
The management of the cow, particularly in mid-gestation, is highly correlated with muscling. Poor nutrition during gestation can lead to light muscling and low yield. From birth, the calf exposed to poor prenatal nutrition has fewer muscle cells, which means less muscle to develop post-natally. “Post-natal growth occurs inside cells versus number of cells,” said Martin. “Management of cows during pregnancy goes a long way in helping to set these animals for high muscle, high yielding carcasses.”