Genetics, Environment Contribute to Woody Breast Condition

Researchers Nearing Solutions for Issue Affecting Producer Output, Profitability

More than 50 billion chickens enter the human food supply every year, and that number is expected to grow in the next decade to meet increasing food demand as world population continues to rise.

The industry has responded to that growing demand; in the last five years alone, world broiler meat production has risen from 86.76 to 92.47 million metric tons per year, according to the U.S. Department of Agriculture Foreign Agricultural Service. Chicken as a human protein source alone has grown by 80 percent in the last decade, much faster than beef or pork. That growth, however, has had some unintended consequences; including one that has, to this point, stymied the industry and led to promising research breakthroughs by Kemin.

To keep pace with growing demand, the poultry industry began making improvements to traditional breeds and genetics to yield growth levels that eclipse those in other livestock sectors. In the last 33 years, the industry has increased the size of the average broiler by 68 percent, according to Kemin Associate Research Scientist Farrah Phillips.

“Unfortunately, the increase in bird size – driven by increased demand – has led to the discovery of the woody breast condition (WBC),” Phillips says. She is a member of the team of researchers working to find a solution for the condition that causes some breast meat to take on a wooden texture, keeping it out of the human food supply and severely limiting the meat’s value for producers.

The Origins of Woody Breast Condition

Woody breast condition is a relatively new issue, appearing only in the last decade, says Kemin Technical Service Manager Karen Pollock. As researchers and genetic companies looked to increase overall production, they increased carcass size, and in doing so, created other issues in the process. Resolving those subsequent issues through further selective breeding then led to the rise of WBC.

“Genetic companies were pushing so hard to increase output, and when you push that hard in selecting something, you lose something else,” Pollock says. “Twenty years ago when they started selecting for more breast meat and bigger birds, birds started having leg problems because they couldn’t support themselves. Once they were selected for stronger legs, the poultry industry ended up with a bigger bird that could carry itself. But now the heart might have issues with providing enough blood flow to that extra breast tissue.”

“The selective breeding process is usually driven by one or two particular traits a producer is looking for,” adds Phillips. “Things like immune health or heartiness can get left behind accidentally because the industry focused on other traits. This happens all the time in selective breeding and you can’t blame the producer, because nobody knew this would happen. It was an unpredictable event.”

That process led to the genesis of WBC around a decade ago. In affected birds, inadequate vascularization causes free radical molecules to accumulate in the affected breast tissue, creating the oxidative stress to which the rise of WBC can be attributed. The result is tissue that’s physically harder, has less water-holding capacity (yielding drier chicken meat when cooked) and has more frequent fiber degeneration. Ultimately, a chicken breast that’s much less palatable to the consumer.

It’s virtually impossible to detect WBC until the animal is old enough that the condition is essentially irreversible in its damage to breast meat – the highest-value meat from a broiler. Also, because of the myriad of potential causes for the oxidative stress that leads to WBC, it has to-date been difficult to target through research and product development.

“If you picked up a normal chicken breast, it would bend or flop over,” says Phillips. “If you pick up a wooden breast, it would stick out in your hand, essentially, and would also have a less pleasant coloration to it. Sometimes, there’s mucousy tissue hanging on it. It’s really not visually appealing.”

Woody Breast Condition Research Priorities

While an experienced producer or researcher can spot WBC in an affected bird, it’s not easy. Part of the difficulty lies in its symptoms. Early research looked to connect physical symptoms to the condition’s incidence.

“There really isn’t an outward symptom,” Phillips says. “Chickens don’t display any type of discomfort or illness. There had been some investigation into wing contractility and flexibility, but research has not found a direct correlation between that and woody breast.”

Because there’s no known specific cause for woody breast and few physical symptoms in affected birds, there was little tangible direction for early research. Today, researchers are looking at different physiological processes for direction on better targeting their approach to the condition and the stressors that cause it.

“A lot of work is being done to analyze protein content, the quality of the meat and contents of muscle tissues,” Phillips says. “The problem with the type of data gleaned from that kind of analysis is that it’s really broad and very difficult to hone in on the underlying cause.”

There’s also genetic research underway to see what an animal’s pedigree has to do with its propensity toward woody breast. While Pollock says genetics is definitely one part of the equation, research has yet to uncover a genotype that is definitively more susceptible to WBC. Some breeds are more inclined to develop the condition, but Phillips suspects it has more to do with how genetics influence physiology, not the genotype alone.

“You can’t pin it down to genetic background,” says Phillips. “If it is an intrinsic genetic issue, then every bird of one breed would demonstrate the phenotype. Depending on the birds’ nutrition, how rapidly they grow and the conditions they’re grown in, you can get anywhere between 10 percent and 80 percent penetrance of woody breast. There are environmental factors that contribute to woody breast. It’s not just a genetic thing.”

Environment, Feed and Heat Stress

After genetics, some of the remaining pieces of the woody breast puzzle lie in the conditions under which chickens are raised. Because of the general demand for chicken, producers have accelerated growth through more intensive feeding rations in order to get birds market-ready quicker. Recent research from Auburn University shows that not only what the birds are fed, but how much and how rapidly they’re fed has a lot to do with the incidence of WBC.

So, wouldn’t backing off feed rations or feeding the birds slower help curtail the incidence of woody breast? It’s likely. But considering the demands on the industry as a whole, that’s not the most realistic outcome, Pollock says.

“When Auburn scientists presented their data, the industry said, ‘That’s great, now we know that by slowing down the birds, we can stop the condition from happening. Unfortunately, no growers are going to want to do that.’ Less weight means less money,” she says. “Woody breast is something that is related to big birds. Companies that grow six-pound birds versus nine-pound birds, for example, don’t have this problem. At six pounds, the bird still has the tools to provide all the nutrients its body is asking for, without the oxidative stress that leads to woody breast.”

The findings of recent trials conducted at Texas A&M University show that adding encapsulated butyric acid and zinc plus chromium – like that found in ButiPEARL^™ Z and KemTRACE^® Chromium by Kemin – might reduce WBC. Though it doesn’t altogether eliminate cases of woody breast, it lowers severity enough to avoid sharp quality declines.

“If you have a healthier gut, the bird is able to absorb more nutrients and antioxidants, and that can minimize the oxidative stress the bird is experiencing,” Pollock says

“We saw significant interactions between ButiPEARL Z and KemTRACE Chromium, cutting the incidence of woody breast compared to the control group,” Pollock says of the recent research, adding birds with mild cases of woody breast can often still enter the human food chain as unaffected birds. “When we looked at ButiPEARL Z only, we saw that it significantly decreased the percentage of severe and moderate woody breast scores and significantly increased the percentage of mild woody breast scores.”

Chicken Industry Implications

Woody breast can be avoided by making flock management and production changes, like slowing feeding and extending the amount of time between birth and harvest for integration into the food supply. Many of those changes, however, would mean slowing production and cutting the efficiencies the industry has created, reducing profits.

Moving forward, Pollock says research needs to recognize the necessities the chicken industry faces as a broader context for how new treatments for WBC are developed and taken to the marketplace. Ultimately, it’s about meeting consumer demand, growing the industry and finding a solution for the woody breast problem.

“There’s a market for big birds, and the industry knows that. They won’t give up that market,” says Pollock. “Given that situation, what can we do in feeding the birds so they shift away from severe woody breast? We have trials running and are working to validate our findings.”

“The industry must keep up with demand, so we have to find something to help them lose less money,” adds Pollock. “Genetics can reduce incidence, but it takes time. Everyone is excited to find answers, and it looks promising. The stakes are so high that we can’t move forward with just one study, however. We have to be really certain of how we are proceeding and finding the right answers.”

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