University of Delaware researchers in the College of Agriculture and Natural Resources have made a new discovery in their work on wooden breast syndrome in chickens. The UD team found white blood cells filled with fat surrounding broiler chickens’ veins and showing signs of swelling are key contributing factors to this muscle degeneration disease in these birds that can ultimately affect their meat quality.
Wooden breast syndrome disease is characterized by firm, yellowish breast muscle and is estimated to affect up to 5 percent of a given flock of broiler chickens, rendering meat from those birds tough and chewy — and therefore unmarketable.
The disease may cost U.S. poultry farmers at least $200 million annually. The cause is unknown, but there is speculation the disease results from genetically breeding chickens to have larger breast muscle mass.
In the new research published in Scientific Reports, UD researchers in the Department of Animal and Food Sciences used an emerging technique called spatial transcriptomics to obtain detailed information on what the genes in individual cell types are doing within chicken muscle tissue.
The researchers could see what specific information was encoded in each of the genes in chickens’ various cells. They found white blood cells called lipid-laden macrophages, or “foam cells,” close to chickens’ veins, which are the key cells responsible for altering the breakdown and storage of fats at the onset of wooden breast syndrome.
The findings could help better understand a disease that has puzzled the agricultural industry.
But spatial transcriptomics isn’t only for the birds. What the researchers have discovered with spatial transcriptomics could help advance studies of obesity in humans.
An economic and welfare problem
Chickens with wooden breast syndrome are easy to spot. They often have trouble walking, and their wings are not as flexible, said Behnam Abasht, a professor of animal genetics at UD’s College of Agriculture and Natural Resources.
“This is a very big economic problem with some welfare aspects involved with this disease,” Abasht said. “Any solution you find that could improve the health of a chicken and also economically help poultry producers would have a big impact.”
Additionally, when chickens don’t have good wing mobility, they may fall over while walking and won’t be able to use their wings to get back up. Erin Brannick, a UD associate professor and veterinary anatomic pathologist, explained that researchers have seen issues where birds will lie down and not want to move. That immobility makes them susceptible to other diseases.
“We really look at this twofold. We want to keep our meat products safe, healthy and meeting consumer demands,” Brannick said. “At the same time, we want to make sure that we’re working in the interest of bird health and making sure that they’re happy, healthy, able to move around and do what a normal broiler chicken would do in eating and intermingling with other birds.”
Abasht and Brannick have collaborated on wooden breast syndrome research for over a decade. Ziqing Wang, now a UD alumna and the first author of the paper, worked on the research as a doctoral candidate under the guidance of Abasht from 2019 through August 2023. Paul Khondowe, lecturer and researcher at the University of Zambia, joined the team as a Fulbright Visiting Scholar hosted by the Abasht laboratory.
Decoding gene transcripts
In this latest research, the team examined muscle tissue from three 23-day-old broiler chickens randomly chosen from a UD chicken house.
The researchers froze samples of their muscle tissue and then sliced the hardened tissue into very thin sheets. They took images and examined the samples microscopically for signs of disease while they also analyzed the genes in the muscle tissue. One of the three samples was confirmed to have wooden breast syndrome. In that sample, the researchers found fatty white blood cells, or lipid-laden macrophages, close to the chicken’s veins. They also found foam cells in the two seemingly unaffected samples, indicating that they were beginning to develop wooden breast syndrome.
“Because the lipid-laden macrophages are so close to the veins, it’s possible when they grow in size or quantity it could cause vein occlusion,” Wang said. “The veins are pushed. There’s not enough blood going around, eventually leading to vein inflammation.”
Wang said this could also suggest that lipids coming from the veins “are not properly used.” The lipids could even be triggering inflammation in a chicken’s breast.
The new findings advance the team’s previous findings that an enzyme crucial for fat metabolism may be contributing to wooden breast syndrome.
“Our current findings further supported the importance of a previously identified key-playing gene in wooden breast syndrome, and demonstrated the specific cell types where this gene is expressed,” Wang said.
To the best of the team’s knowledge, Wang said, this work is likely the first one in the world using spatial transcriptomics to study the functional role of specific cell types within the tissue during the development of wooden breast syndrome in chickens, combining the process of turning genes into proteins and RNA and studying tissue anatomy, during the development of wooden breast syndrome in chickens.
“We’re trying to understand this disease better and to maybe try to think of better ways to control this disease, future breeding strategies,” Wang said. “We’re trying to understand what’s really happening.”
Through the research, the team also identified potential wooden breast-specific biomarkers, which could help identify and diagnose the disease early.
“It’s important because it could be specific to this disease or to muscle damage, so that could potentially be further studied,” Wang said. “It could be important for using other techniques to either confirm it or just to further study what these particular genes are doing in the muscle.”
Finding a solution
So what is changing metabolically in chickens that do have wooden breast syndrome compared to chickens that don’t have it? In the long term, that is precisely what the research team would like to uncover. With that information, the team could work its way backward and solve the problem of reducing the prevalence of wooden breast syndrome in chicken flocks.
“If we can delay when the disease starts and how severe it gets, that would be an incredible achievement,” Brannick said.
Brannick said some chicken companies have already begun making changes to their breeding practices, taking a different approach to what chickens’ breast muscles should be like.
“Everything new that we learn about this disease will help us reduce how bad it gets or how many birds are affected in the future,” Brannick said. “All of that helps us make more chicken that more people want to eat. It also keeps those birds healthy and happy while they’re growing.”
The research could also have implications for understanding human diseases. Abasht sees applications to the study of obesity, for example.
Lipid-laden macrophages in chicken breast muscles happen where there is a lot of fat in the tissue. This is kind of like what happens in obese people and in the inflammation that comes from fatty deposits in human arteries when fat and cholesterol build up inside of artery walls.
“A breakthrough in animal disease research could create pathways for breakthroughs in human disease research,” Abasht said. “Our study unlocks the potential for other avenues of research.”
»Related: Understanding ‘spaghetti meat’ — a poultry muscular abnormality
