Green muscle disease is a condition where a specific chest muscle in chickens dies and turns green due to restricted blood flow. Formally called deep pectoral myopathy (DPM), it affects the small, inner breast muscle, the one sold as the “tenderloin” at the grocery store. The condition is one of the most common muscle disorders found on modern poultry processing lines, though it poses no food safety risk to humans.
Which Muscle Is Affected and Why
Chickens have two main breast muscles on each side. The large outer one is the breast fillet most people are familiar with. Tucked underneath it is a smaller muscle called the supracoracoideus, better known as the tenderloin. This deeper muscle is responsible for the upstroke of the wing during flapping.
The problem comes down to anatomy. The tenderloin sits in a tight compartment, sandwiched between the large breast muscle above it and the keel bone (breastbone) below. A tough sheet of connective tissue called fascia wraps around it. In modern broiler chickens, which have been bred for massive breast muscle growth, this compartment has very little room to spare. When the tenderloin swells from sudden exertion, the surrounding fascia cannot stretch to accommodate it. Blood flow gets cut off, starving the muscle of oxygen in a process similar to compartment syndrome in humans.
Without blood supply, the muscle tissue dies. In the early stages, the dead muscle looks pink or reddish, resembling a bruise. Over time, as degradation products build up and the tissue breaks down further, it turns a distinctive grayish-green color, which is how the condition got its common name.
What Triggers It
The single biggest trigger is vigorous wing flapping. Any event that causes a heavy broiler chicken to flap its wings repeatedly can set off the chain of swelling and blood flow restriction. In a controlled study, researchers induced flapping by raising and lowering broilers a short distance. Birds that experienced 10 rounds of flapping developed the condition in 7% of cases. At 20 rounds, the rate jumped to 33%. At 25 rounds, 56% of the birds were affected. Birds that didn’t flap, or flapped only five times, showed no signs of the disease at all.
On a commercial farm, common triggers include anything that startles birds into flapping: sudden loud noises, bright flashes of light, catching and handling during transport, or disturbances from equipment or predators. Even routine activities like moving through a barn can cause enough panic-flapping in a dense flock to trigger cases.
Which Birds Are Most at Risk
Heavier, faster-growing broiler breeds are far more susceptible. Their breast muscles are disproportionately large relative to the blood supply and connective tissue compartment they sit in. The condition is especially common in roaster chickens, which are grown to higher market weights than standard broilers. Interestingly, sex and moderate differences in body weight don’t seem to matter much. In the wing-flapping study, a 0.4 kg weight difference between groups had no effect on whether birds developed the condition.
The age of the bird also plays a role. Older, heavier birds with more developed breast muscles have less room in that tight compartment and are more vulnerable to ischemia when the muscle swells.
How It Looks During Processing
Green muscle disease is almost never detected in live birds. The affected tenderloin is hidden beneath the large breast muscle, and the condition doesn’t visibly affect the chicken’s health or behavior. It only becomes apparent when carcasses are cut up and deboned at the processing plant.
What processors find ranges from a pinkish, hemorrhage-like appearance in early-stage cases to a fully necrotic, grayish-green mass in advanced ones. In severe cases, the dead muscle may be surrounded by thick, gelatinous scar tissue that adheres to the surrounding breast meat. In a study of roaster chickens, the average rate of affected carcasses was about 0.84%, but that average hides wide variation. Individual flocks ranged from 0% all the way up to 16.7%.
Is the Meat Safe to Eat?
Yes. According to Hong Kong’s Centre for Food Safety, the condition is not caused by any infection or harmful substance and carries no food safety concern. The issue is purely cosmetic. A green, necrotic tenderloin is unappetizing and would be rejected by consumers, so affected tenderloins are discarded during processing. The rest of the carcass, including the large breast fillet directly above the damaged tenderloin, is unaffected and safe.
If you’re buying a whole chicken or bone-in breast at the store, there’s a small chance you could encounter a greenish tenderloin when you break it down at home. It won’t make you sick, but you’d want to trim and discard the discolored portion.
How the Industry Reduces It
Since wing flapping is the direct trigger, prevention centers on keeping birds calm. Commercial farms use carefully managed lighting programs to minimize startling. A typical approach involves bright light (around 40 lux) for the first week of life, then gradually reducing intensity to as low as 10 lux as birds grow. Dimmer lighting keeps birds calmer and reduces sudden flapping episodes. Photoperiods are also adjusted, moving from near-constant light in the first week to around 18 hours of light and 6 hours of darkness afterward, which encourages more natural rest cycles.
Stocking density matters too. Overcrowded birds are more likely to panic and flap when disturbed. European guidelines recommend keeping density at or below 29 to 32 kg per square meter. Gentle handling during catching and transport, reducing sudden noises, and minimizing disturbances in the barn all help lower the incidence. None of these measures eliminate the problem entirely, because the fundamental vulnerability is built into the anatomy of modern high-yield broiler breeds, but they can keep flock-level rates low.
Connection to Other Breast Meat Problems
Green muscle disease shares some underlying biology with two other conditions familiar to the poultry industry: white striping and woody breast. All three involve damage to breast muscle tissue, and microscopic examination reveals similar patterns of injury, including restricted blood flow, fiber damage, and scar tissue buildup. In woody breast cases, researchers have found extensive fibrosis where damaged muscle fibers are replaced by collagen and irregular new blood vessels, a repair process that leaves the meat tough and rubbery rather than green.
The common thread is that modern broiler genetics have pushed breast muscle growth beyond what the bird’s connective tissue and blood supply can fully support. Green muscle disease is the most dramatic visual example, but it’s part of a broader set of muscle quality challenges the industry continues to manage.