By Tom Tabler, Ph.D. Extension Professor, Mississippi State University Extension Service, Poultry Science Department.

This condition isn’t new and it can occur at any age or weight. GMD is not to be confused with woody breast, which has been featured in a number of articles in recent years and is distinctly different.

GMD is closely associated with heavier weight birds grown for the debone market. As the percentage of birds grown to heavier weights for deboning has increased, so has the incidence of GMD showing up at processing plants.

This degenerative muscle disease affects the minor pectoral muscles - the tenders - of poultry. Unfortunately, it’s not detected until birds are deboned at processing and it results in condemnations.

If a bird with GMD isn’t deboned and is sold instead as a whole carcass or as parts, the problem doesn’t show up until the chicken is on someone’s dinner table. There’s no infectious agent involved and no public health concern, but who wants to eat green chicken?

It’s costly

GMD is costly. Several years ago, it was projected that for a plant processing 1 million head of seven- to eight-pound broilers per week, losses from GMD would be about a ton of condemned tenders per week and a similar weight of fillet trimmings each week, resulting in an economic loss of $7,000 per week.[2]

Actual numbers are likely higher today because many birds may be processed at nine or more pounds live weight, and many plants are now processing at least 1.25 million head per week.

Wing flapping = GMD

It’s believed GMD results from contraction of the breast fillet and tender that control up-and-down wing movement. Expansion of the tender is difficult because of its location. The tender is located between the breast bone and the large breast fillet, and it’s encased in a fibrous sheath that allows little room for increased muscle volume.

As the bird flaps its wings, the tender’s muscle volume tries to increase but can’t. Blood supply is cut off, and the result is oxygen deficiency that causes localised death of cells and tissues.

GMD can occur after one serious episode of wing flapping, or it can occur cumulatively due to multiple episodes. It’s probably more common in heavier weight birds because heavy fillets press on the tender, making it more difficult for the tender to increase muscle volume.

An important cause of GMD, therefore, is anything that causes increased bird activity that leads to wing flapping. Growers disturbing birds by moving too fast through the house, bright or intense lighting, excessive noise or rough handling of birds during catching as well as running loud equipment in or near the poultry house are all factors that can lead to increased bird activity and, ultimately, GMD.

Colourful stages

Tenders in chickens with GMD don’t turn green immediately. I’ve seen every stage of the condition, from the early beginnings when the predominant colour is red, to the final stages when one or both tenders may be all or partially green.

For the first 48 hours or so immediately after the initial event, the tender appears red, which is due to ruptured blood vessels. After 48 hours and for the next few days, the affected tender takes on a light pink colour that progresses gradually to dark purple or plum.

As more time passes, maybe a week or longer, the tender finally turns to green, the colour for which it is named. The green colour is the result of the gradual breakdown of haemoglobin and myoglobin in the damaged muscle tissue. I consider it similar to walking into the drop-down bumper hitch on the back of my pickup. The soon-to-be bruise is red for the first day or so, then eventually blue, purple, yellow and finally green a few days later. While the causes may be different, the results are pretty similar - ruptured blood vessels and damaged tissue.

Adjust management

While a host of genetic, physiological and farm-management factors likely play a role in the occurrence of GMD, the key to controlling the problem appears to be management that limits wing flapping.

Birds should be disturbed as little as possible. Note that I did not say to neglect your flock! You still must regularly check birds and monitor air quality, ventilation, temperature, ammonia levels and litter conditions, and mortalities need to be removed. However, when working in or around the houses, move slowly and use extra care, especially near migration fences. Birds tend to pile up at migration fences, more so if they are pushed too fast, and piling results in increased wing flapping.

Noise levels inside and outside of poultry houses need to be kept to a minimum since loud noise frightens birds and increases wing flapping. This may mean putting off mowing around houses a few extra days, but that’s better than panicking birds.

Other ways to minimise bird activity is by maintaining low light levels and making sure you don’t run out of feed, since hungry birds become very active when they have access to feed again.

Be extra careful preparing the house for catching. Feeder and drinker lines must be winched into the ceiling for catching, which means increased noise levels from the drill and winches. Proceed slowly and as quietly as realistically possible since extra activity and movement of lines above the chickens’ heads will make them nervous and flighty and more prone to wing flapping. They are afraid of movement above their heads because it’s similar to being attacked by aerial predators.

In short, GMD appears to be closely tied to farm management, unlike diseases that result from some type of infectious agent. Management that lessens or minimises wing flapping throughout the flock appears to be the best defence we currently have against GMD.

‘Heads up’ to processing

Anytime those of us on the live-production side of the poultry business know birds to be marketed may have a problem, it’s a good idea to give the processing plant a “heads up” instead of assuming it’s the plant’s problem.

This would include GMD, which can be suspected if live production knows something happened before processing to cause an undue amount of wing flapping. The processing plant may want to adjust the speed of the cone line for deboning or add an extra worker or two.

Conversely, it should be the same on the processing side. If the plant sees a high incidence of GMD, the live-side folks need to know about it so they can initiate a search to find the cause and prevent it in the future. Maybe a grower was bush-hogging next to the poultry house a few days before processing or maybe the lighting program was changed, leading to increased bird activity and wing flapping.

Communication on both sides, and a better understanding and appreciation of what the other side is dealing with, will make things run smoother for everyone and help the industry manage problems like GMD at processing.

References:

1. US poultry production set to rise 3%. Poultry World. February 9, 2018. http://www.poultryworld.net/Meat/Articles/2018/2/US-poultry-production-set-to-rise-3-246723E/. Accessed March 14, 2018.

2. Finding answers to ‘green muscle disease.” WATTAGNet.com. April 20, 2011. https://www.wattagnet.com/articles/8761-finding-answers-to-green-muscle-disease. Accessed March 18, 2018.