How to Recognize & Prevent Muscle Diseases in Poultry
Cornish Crosses and Breast Myopathies
Three conditions found in the breast meat of industrially grown Cornish cross broilers are of major concern to the poultry industry, but also can be disconcerting for anyone who raises heavy-breasted broilers for the family table. These myopathies, or muscle diseases, are known respectively as green muscle, white striping and wooden breast. None of the three conditions is evident until a broiler is slaughtered and its breast meat examined.
Green muscle is nothing new, being first recognized in 1975, but white striping and wooden breast weren’t identified until around 2012 and didn’t grab major media attention until last spring. All three conditions are associated with industrial broiler strains bred for excessively large breast muscles, which can be as much as 25 percent of a bird’s total body weight.
Even if you choose to raise an industrial broiler strain for homegrown meat, these breast myopathies may be avoided through good management and proper nutrition. If you do encounter any of these conditions, the following information will help you identify the problem and determine how to prevent it in the future.
Green muscle was first identified in broad-breasted turkeys. Among industrial Cornish cross broilers, it occurs less often in pullets than in heavier cockerels. It affects the tender strip of meat that, when the breast is removed from the bone, easily separates from the main part of the breast. Because the tender is deep within the breast (or pectoral) muscle, green muscle disease is technically known as deep pectoral myopathy.
The deep pectoral is the muscle a chicken uses to raise its wing. This muscle is surrounded by a tough, inflexible sheath and is further confined by the breast bone below and the larger breast muscle above. When a broiler flaps its wings, blood flow increases to the deep pectoral, supplying the muscle with needed oxygen. This increased blood flow causes the muscle to expand until it becomes restricted within its tight chamber, which then blocks the flow of blood.
If the wing flapping continues, the tender is deprived of oxygen. The muscle bruises, atrophies and dies. Depending on how long before slaughter the wing-flapping incident occurred, the bird’s tenders may appear bloody or yellowish, or turn an unappetizing green color.
Heavier broilers, such as might be raised for roasting, are more likely to be affected than broilers harvested at the fryer stage. Broilers raised in cool weather grow faster and therefore are more likely to be affected than those grown in warm months. Green muscle can be a bigger issue in pastured Cornish cross broilers than in confined broilers, because outdoor chickens are subject to a greater variety of scary wing-flapping experiences — such as prowling predators, large birds flying overhead, or sudden loud noises from passing people or vehicles.
Since green muscle disease produces no outwardly visible signs, no treatment is possible. Prevention involves taking measures to ensure heavy-breasted broilers are not startled into excessive wing flapping. Teach small children and household pets not to chase broilers. Do not catch or carry the birds by their wings or legs. Do not provide perches, from which birds would fly down while flapping their wings.
The cause of white striping has so far baffled the poultry industry. Like green muscle disease, white striping mainly affects industrial strain broilers grown to heavier weights. It appears as white lines, consists of fat tissue, and runs parallel to the breast muscle fibers. White striping can also affect other muscles, most notably the thighs, and occurs in heavy breasted turkeys as well as in Cornish cross broilers.
Breast meat with white striping is lower in protein and higher in fat than normal breast meat. It does not as readily absorb marinades, and tends to lose more moisture when cooked compared to normal chicken meat.
While white striping appears to be a form of muscular dystrophy, it is unrelated to white muscle disease that occurs in calves, lambs and goat kids. Unlike white muscle disease, white striping cannot be prevented by increasing vitamin E in the chickens’ diet.
White striping is associated with rapid growth rate, especially in broilers that are fed a high calorie diet to encourage faster growth. Current speculation is that the resulting rapid increase in breast size reduces the ability of oxygen and nutrients to adequately supply the muscle, and also reduces the ability of muscle cells to remove metabolic waste. White striping may be prevented by avoiding high energy feeds or by restricting feed intake, rather than making feed available 24/7.
Wooden breast is the latest myopathy to appear on the poultry scene. It occurs as a separate condition from white striping, although the two disorders may appear together. Wooden breast is a stiffening of the breast muscle, typically appearing in the middle of the breast fillet as hard, pale, bulging, wood-like fibers that make the meat unpleasant to chew
Breast meat affected with this condition absorbs marinades less readily than meat affected by white striping, and loses more moisture during cooking. The high moisture loss results in tougher meat at the table.
As with white striping, the exact cause of wooden breast is not yet known Apparently it is the result of muscle fiber degeneration and subsequent scarring. Like other breast myopathies, wooden breast is associated with unusually rapid growth. Prevention is the same as for white striping.
None of these conditions has been attributed to any known infectious agent. Instead, they appear to result from malfunctioning metabolism in the muscle cells. A recent report in the journal Poultry Science concludes that breast meat myopathies are marginally related to genetics and may be controlled through good management and nutrition. For those of us who grow our own chicken meat, it means we can avoid these myopathies, even if we choose to raise one of the Cornish cross strains developed for industrial production.
Another option is to raise colored Cornish hybrids, an industrial creation popular among proponents of pastured broilers. Some common trade names are: Black Broiler, Color Yield, Colored Range, Freedom Ranger, Kosher King, Redbro, Red Broiler, and Silver Cross. Most strains have red plumage, but they also come in black, gray, or barred — anything but white. Their colored feathers make them less attractive to predators, especially hawks, but more difficult to pluck clean. Colored Cornish broilers grow more slowly than white hybrids, so they are not afflicted by any of the breast meat myopathies. A further result of their slower growth is that their meat is more flavorful than that of the faster growing white hybrids.
A third option appeals to those of us who keep a standard or heritage breed for eggs. Nothing is wrong with raising surplus cockerels for the freezer. Heritage breeds with the greatest potential as broilers are: Delaware, New Hampshire, Plymouth Rock, and Wyandotte. Naked Necks aren’t a heritage breed, but they do make good meat birds and have sparse plumage that can be an advantage at plucking time. All these breeds are good foragers and have a moderate to slow growth rate. Compared to Cornish hybrids — white or colored — they have thinner breasts and more dark meat, and the meat has a stronger chicken flavor. Plus, of course, they do not incur the Big Three breast myopathies.
Regardless of the breed or hybrid you choose to raise for meat, by properly managing your homegrown broilers to minimize stress and by providing them with a healthful well-balanced diet, you can enjoy the best tasting chicken on earth. And you needn’t be concerned about the possibility of serving green tenders or woody breasts at your family table.
Gail Damerow is author of The Chicken Health Handbook which, along with her several other books on raising chickens, is available from our bookstore at www.CountrysideNetwork.com/shop/.