Wooden Breast, White Striping, and Spaghetti Meat Myopathies in Poultry
"Wooden breast," "white striping," and "spaghetti meat" myopathies (pectoralis major muscle myopathies) occur in commercial, rapid-growth, high-breast-yield broiler chickens worldwide.
These myopathies affect primarily the superficial pectoral muscle (pectoralis major).
Affected chickens do not exhibit clinical signs.
The macroscopic appearance of these myopathies differs, with some overlap:
Wooden breast myopathy is characterized by firm, pale muscles (see wooden breast image).
White striping myopathy is characterized by white striations in the muscle parallel to the fiber direction.
Spaghetti meat myopathy is characterized by soft, friable muscles.
Courtesy of Dr. T. A. Abdul-Aziz.
These lesions are more prominent in the anterior and middle part of the pectoral muscles. Edema and occasionally hemorrhage can expand the fascia overlying the muscles in severely affected broilers with wooden breast myopathy.
Although the macroscopic appearance differs, microscopic lesions of these three genetic myopathies are similar in appearance, suggesting the possibility of a common pathogenesis. Microscopically, polyphasic myodegeneration and regeneration, interstitial fibrosis, adipocyte accumulation, and perivascular lymphocytic infiltration are present.
The pathogenesis of these myopathies in poultry is incompletely understood. Selection for fast growth rate and increased total breast meat yield has affected muscle morphology with an increase in myofiber diameter, decrease in connective tissue and blood supply, and altered muscle metabolism. These changes might result in increased myofiber susceptibility to degeneration, necrosis, and limited regenerative capacity, ultimately predisposing the birds to myopathy.
Wooden breast, white striping, and spaghetti meat myopathies result in substantial economic losses in the poultry industry, as a result of decreased meat quality and condemnation of affected muscles.
Glycogen Storage Myopathy in Poultry
Type II glycogen storage disease (acid maltase deficiency, Pompe disease) has been reported in Japanese quail (Coturnix japonica).
Images courtesy of Dr. H. J. Barnes.
Clinical signs appear between 4 and 6 weeks of age, and affected quail show progressive myopathy with either inability or decreased ability to lift their wings, fly, or right themselves after being placed on their back (flip test).
In this disorder, excessive glycogen is deposited in skeletal muscle, cardiac muscle, and smooth muscle, as well as in the brain and spinal cord (see glycogen storage disease image). Both red and white muscle are affected, but lesions are more pronounced in the pectoralis superficialis (white muscle).
Key Points
Wooden breast, white striping, and spaghetti meat myopathies affect the pectoralis major muscle of commercial high-breast-yield broiler chickens.
Pale and firm muscles, white striations parallel to muscle fiber direction, and soft, friable muscles are observed in wooden breast, white striping, and spaghetti meat myopathies, respectively.
These myopathies result in substantial economic losses.
For More Information
Saif YM, Swayne DE, Pantin-Jackwood MJ, et al. Emerging diseases and diseases of complex or unknown etiology. In: Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley Blackwell; 2020:1383-1410.
