A myopathy affecting the pectoralis major muscle of the commercial broiler has emerged creating remarkable economic losses as well as a potential welfare problem of the birds. We here describe the macroscopic and histologic lesions of this myopathy within 10 pectoralis major muscles of 5- to 6-week-old broilers in Finland. Following macroscopic evaluation and palpation of the muscles, a tissue sample of each was fixed in formalin, processed for histology, and histologically evaluated. The muscles that were macroscopically hard, outbulging, pale, and often accompanied with white striping histologically exhibited moderate to severe polyphasic myodegeneration with regeneration as well as a variable amount of interstitial connective tissue accumulation or fibrosis. All affected cases also exhibited perivenular lymphocyte accumulation. The etiology of this myodegenerative lesion remains yet open. Polyphasic myodegeneration is associated with several previously known etiologies, but palpatory hardness focusing on the pectoralis major, together with perivenular lymphocytes, has not been described in relation to them. The results of this study provide the pathological basis for further studies concerning the etiology of the currently described myopathy.

https://journals.sagepub.com/doi/pdf/10.1177/0300985813497488

Myodegeneration with fibrosis and regeneration in the pectoralis major muscle of broilers.

During the past few decades there has been a notable increase in the demand for poultry meat due to its low cost, good nutritional profile and suitability for further processing. Moreover, current ...

Meat quality in fast-growing broiler chickens

White striping and woody breast myopathies in the modern poultry industry: a review

One of the consequences of intense genetic selection for growth of poultry is the recent appearance of abnormalities in chicken breast muscles, such as white striping (characterised by superficial white striations) and wooden breast (characterised by pale and bulged areas with substantial hardness). The aim of this study was to evaluate the quality traits of chicken fillets affected by white striping and wooden breast abnormalities. In two replications, 192 fillets were divided into the following four classes: normal (n=48; absence of any visual defects), white striping (n=48, presence of white striations), wooden breast (n=48; diffusely presence of hardened areas) and white striping/wooden breast (n=48; fillets affected by both abnormalities). Morphology, raw meat texture and technological properties were assessed in both unprocessed (pH, colour, drip loss, cooking loss and cooked meat shear force) and marinated meat (marinade uptake, purge loss, cooking loss and cooked meat shear force). Fillets affected by white striping, wooden breast or both abnormalities exhibited higher breast weights compared with normal fillets (305.5, 298.7, 318.3 and 244.7 g, respectively; P<0.001). Wooden breast, either alone or in combination with white striping, was associated with a significant (P<0.001) increase of fillet thickness in the caudal area and raw meat hardness compared with both normal and the white striping abnormality, for which there was no difference. Overall, the occurrence of the individual and combined white striping and wooden breast abnormalities resulted in substantial reduction in the quality of breast meat, although these abnormalities are associated with distinct characteristics. Wooden breast fillets showed lower marinade uptake and higher cooking losses than white-striped fillets for both unprocessed and marinated meats. On the other hand, white-striped fillets showed a moderate decline in marinade and cooking yield. Fillets affected by both abnormalities had the highest (P<0.001) ultimate pH values. In contrast, the effects on colour of raw and cooked meat, drip loss, purge loss and cooked meat shear force were negligible or relatively low and of little practical importance. Thus, the presence of white striping and wooden breast abnormalities impair not only breast meat appearance but also the quality of both raw and marinated meats mainly by reducing water holding/binding abilities.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/9503CB839FA75E0CFBAC3F8645D6FEE0/S175173111400295Xa.pdf/div-class-title-implications-of-white-striping-and-wooden-breast-abnormalities-on-quality-traits-of-raw-and-marinated-chicken-meat-div.pdf

Implications of white striping and wooden breast abnormalities on quality traits of raw and marinated chicken meat.

Ten years ago, the occurrence of macroscopic defects in breasts muscles from fast-growing broilers challenged producers and animal scientists to label and characterize myopathies wholly unknown. The distinctive white striations in breasts affected by white striping disorder, the presence of out-bulging and pale areas of hardened consistency in the so-called wooden breast, and the separation of the fiber bundles in breasts labelled as spaghetti meat, made these myopathies easily identified in chicken carcasses. Yet, the high incidence of these myopathies and the increasing concern by producers and retailers led to an unprecedented flood of questions on the causes and consequences of these abnormal chicken breasts. This review comprehensively collects the most relevant information from studies aimed to understand the pathological mechanisms of these myopathies, their physicochemical and histological characterization and their impact on meat quality and consumer's preferences. Today, it is known that the occurrence is linked to fast-growth rates of the birds and their large breast muscles. The muscle hypertrophy along with an unbalanced growth of supportive connective tissue leads to a compromised blood supply and hypoxia. The occurrence of oxidative stress and mitochondrial dysfunction leads to lipidosis, fibrosis, and overall myodegeneration. Along with the altered appearance, breast muscles affected by the myopathies display poor technological properties, impaired texture properties, and reduced nutritional value. As consumer's awareness on the occurrence of these abnormalities and the concerns on animal welfare arise, efforts are made to inhibit the onset of the myopathies or alleviate the severity of the symptoms. The lack of fully effective dietary strategies leads scientists to propose whether "slow" production systems may alternatively provide with poultry meat free of these myopathies.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/1541-4337.12431

D. P. Shaw

Papers

Pathological changes associated with white striping in broiler breast muscles