Year: 2018
Type: dissertation
Abstract: Abnormally hard breast fillet consistency began to emerge in commercial broiler chickens approximately around 2010. Due to the remarkable muscle hardness, the condition acquired a vernacular name ‘wooden breast myopathy’ (WB). This thesis includes studies of WB morphology and pathogenesis on field samples obtained from slaughterhouses in 2012 and experimental rearing studies of broilers, conducted in 2012 and 2014. The first substudy of this thesis describes the chronic morphology of WB and resulted in the first peer-reviewed publication on WB. The second and third substudies include further analyses on the morphology and pathogenesis of WB. This work characterizes WB as an abnormally firm muscle consistency that is restricted to the pectoralis major muscle in broiler chickens. Additional macroscopic features include pale color, outbulging appearance, occasional hemorrhage and a layer of clear fluid on the muscle surface. WB starts to develop after two weeks of age at the earliest and typically proceeds into a chronic myodegeneration in three to four weeks of age. The lesion begins focally and typically develops into a diffuse lesion that involves the major pectoral muscle completely. Microscopically, WB manifests as a polyphasic myodegenerative disease. This rules out single injuries to the muscle tissue as etiologies for wooden breast myopathy. Ongoing myodegeneration is accompanied by regeneration, and at chronic stages prominent secondary changes such as fibrosis develop. Lymphocytic phlebitis is strongly associated with the myodegeneration, but its role in the pathogenesis of wooden breast is currently disputable. The restricted location of the wooden breast lesion in the pectoralis major muscle distinguishes it from several other myodegenerative diseases that widely affect the skeletal muscle system and often the cardiac and smooth muscle systems too. Other skeletal muscles, such as thigh or dorsal muscles, may occasionally exhibit wooden breast-like lesions, but the syndrome primarily affects the major pectoralis muscle. Relatively reduced microvessel density contributes to the development of wooden breast myopathy. Either the affected birds initially exhibit lower capillary densities, compared to the birds that never succumb to wooden breast, or a relative reduction in the vascular supply,which occurs before the initiation of the degenerative lesion. Decreased dietary selenium does not affect the prevalence of wooden breast myopathy. The morphology of polyphasic myodegeneration renders selenium deficiency as one possible causative factor for wooden breast myopathy, but decreased selenium content in the diet had no effect on the prevalence of wooden breast myopathy in our experimental rearing studies
Source: Työväentutkimus Vuosikirja
Author: Sihvo, Hanna-Kaisa
Institution: University of Helsinki
Language: English
Subfield: Animal Science and Zoology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2912690145