Broiler breast myopathies: causative mechanisms and connective tissue involvement

A remarkable post-hatch hypertrophic growth of the fibers represents a hallmark of the Pectoralis major muscles of broiler chickens belonging to fast-growing and high breast yield genotypes. This increase in myofibers diameter is negatively correlated to the connective tissue spacing both at perimysial and endomysial level which however are essential for proper muscle functioning and vascularization. Therefore, considering the importance of the extracellular matrix environment, the abovementioned diminished connective tissue spaces together with an enlargement of the myofibers have been associated with a progressive overproduction of fibrillar collagens and proteoglycans resulting in a fibrotic organization of the connective tissue and, ultimately, to the development of myopathic conditions in broilers including the wooden breast and white striping abnormalities. The worldwide emergence of these myopathies paved the way for a wealth of studies performed over the past fifteen years with the aim of characterizing the affected breasts as well as to identify the putative etiologies and molecular mechanisms underlying their occurrence. Despite the comprehensive knowledge gained concerning these conditions, which have multifaced and interconnected origins, their exact causative mechanisms remain not fully understood. Therefore, this speech will provide an update of the putative phenomena playing a key role in the pathogenesis of the growth-related myopathies in broilers by considering the structural arrangement of the connective tissue as the root for describing the microscopic alterations associated to their onset.