A histologic and ultrastructural study of wooden breast disease in modern broiler chickens

Abstract Text: Wooden Breast Disease (WBD) is a novel muscle disorder in the poultry industry observed to frequently affect the breast muscles of high-yielding modern broilers. Characterized by extreme stiffening of the breast muscles upon palpation of the pectoral region, WBD is known to result in significant economic loss in the poultry industry, and may potentially cause behavioral alterations and reduced welfare in birds. To examine tissue changes associated with onset and pathogenesis of this disorder, a time-series experiment was conducted using chickens from a high-breast-muscle-yield, purebred commercial broiler line. Birds were raised for a period of six weeks, and breast muscles sampled on a weekly basis from selected birds and processed for light and transmission electron microscopy. Histologic presentation indicated presence of focal single-myofiber degeneration and hyalinization in the second week, preceding inflammatory reaction that started in the third week. Lesions in the fourth week were generally characterized by multifocal to diffuse muscle fiber degeneration and necrosis accompanied by increased inflammatory cell infiltration. Lesions in the fifth and sixth week were characterized by diffuse muscle fiber damage, fibrosis, fatty infiltration including granulomatous tissue encompassing lipid droplets, and irregular myofiber regeneration. Ultrastructural examination showed fibrosis with dense regular collagen fibers, irregular Z-discs, myofibril splitting, displacement and degeneration, including mitochondrial degeneration. This study therefore demonstrates that WBD exhibits an early onset in modern broilers and appears to assume a progressive course with acute inflammatory phase occurring in the earlier stages and chronic inflammation and fibrosis in the later stages of the disease course. 

Keywords: Broiler chickens, Wooden Breast Disease, transmission electron microscopy