Wooden Breast Disease in Commercial Broiler Chickens: A Histologic and RNA-Seq Study

Wooden Breast Disease (WBD) is a myopathy of fast-growing commercial broiler chickens, the most obvious symptom being palpably hard breast muscle (pectoralis major) tissue. The affected breast muscle is both visually and texturally unappealing to consumers, causing economic loss to the poultry industry. Recent research on WBD has focused on understanding the molecular contributors of breast muscle damage, fibrosis, and lipid infiltration resulting from WBD. The current study was conducted to compare gene expression and histology of the liver between WBD-affected and unaffected chickens. Live birds, from a purebred line of commercial broiler chickens, were clinically examined by manual palpation of breast muscle at 47 days of age. Liver tissue samples from 4 affected and 4 unaffected birds were used in high throughput mRNA sequencing (RNA-seq) using Illumina 2500 HiSeq platform. After aligning sequence reads to the chicken reference genome (Galgal4) using TopHat, differential gene expression analysis was performed using Cuffdiff. A total of 113 genes were differentially expressed (DE): 71 of these genes were upregulated and 42 were downregulated in affected birds. The DE genes were used for functional annotation clustering with DAVID Bioinformatics Resources. The most prominent biological pathways enriched with the DE genes included transmembrane, metabolic, extracellular matrix receptor interaction, and oxidoreductase. Our results indicate that metabolism of bile and cholesterol is disrupted and liver damage and regeneration is occurring more often in affected birds. Histological examination of affected livers presented inflammatory cell infiltration as nodules surrounding veins. In conclusion, this study shows that, in addition to breast muscle, the liver is affected by WBD, indicating further physiological complexities involved in the occurrence of this muscle abnormality in commercial chickens.