Researchers at the University of Delaware, in a project funded by the U.S. Poultry & Egg Assn. (USPOULTRY) and the USPOULTRY Foundation, reported a potential cause of woody breast lesions in broilers.

The modern broiler chicken, in the recent past, has been affected by a novel condition referred to as woody breast disease (WBD). The disorder, which largely targets the breast muscles of fast-growing and high-yielding birds, is characterized by extreme stiffening of the pectoralis major muscles, which causes a reduction in meat quality, according to the researchers.

With a prevalence rate of up to 10% in some flocks, the disease is leading to considerable losses in the poultry industry globally. While initial investigations of the disease focused more on chickens at market age (six to eight weeks old), relatively few studies were directed toward the onset and early pathogenesis of the disease in broiler chickens.

Dr. Benham Abasht and University of Delaware colleagues Drs. Carl Schmidt and Erin Brannick sought to characterize the early stages of WBD. Their study's main objective was to identify and characterize the onset, early course and prevalence of subclinical disease for this novel muscle disorder through genetic and histologic analyses.

The experimental broilers used in this study were raised from one day old to 49 days of age. Analyses revealed that heavier birds from one week of age to the end of the experiment were more predisposed to the development of WBD compared to birds of average size, Abasht et al. said.

Additionally, histologic investigations revealed an early onset of WBD, which started as localized vasculitis (inflammation of vessels) of veins in the breast muscle tissue by one week of age. Affected veins were surrounded by lipid and lipid-laden inflammatory cells, the researcher noted.

By two weeks of age, muscle degeneration was apparent, followed by muscle cell death and muscle tissue inflammation in week three. Beginning in week four and for the duration of the experiment, the affected muscle tissue went through a process of fibrosis, which resulted in the hardened muscle tissue seen in WBD, Abasht et al. noted.

In addition, genetic analysis revealed evidence of dysfunction in lipid metabolism and impaired metabolic pathways involved with cellular energy production.

Based on these results, the researchers said their study shows that the development of WBD is largely the result of damaged veins, characterized by inflammation of the veins and lipid deposition around the veins. This disruption of venous drainage and regional impairments of lipid metabolism precede the changes in the muscle tissue.

Until now, it remains unclear whether phlebitis (inflammation of the veins) is a cause or a consequence of the perivascular lipid accumulation and the inflammatory response, the researchers said.

This new understanding that inflammation of veins is the likely cause of WBD will provide an important direction for future research on this condition, Abasht et al. concluded.

The research project was part of USPOULTRY’s comprehensive research program encompassing all phases of poultry and egg production and processing.