Effect of white striping myopathy on breast muscle (Pectoralis major) protein turnover and gene expression in broilers

A study was conducted to evaluate the effect of white striping (WS) of broiler breast muscle (Pectoralis major) on protein turnover and gene expression of genes related to protein degradation and fatty acid synthesis. A total of 560 day-old male broiler chicks Cobb 500 were allocated in a total of 16 pens, 35 chicks per pen. A completely randomized design was conducted with a 2 x 3 factorial arrangement (2 scores: severe and normal, and 3 breast meat samples sites). At d 60, 20 birds were randomly selected, euthanized, and scored for white striping. Scoring was either normal (NORM, no WS) or severe (SEV). Also, the same day, 17 birds (16 infused, one control) were randomly selected and infused with a solution of 15 N Phen 40% (APE). Breast muscle tissue was taken for gene expression analysis of the following genes: MuRF1, atrogin-1, IGF-1, insulin receptor (IR), fatty acid synthetase, and acetyl CoA carboxylase (ACC). Each bird was humanely euthanized after 10 minutes of infusion and scored for WS (NORM or SEV). Samples of the breast muscle (Pectoralis major) were taken at different layers (3 samples per bird: ventral, medial, dorsal), along with a sample of excreta for 3-methylhistidine analysis. Out of the 16 breast samples taken, only 10 were selected for analysis based on the WS score (5 NORM and 5 SEV). No significant differences (P > 0.05) were found in fractional synthesis rate (FSR) between SEV WS, NORM and sample sites for breast meat. However, fractional breakdown rate (FBR) was significantly higher in birds with SEV WS compared to NORM (8.2 and 4.28, respectively, P < 0.0001). Birds with SEV WS showed significantly higher (P < 0.05) relative expression of MuRF1 and slightly higher (P = 0.07) relative expression of atrogin-1 than the NORM birds. These birds also showed lower (P < 0.05) relative expression of IGF-1 than NORM birds. Further studies are needed to better understand why birds with severe white striping are degrading more muscular protein and mobilizing more fat.