Influence of Wooden Breast myopathy on sarcomere length and tensile strength in commercial chicken breast

Wooden Breast is a myopathy seen on chicken breast muscles in the last years, causing economic losses. It is associated with hardness and paleness of the muscle, necrosis, fibrosis and macrophage infiltration. The aim of this study was to investigate the differences in sarcomere length and tensile strength between normal and Wooden Breast in chicken. For the sarcomere length measurements 20 unaffected chicken breasts and 21 Wooden Breasts were used. For half of each group electrical stimulation was applied. Sarcomere length was measured in four different locations of each breast: cranial and medial area, surface and depth. The tensile test experiment involved three experimental groups, with 20 samples for each group: unaffected, with focal lesion and with diffuse lesion. Samples were cut from the surface layer of cranial and medial area of every chicken breast, both on longitudinal and transversal direction of the muscle fibers. Results showed that Wooden Breast syndrome has a significant effect on sarcomere length, leading to increased lengths in the affected muscles compared with the normal muscles (p<0.05). There was less lengthening of the sarcomere as result of electrical stimulation in WB muscles compared with normal chicken breasts (p<0.05). The difference in sarcomere length between WB and Normal was smaller in the surface layer of the muscle in comparison with the depth layer. There were no significant difference between the mean values of tensile strength in Normal samples and Focal WB samples, but significantly higher values in Diffuse WB samples (p<0.0001). The Diffuse samples yielded significant higher tensile strength when they were stretched parallel with muscle fiber direction, compared with cross-sectional direction of stretching (p