Abstract This study examined pathomorphological changes and meat quality alterations associated with Wooden Breast Myopathy (WB) in total of 192 broiler chickens divided into Ross 308 (n=96) and Cobb 500 (n=96) heavy hybrids at ages 42, 60, and 70 days. WB occurrence remained consistently high (>73%) across periods, peaking on day 70 (83% for Ross, 90% for Cobb). Cobb broilers had better production results and carcass traits parameters after day 42 and day 60 of the experiment (p≤0.05). Genotype did not affect WB occurrence or severity, while slaughter age influenced severe cases WB occurrence, increasing from 11.67% on day 42 to 36.67% on day 70 (p=0.003). The presence of WB was associated with higher ultimate pH, lightness (L*), redness (a*), and yellowness (b*) of the muscle (p<0.0001), except on day 70. Physicochemical and color parameters were also influenced by slaughter age (p<0.0001). On day 42, drip loss (p<0.0001), cooking loss (p≤0.05) and shear force (p<0.0001) were affected by genotype. On days 60 and 70, the differences in water retention capacity were observed only between normal and severely affected breasts (p<0.0001). For each slaughter age severely affected WB had higher shear force compared to normal breasts (p<0.0001). Additionally, with the increasing slaughter age of broilers, drip loss, cooking loss, and shear force of the breast meat were increased (p<0.0001). The results obtained regarding the occurrence and severity of WB and its consequent meat quality alterations suggest that extended fattening is not recommended for poultry production.