PS9-1. Early Growth and Wooden Breast Pathology.

Abstract Wooden Breast (WB) myopathy originates early in development, yet its relationship with growth during initial stages remains poorly defined. We aim to evaluate how body weight and breast muscle weight are associated with early histopathological lesion severity (day 14-17 post-hatch). In addition, we assessed sex-specific differences in the incidence and severity of early WB. Chicks were raised in five hatches. In total, 526 Pectoralis (p.) major samples were first subjected to hematoxylin and eosin (H&E) staining and evaluated by histopathological analysis for the severity levels of myofiber degeneration and myositis. To determine what variables had a significant effect on histologic features, ordinal logistic fit models were run separately for myositis and degeneration. In this model, hatch, age, sex, and p. major muscle weight (PM weight) were used as predictors. Another model was used for both histologic features with the same predictors, substituting PM weight for body weight. The ordinal logistic fit models were significant for myositis (p < .0001), and degeneration (p < .05). The fit models for myositis suggested that sex effect (p < .02) and hatch effect (p < .0001) were significant. In the model that considered PM weight as an effect, PM weight was significant (p < .0001). In the model that considered body weight as an effect, body weight was significant (p = .0048). Age was not a significant effect in either model. The fit model for degeneration including body weight as an effect suggested that hatch effect (p = .0234) and body weight (p = .0073) were significant. Hatch and body weight were not significant in the model that considered PM weight. Sex effect and age were not significant in either model. These results demonstrate that early WB-lesions are linked to increased growth at early stages of post-hatch development. These observed associations with body weight and PM weight support the hypothesis that rapid growth contribute to early pathogenesis of WB.