The goal of this project is to evaluate the role of hatching egg incubation conditions in a costly meat quality defect that manifests in the fastest-growing, highest-yielding birds currently plaguing the commercial poultry industry called "Wooden or Woody Breast" (WB). This degenerative myopathy is characterized by extensive connective tissue accumulation (fibrosis) within breast muscle resulting in meat that is hard to the touch, has reduced consumer acceptability, and has low value due to poor product functionality, which ultimately costs the US broiler industry hundreds of millions of dollars annually. Our preliminary data show that the muscle satellite/stem cell (MSC) populations, which are essential for muscle growth, are altered in WB-affected birds. To date, post-hatch WB interventions have been largely unsuccessful. The relationship between hatchery conditions and MSC function in high-yielding broilers as related to WB myopathy has been largely unexplored. Previous research aimed at exploring the impact of thermal manipulation during late-stage incubation and the early post-hatch indicates that muscle stem cells and subsequent hypertrophic muscle growth can be compromised in broilers when temperatures are not optimal. Therefore, it is critical to explore what pre-hatch conditions may be affecting skeletal muscle development such that fast-growing, high-yielding chicks are predisposed to developing WB myopathy post-hatch. The project objectives are to assess the impact of 1) early- and 2) late-stage incubation temperature conditions on broiler chicken skeletal muscle developmental characteristics such as myofiber number, post-hatch MSC activity, growth performance, and carcass parts yield, and the incidence and severity of the WB meat quality defect in chicken breast fillets. The completion of this work will not only push us toward eliminating this costly meat quality defect from the global chicken meat supply but simultaneously increase our knowledge of how egg incubation conditions fundamental skeletal muscle growth mechanisms which will further enhance our ability to produce enough high quality, nutritious chicken meat products to meet growing consumer demand.