The ability to absorb changes and to anticipate future perturbations through adaptive capacity has been shown to be affected by early life experiences that can already be applied during the perinatal period. Adjusting the incubation temperature profile can program chickens during the embryonic phase to cope better with various challenges in later life, such as fluctuations in temperatures and/or pathogenic challenges. Especially slow-growing broiler chickens, that are often used in organic rearing systems with outdoor access, may benefit from this so-called embryonic thermal manipulation as they may experience more extreme temperatures and higher pathogen exposure than indoor reared animals. However, most studies about thermal programming have been performed in fast-growing broiler chickens. We have, therefore, investigated the effects of three different embryonic temperature profiles on chick quality and physiology at hatch of a breed of slow-growing broiler chickens that are often used in organic rearing systems with outdoor access. Slow-growing broiler chicken embryos (Hubbard, JA657) were exposed to one of 3 eggshell temperature profiles during embryonic day (E)8 until E16: (1) constant eggshell temperature (CON), (2) thermal manipulation (TM) with daily 12 h of a high eggshell temperature (HIGH), or (3) TM with daily 12 h of a high or low eggshell temperature (HIGH/LOW). TM was applied for 96 hours in total for the high and high/low EST treatment. Several chick quality characteristics per sex were measured at 6 h after emergence from the eggshell and blood was collected to assess the metabolic, antioxidant and inflammation status. Moreover, samples of the skin from the breast and upper thigh were collected to assess the (epi)dermis thickness and blood vessel perimeter. Samples of the jejunum and bursa of Fabricius were collected to assess villi characteristics. Results showed no effect of thermal manipulation on chick quality parameters such as yolk-free body mass, chick length, navel quality or relative organ weights in slower-growing broiler chickens (P≥0.10). Data of skin, jejunum, and bursa of Fabricius measurements are currently processed and will be presented during the conference. This study was part of the European PPILOW project that aims to improve the welfare of poultry and pigs reared in organic and low-input outdoor production systems. PPILOW has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N°816172.