Re-evaluating corticosterone as a welfare biomarker in broilers using UPLC/MS-MS: Limited responsiveness to heat stress, disease challenges, and environmental enrichment.

Corticosterone (CORT) is widely used as a physiological indicator of stress in poultry welfare research; however, its responsiveness across biological matrices under endogenous challenge conditions remains debated. The present study investigated whether experimentally induced changes in welfare status are reflected in CORT concentrations measured in plasma, dorsal feathers, and droppings using a validated UPLC-MS/MS method. Two experimental trials were conducted to induce variation in broiler welfare status. In the first experiment, male Ross 308 broilers were exposed to thermoneutral or cyclic heat-stress conditions during the finisher phase, with or without access to multifunctional cooling platforms as environmental enrichment. In the second experiment, Ross 308 broilers were challenged with two infectious disease models: coccidiosis (Eimeria spp.) and respiratory disease (infectious bronchitis virus combined with avian pathogenic Escherichia coli). At 41 days of age, plasma, dorsal feathers, and droppings were collected and analyzed for CORT. Across both experiments, plasma CORT was consistently detectable but remained at low concentrations and did not differ between control and challenged groups. Feather CORT was below the limit of quantification in all samples, and around 30% of dropping samples were below the limit of detection. These results suggest that, under the conditions tested, endogenous CORT measured by UPLC-MS/MS in plasma, feathers, and droppings shows limited responsiveness to common welfare challenges and enrichment strategy, raising questions about its sensitivity as a welfare biomarker in broilers.