Stress in Free-Roaming and Shelter-Housed Dogs: A Review of Neurobiological, Physiological and Behavioral Mechanisms Relevant to Welfare Assessment

Stress is a major influencing behavior, health, and welfare in free-roaming dogs, particularly in environments characterized by unpredictability, social instability, and frequent human interactions. Although research on canine stress responses has expanded considerably, current knowledge remains fragmented across the neurobiological, physiological, and behavioral domains, limiting the development of comprehensive welfare assessment strategies. Importantly, free-roaming and shelter-housed dogs should not be viewed as entirely separate populations, since many shelter dogs originate from free-roaming environments and share similar stress-related experiences. This narrative review provides a comprehensive synthesis of current evidence on stress mechanisms in free-roaming and shelter-housed dogs The literature was explored across major scientific databases, and a total of 69 relevant studies were included. Particular emphasis was placed on the activation and regulation of the hypothalamic–pituitary–adrenal (HPA) axis, associated neuroendocrine alterations, and their behavioral expression. The strengths and limitations of commonly used physiological indicators, including cortisol measured in blood, saliva, feces and hair, were critically examined in relation to their applicability in real-world contexts. Behavioral manifestations of stress, such as fear- and anxiety-related responses, aggression, withdrawal, and stereotypic behaviors, were analyzed as functional outcomes of neurobiological activation and environmental challenges. Environmental stressors typical of shelter conditions as well as the role of human–dog interactions in stress modulation are also discussed. By combining neurobiological, physiological, and behavioral perspectives, this review highlights the importance of multidimensional stress assessment and proposes a conceptual framework linking biological mechanisms with observable behavioral indicators of welfare across the continuum from free-roaming to shelter environments. These findings may support the development of evidence-based welfare assessment and management strategies for free-roaming and shelter-housed dog populations.