The objective of this study was to evaluate the physiological mechanisms and health resilience of Duroc pigs reared in an outdoor system compared to a conventional indoor system. A total of 24 Duroc pigs (approximately 3 months of age) were randomly assigned to either an indoor (IN, n = 12) or an outdoor (OUT, n = 12) rearing system for a 45-day trial. Growth performance (body weight and ADG) and spleen organ index were not significantly different between the two rearing systems (p > 0.05). Hematological profiles, including leukocyte and erythrocyte indices, showed no significant differences (p > 0.05), although plateletcrit tended to decrease in the OUT group (p = 0.08). For serum biochemical parameters, pigs in the OUT group exhibited significantly higher concentrations of total protein, triglycerides, calcium, and sodium compared to those in the IN group (p < 0.05). Additionally, serum albumin and glucose levels tended to be higher in the OUT group (p < 0.01). No significant differences were observed in liver and muscle enzyme activities (AST, ALP, GGT, CK) between the treatments (p > 0.05). In conclusion, outdoor rearing did not compromise growth performance or induce chronic physiological stress or tissue damage in Duroc pigs. Instead, it promoted active energy and lipid mobilization, enhanced protein metabolism, and improved mineral homeostasis, demonstrating the robust physiological adaptability of the Duroc breed to outdoor environments.