Heat stress is a major environmental constraint affecting livestock productivity, particularly in tropical regions. The present study evaluated antioxidant and endocrine responses to heat stress in Vechur and crossbred cattle to elucidate breed-specific adaptive mechanisms. Apparently healthy Vechur (n = 3) and crossbred (n = 3) heifers were subjected to thermoneutral (TN) and heat stress conditions in a climate-controlled chamber for 7 days each. The heat stress phase simulated tropical summer conditions (28-42 °C; 70-75% relative humidity). Blood samples were collected at the end of each phase to assess glutathione peroxidase (GPx), catalase, triiodothyronine (T3), thyroxine (T4), and cortisol. Heat stress significantly increased GPx activity in both groups (p < 0.001), indicating activation of antioxidant defense mechanisms, while catalase activity did not vary significantly. Although breed differences were not statistically significant, Vechur cattle exhibited a relatively higher GPx response, suggesting efficient antioxidant regulation under lower oxidative burden, where GPx predominantly functions. In contrast, catalase activity tended to be higher in crossbred cattle, indicating a comparatively greater oxidative load, as catalase is more active under conditions of elevated oxidative stress. Thyroid hormone levels (T3 and T4) declined in Vechur cattle during heat stress, reflecting adaptive modulation to reduce metabolic heat production, whereas crossbred cattle showed comparatively stable levels. Cortisol responses were inconsistent possibly due to the small number of observations, thus limiting its reliability as a standalone biomarker of heat stress in this experiment. Overall, Vechur cattle demonstrated a more efficient antioxidant and endocrine response, reflecting superior thermotolerance compared to crossbred cattle. These findings highlight the capacity of indigenous breeds in enhancing resilience and sustaining livestock productivity under heat stress conditions.