Oxidative stress impairs the productivity and welfare of heat-stressed hair sheep; however, the key factors contributing to its occurrence remain unclear. Twenty-two Dorper x Katahdin ewe lambs weighing 23.5 +/- 2.8 kg and experiencing outdoor heat stress in a desert region were used to establish the contribution of climatic variables, physiological responses, metabolism, and feedlot performance to the oxidant-antioxidant imbalance. Pearson's correlation, principal component analysis, and multiple linear regression were applied to the datasets. Oxidative stress biomarkers showed positive relationships with average and minimum climatic variables, morning rectal temperature, serum triglycerides and insulin, and feed efficiency. Still, these biomarkers were negatively correlated with maximum ambient temperature (Te) and temperature-humidity index (THI), morning and afternoon respiratory rate (RR), total protein, and feed intake. While total oxidant capacity and fat oxidation were mainly associated with decreased maximum Te, protein oxidation was primarily associated with increased morning RR. Total antioxidant capacity was favored by a reduction in maximum THI and oxidative stress index (OSI) by an increase in maximum relative humidity. With minimal contribution (<= 6%), protein and fat oxidation were also explained by increased serum insulin and feed intake, respectively, whereas OSI was explained by increased weight gain. Overall, the presence of oxidative stress in feedlot hair sheep experiencing outdoor heat stress was regulated by a combination of climatic conditions, morning RR, and, to a lesser extent, productive performance.