Feed efficiency is essential in pork production optimizing growth and maximizing nutrient use. This project will validate the use of thermal efficiency index (TEI) for evaluating feed efficiency in growing pigs. This study investigated the relationship between thermal efficiency and stress resilience. In a 2 x 2 design, weaner pigs were assessed for TEI, with high and low TEI animals selected; half of each group received a commercial supplement in water (DSS, designed to reduce stress) for 24h before and after stressful events, and half were treated as control. Pigs were challenged with a controlled handling and mixing stressor at 12 and 16 weeks respectively. Infrared temperature was evaluated before and after each stressor with additional salivary cortisol and thermal imaging measurements in the second replicate. TEI shows a consistent correlation with average daily gain, which indicates a valid metric for measuring pigs’ growth. Use of DSS in water significantly reduced lesion scores at mixing compared to the control and produced a greater change in TEI in response to handling and mixing stressors.