<p>There remains a paucity of literature investigating the direct link between variability in dairy cattle core body temperature response to thermal indices, despite advances in precision livestock monitoring through sensor technology. Here we decomposed thermal indices and reticulorumen temperature data for 1,429 dairy cattle across three dairy farms in Victoria, Australia to investigate the variability in individual response to climate at different temperature humidity index (THI) thresholds. We revealed an overall positive association between THI and reticulorumen temperature deviation, with significant variability in sensitivity to thermal change among individuals. Increases in reticulorumen temperature were evident at a THI_max of 65, indicating a review of industry-established THI thresholds are required. Baseline THI levels were shown to be a major influencing factor for animal response. From these insights, our work is now focused on the development of a core body temperature derived phenotype for the selection of heat-tolerant animals.</p>