<p>Research on the repeatability, plasticity and predictability of the body temperature of endotherms is limited. Following developments in precision livestock farming, dairy calves have emerged as a model organism to explore these questions in a large endotherm. This study aimed to harness long-term, high-frequency recordings from reticulorumen temperature boluses recordings to investigate the repeatability, plasticity and predictability of reticulorumen temperature before, during and after weaning in 98 dairy calves. Using both frequentist and Bayesian mixed modelling, we found that reticulorumen temperature was moderately repeatable (<i>R</i> = 0.258), that reticulorumen temperature was plastic over the three weaning stages but that plasticity varied on an individual level, and that individual calves differed in the predictability of their reticulorumen temperature (CV_P = 0.242). We also showed that weaning had a complex impact on reticulorumen temperature, its repeatability, and its predictability, with individual calves responding to weaning differently. This study is the first to formally quantify inter- and intra-individual variation in reticulorumen temperature in calves, adding to a restricted body of work on variation in body temperature in endotherms. We suggest accounting for inter- and intra-individual variation in methods aiming to automatically detect disease in calves using reticulorumen temperature would increase their accuracy.</p>