Posture of calves can be influenced by nutrition and ambient temperature. Calf tail vein temperature (a proxy for body temperature) and standing time were extensively measured in 14 male calves (46 ± 1.5 kg initial BW) between 4 and 18 d of age. Thermocrons (Maxum Integrated Products Inc.) were taped to the tail vein to capture temperatures hourly. Accelerometers (Onset Computer Corp.) were attached to a plastic ankle bracelet and taped to the medial side of the right, rear leg to record posture every minute. Calves were fed free-choice dry feed and water and a 27% CP, 17% fat (DM) milk replacer fed at 2 rates (0.66, LOW, and 1.0 HIGH, kg DM daily) in 2 equal meals fed at 0600 and 1600 h. Calves were bedded with deep straw and maintained in an unheated, naturally ventilated, curtain-sided nursery with a well-drained rock floor. Ambient temperature averaged 2.5°C (daily averages ranged from −2.4 to 8.1°C). Data were analyzed as repeated measures in a randomized ANOVA to test MR rate and with linear regression analysis to test ambient temperature and time. Mean calf temperature was 38.4 ± 0.11°C and it changed diurnally with a 0.5°C daily range being highest at night (P < 0.05). Calf temperature was 0.1°C greater for calves fed a HIGH vs. LOW rate and it increased 0.02°C per 1°C ambient temperature (P < 0.05). Standing time averaged 299 ± 17 min/d and it increased 7.1 min daily with age and decreased 2.6 min daily per 1°C ambient temperature (P < 0.05). Standing bouts (a standing plus lying event) averaged 16.2 ± 0.5 daily and decreased 0.3 bouts daily per 1°C ambient temperature (P < 0.05). Bouts were 2.8 more daily for caves fed at the high vs. low rate and these extra bouts occurred during the AM and PM meals (P < 0.05). Standing time and bouts changed over the 24-h day and were greatest during the AM and PM meals, intermediate during the day between meals, and were the least overnight (P < 0.05). Feeding more milk replacer slightly increased body temperature and increased standing bouts during meals. A greater body temperature and less standing time overnight suggests that calves bedded with deep straw during cold temperatures conserved body heat by lying.