Calf housing is naturally thermodynamic with interactions between various elements such as wind speed, air temperature and humidity. This study investigated the effect of the proportion of time that calves were exposed to effective environmental temperatures below their lower critical temperature (LCT) on their daily liveweight gain (DLWG) within the first month of life. This study used the naturally occurring climatic environment whereas other such studies have been conducted under climatically controlled conditions. Air temperature (oC), relative hu-midity (%) and wind speed (m/s) were recorded within the calf housing from day of birth until approximately 28 days of age with calves health scored and weighed at regular intervals. Calves were housed from birth until 6-14 days old in individual hutches then moved into group housing Igloo pens. Whist individually housed, calves that spent less than 0.32 of their time below their LCT had a DLWG of 0.06±0.34kg/d (mean± se) compared to calves that spent more than 0.97 of their time below their LCT that had a DLWG of -0.19±0.045kg/d. When group housed, calves that spent less than 0.01 of their time below their LCT hada DLWG of 0.59 ±0.18 kg/d whereas calves that spent more than 0.28 of their time below their LCT had a DLWG of 0.53±0.23kg/d. The proportion of time that calves were exposed to effective environmental temperatures below their LCT had a significant effect on DLWG when calves were individually housed. Therefore, exposure to effective environmental temperatures below the LCT can be detrimental to the growth of the calf in the early stages of life.