Burlinguette, N. A., Strawford, M. L., Watts, J. M., Classen, H. L., Shand, P. J. and Crowe, T. G. 2012. Broiler trailer thermal conditions during cold climate transport. Can. J. Anim. Sci. 92: 109-122. Thermal environments within broiler transport vehicles are dependent on ambient conditions and, if poorly managed, can be a welfare concern. To effectively manage broiler transport, the environmental conditions throughout vehicles must be understood. Under standard commercial practices, temperature and humidity levels in double-trailer broiler vehicles were examined for a range of ambient temperatures (-24 to 11°C). During warmer ambient conditions (9.8°C) trailer roof vents and side curtains were all open, which resulted in a narrowing of the on-board temperature range (10.3 to 16.7°C). As ambient temperature cooled side curtains and some of the roof vents were closed. This resulted in increasingly variable and more extreme thermal conditions, with heat and moisture accumulated along the midline of the load near the front of the lead trailer and near the back of the rear trailer. At an ambient temperature of -22.1°C trailer temperatures ranged from -20.7 to 21.7°C with an estimated 58.6% of the load volume being exposed to temperatures below 0°C. In addition, the trailer humidity ratio rose 14.0 g kg^-1 above ambient and conditions approached saturation (RH>80%) in 55.2% of the load volume. These results support the need to find a means to remove moisture and redistribute heat on broiler trailers during cold ambient conditions.