This observational study investigated market pig deaths during transport from the farms to the abattoirs in Ontario. Three trucking companies were studied with respect to temperature, relative humidity, and global positioning data for 104 trips that delivered 21 834 pigs from 371 producers to Ontario abattoirs. 94% of producers investigated  in this study experienced no in-transit pig losses but the overall average in-transit loss was 0.12%. As trailer  temperature increased, pig losses increased. This study was conducted in the summer months of  July to October 2004 to gain valuable knowledge on the effect of transport temperatures on animal welfare and health. It was concluded that temperature and humidity monitors were less  expensive than pig losses during transport and that sprinklers or fans in transport trailers would be efficient at reducing in-transit market pig losses.