The month, average air temperature, relative humidity, number of pigs of each sex per trailer load, journey time, type of trailer and bedding, and waiting time at the processing plant were recorded from 16,323 trailers transporting 2,730,754 pigs to a packing plant in the USA during a year, together with the numbers of pigs that were dead on arrival, injured or unable to walk. The percentage of pigs dead on arrival increased at temperatures above 20 degrees C, and the percentage of pigs unable to walk increased at temperatures of 5 degrees C or below. The journey time and waiting time at the processing plant influenced the percentages of dead and injured pigs and pigs unable to walk.