Simple Summary The transport conditions of end-of-lay hens to slaughterhouses are essential for their welfare. In this study, the effect of season, plumage colour, and transport distance on body weight loss, dead-on-arrival rates, and reject rates was examined. Transport-related data of 31.6 million end-of-lay hens over a two-year period from one slaughter plant in Turkey were analysed. Hens transported in the winter and spring seasons had a greater body weight loss and reject rates. Brown-feathered hens had a higher death rate, while white-feathered hens had a higher body weight loss and reject rate. Hens transported longer distances for slaughter had increased body weight loss, death rates, and reject rates. These results indicate that more care should be taken when transporting end-of-lay hens in cold weather and over longer transport distances. We suggest the transport should be reduced to a certain distance, and improved conditions ought to be provided to mitigate losses. Transport conditions of end-of-lay hens are important for their welfare. This study investigated the effects of season, plumage colour, and transportation distance on the welfare of end-of-lay hens. Retrospective data from 31,667,274 end-of-lay hens transported to a poultry slaughterhouse in Turkey were analysed. The mean body weight loss, dead-on-arrival (DOA) rate, and reject rate were 3.723%, 1.397%, and 0.616%, respectively. The effects of season, plumage colour, and transport distance on the evaluated parameters were all statistically significant (p < 0.001). The highest body weight loss was found in winter, while the lowest body weight loss was found in autumn. The average DOA rate was highest in spring and lowest in autumn. The highest average reject rate was found in spring (0.630%). Body weight loss, DOA rates, and reject rates were also significantly different among white and brown hens (p < 0.001; p < 0.001; p = 0.016, respectively). The highest body weight loss and reject rates were found in white plumage hens, while the highest DOA rate was found in brown plumage hens. The body weight loss and DOA rate were positively correlated with transportation distance (p < 0.001). The results of this study indicate that more preventive measures should be taken during the transport of end-of-lay hens, especially in cold seasons such as winter, and over longer transport distances, in regard to the welfare of these animals. Additionally, the transport of these animals should be lessened to a certain distance.