Roy, R. C., Cockram, M. S. and Dohoo, I. R. 2015. Welfare of horses transported to slaughter in Canada: Assessment of welfare and journey risk factors affecting welfare. Can. J. Anim. Sci. 95: 509-522. There is concern over the welfare of horses transported from the USA for slaughter in Canada. This study provides information on welfare issues associated with the transport of 3940 horses from 150 loads to a slaughter plant in Canada. Multivariable regression analyses were used to examine the association between journey characteristics and welfare outcomes. Injuries are considered in an accompanying paper. Five percent of the horses arrived from within Canada (median journey duration=12 h), and 95% arrived from five states in the USA (median journey durations 15-36 h). Seven percent of horses from Canada and 1% of horses from the USA arrived with pre-existing conditions. Five percent of the horses had a body condition score <3 (scale 1-5) and <1% were lame. Six horses from the USA (0.16%) arrived in a non-ambulatory condition. A linear mixed model showed that plasma total protein concentration increased with journey duration (P<0.001). No pre-transport measurements were possible and lairage and slaughter may have affected some of the results. Fewer severe welfare problems were identified than in similar studies conducted previously in the USA. However, multivariable analyses suggested that long journeys were associated with an increased risk of dehydration.