In horses, physical activity has been reported to have an impact on digestion that, in some cases, may result in a decrease in total tract apparent digestibility of fiber.1,2 Such an impact could be particularly detrimental for endurance horses, which are submitted to severe nutritional challenges, such as the supply of energy throughout the entire race; and for which the provision of volatile fatty acids originating from fiber degradation probably plays a crucial role. The objective of the present study was to investigate the effects of a long-term endurance conditioning on total tract apparent digestibility of fiber in horses.