Reasons for performing study: In endurance horses, commonly fed 80% forage, energy is provided mainly by VFA produced in the hindgut during cell wall degradation, but cell wall digestibility has been reported to be impaired by exercise.
Objectives: To assess the influence of a long-term endurance conditioning on cell wall digestion in horses.
Methods: The total tract apparent digestibility of dry matter, organic matter and fibrous constituents, solid and liquid total mean retention time and the faecal microbial ecosystem of purebred Arabian horses were measured for 2 years in 2 longitudinal experiments.
Measurements: Performed at the beginning of each year for control level and after conditioning periods corresponding to incremental endurance racing levels: 60, 90 (year 1) and 120 (year 2) km. During the 5 measurement periods, feed intake and diet composition were similar.
Results: In year 1, digestibility of DM, OM and NDF was higher after 10 weeks of training (P = 0.008, P = 0.010 and P = 0.031, respectively), corresponding to the 90 km level, compared to the pretraining level. In year 2, NDFd and (NDF–ADF)d tended to be higher (P = 0.06 and P = 0.07, respectively) after the 17 weeks conditioning necessary to reach 120 km level, than before training. These variations were not systematically associated to a longer total MRT, neither to an increase in the microbial fibrolytic activity.
Conclusions: Digestibility of DM, OM and NDF appeared to be higher after endurance conditioning. Such an increase could be beneficial for endurance horses as it would provide more energy from forage degradation. Additional experiments are needed to elucidate the mechanisms, understand some contradictory results and investigate methodological aspects.