This study aimed at evaluating, in previously inactive Standardbreds horses, the effect of 5 weeks of an exercise training programme on nutrient digestibility and faecal fermentative parameters (FFPs). As an increase in digestibility had previously been reported in trained endurance horses, we hypothesized that similar results would be found in horses being trained for other types of exercise on a different type of diet. After 3 weeks of dietary adaptation, a digestibility trial (DT1) was undertaken, over 3 days, in eight untrained Standardbreds with a fresh faecal sample being collected on the second day for FFP determinations. Six of the eight horses undertook a training programme, and after 5 weeks of exercise, the DT and the FFP measurements were then repeated (DT2). DT2 began after 3 days of inactivity. The same natural meadow hay (H) and pelleted complementary feed (CF) were fed throughout. For 5 days before the DTs, horses were fed 2.1% BW on a dry matter basis (55:45 ratio H:CF). Body weight and body condition score remained constant. Apparent digestibility of dry matter, organic matter, neutral detergent fibre, hemicellulose, crude protein and gross energy, as well as faecal total volatile fatty acids (VFA), acetate and propionate concentrations were significantly (p < 0.05) higher at DT2 than at DT1. A 5-week exercise programme had a positive impact on nutrient digestibility and FFP. Training may improve dietary energy supply, in particular via increased hindgut VFA production. The potential improvement of digestive efficiency with training should be taken into account when formulating nutritional recommendations for the exercising horse, particularly when performing light work, which is low-intensity exercise for 1-3 h per week.