The aim of the study was to investigate the effects of dietary enzymes and training on carbohydrate digestibility, blood morphology and biochemistry in horses. A group of 10 animals was divided into two treatments: control (C) and supplemented with enzymes (ES). For 14 days, group C was fed a diet based on 6 kg of hay and 6 kg of whole grains of oat, while the ES group was fed the same diet with the addition of xylanase/cellulase. After 14 days of the experimental period and 5 days of the washout process, the treatments were reversed for another 14 days. During the whole experiment, horses were trained 6 days a week including walk, trot and gallop. Blood and faeces sample were analysed. Blood parameters were measured before and after training. Sieve analysis of ES horse faeces showed fewer large particles in comparison to C animals. Neutral detergent fibre digestibility was higher in ES horses. Starch digestibility was also elevated in ES animals. Enzyme supplementation did not affect blood parameters or most of the biochemical blood indices, although reductions in blood cholesterol and urea concentrations were noted in ES horses. Leptin concentration was increased and obestatin level was decreased in ES horses. Training increased the number of erythrocytes and leukocytes, haematocrit value and haemoglobin concentration. In addition, it influenced the factors responsible for anabolic/catabolic pathways and turnover of carbohydrates, lipids and proteins, including a decrease in blood insulin level. The study showed that dietary supplementation with fibrolytic enzymes improves feed digestibility and energy balance in horses, and has no visible side effects during exercise.