The aim of this study was to evaluate the apparent digestibility of a total mixed ration (TMR) versus a traditional mixed hay/cereals diet. Four adult trained Standardbred geldings – BW = 478±37 kg - were used. The two diets consisted of 20 kg of a commercial TMR - corn silage, alfalfa hay, wet brewers’ grain, oat, apple pomace, molasses cane, soybean oil and mineral/vitamin supplement - (Diet 1) or 7 kg of meadow hay and 4.5 kg of cereal-mix - corn, oat, barley and protein/mineral/vitamin supplement - (Diet 2). The trial was conducted according to a Latin Square design (2x2). After an adaptation period of four weeks, total faeces and urine were collected for 6 days. Both feed and faeces samples were analysed for DM, OM, CP, EE, CF, NDF, ADF, cellulose, hemicellulose, ADL and GE. Data were analysed by ANOVA. The apparent digestibility and nitrogen balance of the two diets were compared. DM, OM, CP and GE apparent digestibility were significantly different between the diets, with higher values for unifeed diet than traditional diet. Energy requirement was satisfied by both diets (96.54 vs 95.55 MJ). Nitrogen balance showed negative values in both diets (- 61.67 vs - 9.05), but the hay/cereals supplemented diet showed the best protein utilisation.