Four mares were used in experiments to determine in vivo dry matter (DM) digestibility of corn silage and to evaluate the new in vitro system, DAISY incubator, to determine nutrient compound of corn silage. Horses were fed thrice daily at the amount 20 kg corn silage per day. All the diets, refusals and faecal samples were collected. Samples were analyzed for contents of DM, crude protein (CP), crude fiber (CF), organic matter (OM), crude fat, neutral detergent fiber (NDF) and acido detergent fiber (ADF). Further, faecal samples were taken from each horse to form inoculum. Forty nylon bags (0.25g corn silage) were placed in each vessel, and in vitro fermentation was carried out for 48 h to determine DM, CP, CF, OM, crude fat, NDF a ADF. Partial resultsfrom Exp. I indicated that nutrients composition of corn silage corresponding with previous determination of other authors.