Forage conservation in the hay form is commonly used in the feeding of equines, but due to technical difficulties for conservation and availability for the market, forages with different conservation conditions (silage and pre-dried silage) have been provided as alternatives. However, few studies still cover the effects of the different forms of roughage conservation in equine nutrition. This study aimed to evaluate variations in dry matter intake by mares fed with different forms of roughage conservation of the oat plant. In a 3-way Crossover Design, 6 healthy mares, mixed breed, aged between 3 and 13 years, were individually confined in 24m2 bays, with ad libitum water supply. The mares received 3 different treatments: oat hay, conventional oat silage, and pre-dried oat silage. The treatment adaptation period was 18 d, followed by 5 d of data collection. The roughages have been provided ad libitum. For dry matter intake evaluation the quantities of roughage provided, leftovers, and waste for each animal were measured. The animals were dewormed, and a dental examination was also performed before the beginning of the experiment. The collected data were submitted to ANOVA statistical analysis and the Pearson correlation coefficients were calculated. A GLM procedure was performed to compare the diets used. Significant variation was observedbetween treatments (P = 0.0015), in which pre-dried silage and hay showed higher consumption (9.15 kg/DM/day and 9.08 kg/DM/day respectively) compared with conventional silage (7.9 kg/DM/day). The low dry matter (DM) density of conventional silage (25% DM) for about hay (87% DM) and pre-dried silage (46% DM) may have caused greater filling of the gastrointestinal tract of the animal, causing faster satiety and contributed for the consumption variation. Another point to be highlighted is the concentration of organic acids and pH in the silages, in which the conventional silage had a higher acetic acid content (25621.4 mg/kg/DM) which had the lowest pH (4.2), while the pre-dried silage had the lowest pH acid (456.5 mg/kg/DM) and higher pH (5.1), suggesting that conventional silage, more acid, led to its lower consumption, since according to the literature, horses prefer sweeter foods. In the hay, there is an absence of organic acids due to its way of conservation by dehydration. Oat hay and pre-dried oat silage have better dry matter intake compared with conventional oat silage for mares under the evaluated conditions.