In central Brazil, there are two well-defined climatic periods, the rain and the dry season, the latter being marked by massive forage shortages in pastures. In this context, forage conservation such as making hay and silage for herbivores is imperative during the dry season. Grass hay is most commonly used for horses, but sorghum silage is often used for ruminants. The objective was to compare the nutrient digestibility, fecal production, and dry matter intake (DMI) of sorghum silage (Sorghum bicolor l. Moench CV. BRS 655) to that of vaquero hay (Cynodon CV. 90160 CD × CV. Mirage). Twelve Mangalarga Marchador fillies (8 months of age) were divided into two groups: S (sorghum silage, n = 6) and F (vaquero hay, n = 6). The ration was formulated to supply 3.0% body weight in dry matter (DM) per day, with a forage:concentrate ratio of 50:50 on a DM basis. The concentrate used was a corn-based ration formulated to meet or exceed requirements for growth when fed at 1.5% body weight DM to young horses. The animals were housed in individual stalls (3 × 3m) for a period of 25 days, with 21 days for adaptation, followed by 4 days of total collection of feces. During the collection period, an external marker of digestibility, Purified and Enriched Lignin (LIPE), was added to the concentrate as an external marker to determine the apparent digestibility coefficients of DM, crude protein, gross energy, neutral detergent fiber, acid detergent fiber, hemicelluloses, and cellulose. The forage DMI was calculated by subtracting the quantity supplied at each meal minus the amount of forage that was not eaten by the next meal (orts). The measures of digestibility of the sorghum silage were not different (P > .05) from that of vaquero hay. However, DMI of the sorghum silage was lower (P < .05) than the vaquero hay and may be of concern if fed for prolonged periods of time and not supplemented with carefully balanced concentrates. Purified and Enriched Lignin can be used as a marker for evaluation of digestibility of nutrients in weanling horses.