The objective was to study the kinetics of transit and degradation of the fiber from guinea grass and the waste from soybean pre-cleaning (WSPC), ensiled with different proportions of mass (0, 100, 150, and 200 g WSPC/kg total mass). Four crossbred (Gyr × Holstein), fistulated cattle with an average body mass of 400±50 kg were organized in a 4 × 4 Latin square experimental design. The fiber utilized in the study of the transit kinetics was stained with chromium mordant, whereas the in situ technique was adopted for the degradation kinetics. The level of inclusion of WSPC only affected the true digestibility and the mean retention time. The addition of waste from soybean pre-cleaning to the silage of guinea grass is beneficial, in terms of kinetics of digestion and passage, at up to levels close to 100 g/kg, because after this quantity the fiber digestion and passage in and through the reticulo-rumen are impaired and there may be alterations in the ruminal environment that will affect the use of silage by animals.