Ruminant animals can convert fibrous plant material into nutritious food. Maize silage is an important animal feed and may constitute 50–75 % of the diet (Driehuis et al., 2008b) for a high-yielding dairy cows consuming up to 26 kg dry matter/day (Eastridge, 2006). This emphasizes the importance of utilizing accurate predictions of forage feeding value. Traditionally, the feeding value of diets has been determined from proximate analysis and tabulated digestibility coefficients determined in trials with animals. However, more easily conducted methods have been developed for routine determination of forage digestibility. Thus, the objective of this thesis is to compare in vitro and in situ methods in evaluation of maize silage fibre digestibility in dairy cows. Samples of maize silage will be subjected to in vitro incubations for 0, 2, 4, 8, 24 and 48 h and analysed on fibre content. In vitro method will be based on rumen inocula that will be obtained from dry ruminally cannulated cows. Concentrations of fibre will be also determined in the same samples after 0, 2, 4, 8, 12, 24 and 48 in situ incubation in the rumen of dry cows. Obtained results will be compared, statistically evaluated and expressed in tables and figures.