Abstract: A batch of animal feed from a plurality of ingredients is prepared in a mixer/feeder wagon (1) where the ingredients require respective predefined mixing periods during a mixing cycle in the mixer/feeder wagon (1). The mixer/feeder wagon (1) comprises a mixing compartment (14) in which a mixing rotor provided by a paddle mixer (17) is rotatably mounted. Stationary chopping blades (42) mounted in a base (43) of the mixing compartment (14) cooperate with the paddle mixer (17) for chopping fibrous material during the mixing cycle. The appropriate predefined mixing periods required for the respective ingredients are determined in order to avoid over-mixing and under-mixing of the ingredients, and the predefined mixing period is defined as the number of revolutions of the paddle mixer (17) to which that ingredient is to be subjected.