Detachable front attachment unit (10, 40) for a self-propelled maize chopper, comprising: - a bottom part comprising a cutting device configured to cut down maize plants, and a feed device configured to evacuate the cut-down plants to a feed opening which, following mounting of the front attachment unit to the maize chopper, is configured to communicate with an inlet opening of the maize chopper, wherein the bottom part comprises fastening means for direct attachment to the maize chopper, and - a top part which is arranged above the bottom part, wherein the top part and the bottom part can be pivotably arranged with respect to each other, wherein the top part comprises a separating device configured to separate the maize ears from the stem, a conveying device and an outlet, wherein the conveying device is configured to convey the separated maize ears to the outlet, and wherein the separating device comprises gripping means to engage with the maize stem and separating means (133, 134) to separate the ears from the stem, characterised in that the top part is arranged with respect to the bottom part in such a manner that, during operation of the maize chopper, a maize stem first engages with the gripping means of the separating device, after which the stem is cut down by the cutting device of the bottom part, and in that the front attachment unit (10, 40) comprises an intermediate frame (15, 45), wherein the intermediate frame comprises first fastening means (153, 453) for attaching the bottom part to the intermediate frame (15, 45) and second fastening means (151, 152) for attaching the top part to the intermediate frame, wherein the bottom part is configured to be attached to the intermediate frame in a detachable way via the first fastening means (153, 453), so that the bottom part can be used for the maize chopper both separately, without the intermediate frame and top part, and integrated in the front attachment unit. - a bottom part comprising a cutting device configured to cut down maize plants, and a feed device configured to evacuate the cut-down plants to a feed opening which, following mounting of the front attachment unit to the maize chopper, is configured to communicate with an inlet opening of the maize chopper, wherein the bottom part comprises fastening means for direct attachment to the maize chopper, and - a top part which is arranged above the bottom part, wherein the top part and the bottom part can be pivotably arranged with respect to each other, wherein the top part comprises a separating device configured to separate the maize ears from the stem, a conveying device and an outlet, wherein the conveying device is configured to convey the separated maize ears to the outlet, and wherein the separating device comprises gripping means to engage with the maize stem and separating means (133, 134) to separate the ears from the stem, characterised in that the top part is arranged with respect to the bottom part in such a manner that, during operation of the maize chopper, a maize stem first engages with the gripping means of the separating device, after which the stem is cut down by the cutting device of the bottom part, and in that the front attachment unit (10, 40) comprises an intermediate frame (15, 45), wherein the intermediate frame comprises first fastening means (153, 453) for attaching the bottom part to the intermediate frame (15, 45) and second fastening means (151, 152) for attaching the top part to the intermediate frame, wherein the bottom part is configured to be attached to the intermediate frame in a detachable way via the first fastening means (153, 453), so that the bottom part can be used for the maize chopper both separately, without the intermediate frame and top part, and integrated in the front attachment unit.