A vehicle system including a vehicle, the vehicle comprising: - an internal combustion engine provided with an output shaft; - a power take-off for the attachment of implements to the vehicle; - at least a pair of wheels; - first power transmission means configured to allow power transmission between said output shaft and said wheels; and - second power transmission means configured to allow power transmission between said output shaft and said power take-off; the vehicle system further including an electric power pack, which comprises: - a motor-generator; and - energy storage means configured to store energy generated by said motor-generator and supply the energy stored to said motor-generator; and - a motor-generator control unit configured to be connected to a vehicle control unit in a releasable manner and to cooperate therewith to control said motor-generator, wherein said motor-generator is configured to be coupled to said power take-off in a releasable manner, such that a mechanical output power provided by said motor-generator is transmitted to said output shaft through said second power transmission means and thus to said wheels through said first power transmission means, wherein said electric power pack further comprises a motor-generator control unit configured to be connected to said vehicle control unit in a releasable manner and to cooperate therewith to control said motor-generator, and wherein said vehicle control unit is configured to control said motor-generator by generating control signals for controlling said motor-generator; said motor-generator control unit being configured to: - receive said control signals from said vehicle control unit; and - operating said motor-generator based on said control signals, and the vehicle system is characterized in that said vehicle control unit is configured to inhibit fuel supply to said internal combustion engine while controlling said motor-generator to provide mechanical output power. - an internal combustion engine provided with an output shaft; - a power take-off for the attachment of implements to the vehicle; - at least a pair of wheels; - first power transmission means configured to allow power transmission between said output shaft and said wheels; and - second power transmission means configured to allow power transmission between said output shaft and said power take-off; the vehicle system further including an electric power pack, which comprises: - a motor-generator; and - energy storage means configured to store energy generated by said motor-generator and supply the energy stored to said motor-generator; and - a motor-generator control unit configured to be connected to a vehicle control unit in a releasable manner and to cooperate therewith to control said motor-generator, - a motor-generator; and - energy storage means configured to store energy generated by said motor-generator and supply the energy stored to said motor-generator; and - a motor-generator control unit configured to be connected to a vehicle control unit in a releasable manner and to cooperate therewith to control said motor-generator, wherein said motor-generator is configured to be coupled to said power take-off in a releasable manner, such that a mechanical output power provided by said motor-generator is transmitted to said output shaft through said second power transmission means and thus to said wheels through said first power transmission means, wherein said electric power pack further comprises a motor-generator control unit configured to be connected to said vehicle control unit in a releasable manner and to cooperate therewith to control said motor-generator, and wherein said vehicle control unit is configured to control said motor-generator by generating control signals for controlling said motor-generator; said motor-generator control unit being configured to: - receive said control signals from said vehicle control unit; and - operating said motor-generator based on said control signals, and the vehicle system is characterized in that said vehicle control unit is configured to inhibit fuel supply to said internal combustion engine while controlling said motor-generator to provide mechanical output power. - receive said control signals from said vehicle control unit; and - operating said motor-generator based on said control signals, and the vehicle system is characterized in that said vehicle control unit is configured to inhibit fuel supply to said internal combustion engine while controlling said motor-generator to provide mechanical output power.