An engine system for an off-highway vehicle, comprising: a diesel engine configured to drive a driveline of the vehicle; an after-treatment arrangement configured to reduce emissions from the engine system; an after-treatment heating element configured to raise an operating temperature of the after-treatment arrangement; an electric energy storage device; and a controller configured to direct energy from the electric energy storage device to the after-treatment heating element in order to raise the operating temperature of the after-treatment arrangement.