German Army had massive logistical problems from the very beginning of the war. In spite of taking rail cars and locomotives from all over Western Europe and reorganizing Polish railways to help the Wehrmacht, and taking cars and trucks from all over Western Europe, the army relied mainly on trains and horses.
The German military relied mainly on rail transport to move supplies long distances. While the mighty German Wehrmacht appeared unstoppable during its invasion of Poland, the “destruction of railways by both sides was so heavy that the logistic system was saved from collapse only by the speedy Polish surrender.”
(Source: Supplying War: Logistics from Wallenstein to Patton by Martin van Creveld)
The Wehrmacht relied on horses to pull its artillery and supply wagons, even ambulances.