Yeah the deuce and a halfs and Jeeps. Anyone who knows anything about tactics knows that supply is what battles are won and lost on. The Russians thanks to us had a lot of very good trucks and were able to move things around better than the Germans could. At the time American built trucks were the best in the world (still are IMHO), they held up to the Russian roads better than others.
http://www.o5m6.de/studebaker_us6_u2.html
These helped turn the tide more than people in this country realize.
Problem with horses is they all died and became food in December and Jan of 1941/42, so they were replaced by men or vehicles, sometimes replacement horses which were either Russian captured or farm horses. Also pre war German calvary officers would raise and train horses and then sell them to the government for a profit. When the war started German officers were riding into battle on their own mounts, which were quickly nationalized along with all other German horses to shield them from the monetary loss of losing one, and so the government could insure a supply.