One has to take into account that a significant part of those vehicles were "mobilized" civilian vehicles and captured foreign, of doubtful suitability.

http://www.lonesentry.com/articles/germanhorse/

"Despite highly ballyhooed emphasis on employment of mechanized forces and on rapid movement, the bulk of German combat divisions were horse drawn throughout World War II. Early in the war it was the common belief of the American public that the German Siegfrieds of Hitler's Blitz rode forth to battle on swift tanks and motor vehicles. But the notion of the mechanized might of the German Wehrmacht was largely a glamorized myth born in the fertile brains of newspapermen. Actually, the lowly horse played a most important part in enabling the German Army to move about Europe.

Public opinion to the contrary, so great was the dependence of the Nazi Blitzkrieg upon the horse that the numerical strength of German Army horses maintained during the entire war period averaged around 1,100,000. Of the 322 German Army and SS divisions extant in November 1943, only 52 were armored or motorized. Of the November 1944 total of 264 combat divisions, only 42 were armored or motorized. The great bulk of the German combat strength—the old-type infantry divisions—marched into battle on foot, with their weapons and supply trains propelled almost entirely by four-legged horsepower. The light and mountain divisions had an even greater proportion of animals, and the cavalry divisions were naturally mainly dependent on the horse.

The old-type German infantry division had approximately 5,300 horses, 1,100 horse-drawn vehicles, 950 motor vehicles, and 430 motorcycles. In 1943, due to the great difficulties in supply and upkeep of motor vehicles in the wide stretches of the Eastern Front, the allotment to divisions in that theater was reduced to approximately 400 motor vehicles and 400 motorcycles, and the number of horses was increased to some 6,300. The 1944-type divisions had about 4,600 horses, 1,400 horse-drawn vehicles, 600 motor vehicles, and 150 motorcycles. "

Mechanized Juggernaut or Military Anachronism?: Horses and the German Army of World War II (Contributions in Military Studies) by R. L. DiNardo

http://www.axishistory.com/index.php?id=6135

"... Without the extensive booty from the western campaign of 1940, these units would have remained without weapons and vehicles. Motor vehicles in particular played an important role in the motorization the divisions. The 18.PzD was equipped with strictly stock French motor vehicles until the end of May 1941...

Most of the motor vehicles (German, French or other booty trucks) massively used for various transports were not to have long lives under the rough conditions of the Eastern theatre of war. The progressive deterioration of the German army's motor vehicle situation already in the autumn of 1941 led to numerous use and new production of French trucks ... "

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