Please answer a question about the following article about Franco-Prussian War:

Despite odds of four to one, the III Corps launched a risky attack. The French were routed and the III Corps captured Vionville, blocking any further escape attempts to the west. Once blocked from retreat, the French in the fortress of Metz had no choice but to engage in a fight that would see the last major cavalry engagement in Western Europe. The battle soon erupted, and III Corps was shattered by incessant cavalry charges, losing over half its soldiers. The German Official History recorded 15,780 casualties and French casualties of 13,761 men.

With battle at Metz, what factor shattered the efforts of III Corps?
incessant cavalry charges