Have seen it described that horses (and mules) performed as 'living machines'. Their power was used to pull wagons and artillery, carry supplies, as well as to transport soldiers. It's commonly estimated that 1.5 million horses and mules died (either from wounds or disease), out of about 3 million in use, during their wartime service. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.