From Catastrophe 1914: Europe Goes to War, by Max Hastings (Knopf, 2013), Kindle Loc. 10368-10389:
The British took 53,000 horses to France in 1914, and other armies used them in like proportion. The official historians noted: ‘The enormous wastage from animal casualties of a modern war was under-estimated.’ The BEF’s horses and mules suffered an annual mortality rate of 29 per cent, with over 13,000 dead in France and Flanders before New Year 1915 from disease or enemy action. Alexander Johnston reckoned that on the march to the Aisne he passed a dead horse every two hundred yards: ‘poor brutes, they have a terrible time of it’. Many such casualties – shot, crippled or ridden to exhaustion – were drawn from the 165,000 hunters and plough horses purchased for the British Army in the first twelve days of war. In September the retreating Germans threw down spiked metal caltrops, or ‘crows’ feet’, to cripple pursuing cavalry. These frequently achieved their purpose, especially when compounded by French housewives’ practice of tossing stove ashes onto rural tracks without removing nails and other old iron.
Many horses fell victim to incompetent or brutal handling. Vets catalogued examples of mistreatment by ignorant riders and grooms: artillery drivers ‘chucking’ horses in the mouth [yanking back on the reins]; cavalry wantonly neglecting to feed or water their mounts; men galloping horses on paved roads without urgent need; riders ignoring saddlesores. Cavalry remount depots were formed at Ormskirk, Swaythling and Shirehampton, and beside each was a veterinary hospital capable of tending a thousand four-legged patients. Army stables at Pitt Corner camp near Winchester at one time held more than 3,000 sick and injured animals.
Meanwhile heavy plough horses, conscripted against expert advice, proved quite unsuitable for the artillery role for which they were earmarked. The official historians noted: ‘Veterinary officers … foresaw their weakness for military purposes, and anticipated the heavy loss which would ensue if they were indiscriminately employed in war … because of great susceptibility to disease, large food and watering requirements, and inability to stand forced marches.’ Heavy horses perished in thousands in France, partly because of the extreme vulnerability of their feet to wet weather. Both the French and the British made huge foreign purchases of replacements, but the right sort of animal was identified only after harsh experience. Many Canadian remounts died on the Atlantic passage, or soon after arriving in Britain. It was found that the most suitable stock were tough American country beasts from areas like the Dakotas, rather than barn-reared horses. By the war’s end, the British Army’s animal strength rose to 450,000; an estimated total of two million hapless horses and mules served on both sides of the Western Front. The Royal Army Veterinary Corps, which mustered just 360 personnel in 1914, numbered 28,000 four years later.