Image: By DonJay (Own work by the original uploader) [Public domain], via Wikimedia Commons
Eight million horses and countless mules and donkeys died in the first world war, used not only in cavalry but to transport ammunition's and supplies, many died not only from their injuries but also from exhaustion and disease caused by the appalling conditions they laboured under.
A farrier's axe was used to destroy badly wounded horses, all deceased horses had a hoof cut off as proof of their death. (Their regimental number was branded on the hoof.)
It's believed that 484,000 of the 1.2 million equines who served in the British Army during World War I perished and those that survived fared little better. Many were sold for meat whilst others were sold into a life of hard labour.
The plight of the survivors was brought to the attention of the British public in 1930 by Dorthy Brooke which resulted in the founding of an animal welfare charity dedicated to improving the lives of working equines world wide ~ The Brooke