From Irregular Regular: Recollections of Conflict Across the Globe (The Extraordinary Life of Colonel David Smiley Book 3, Sapere Books, 2020), Kindle pp. 200-202:
One of the more unpleasant jobs I had to undertake at Ubon was to condemn and destroy the Japanese army horses. They had already marched over 1,500 miles from China and were in a terrible condition, both from starvation and ill-treatment. I had Tom Phillips to help me, who had been a racehorse trainer in Norfolk before the war, and out of 1,200 horses we inspected, we condemned 700 to be shot; they were dying at the rate of about ten a day from starvation and had only their droppings to eat. Some of the saddle sores were so big and deep that I could put my fist in them; I had never in my life seen such ill-treated horses.
Tom Phillips and I shot a great many, and I was often sick afterwards. The first day a deputation of Thais formed up and asked me not to kill the horses because it was against their Buddhist principles. I replied that it was a duty I very much regretted. I noticed plenty of Thais around afterwards removing their horses’ tails, before they were buried in huge pits dug by Japanese working parties.
Word reached me after the first day that the Japanese were saying that I had shot the horses for motives of revenge, because we had won the war. I therefore had them all paraded and through Sergeant Thomas told them that I was not shooting the horses because we had won the war, but to put them out of their misery after the ill-treatment to which they had been subjected.
I did not understand the Japanese mentality, for when leading their horses up to be shot, many of the men were in tears, and after they were shot they would take off their caps and bow at the graves, and even put flowers on them. A signal came from Bangkok suggesting that I was killing these animals unnecessarily, and that a veterinary officer would be coming to Ubon to inspect those that remained. A few days later a very fine-looking Indian colonel arrived and the Japanese paraded the remaining 500 that we had not shot for his inspection. He promptly condemned a further 400 to death.
Tom Phillips had left when I still had to shoot these 400 horses, and so I gave some of the Japanese vets back their pistols and told them to help me. After I discovered that they were taking up to three shots per horse, and found that some of the horses were being buried still alive, I stopped them and had to deal with the rest myself. Out of the 700 horses that I shot personally with an American .30 carbine with a folding butt which I used like a pistol, I had to give only one horse a second bullet. This was a horse that I shot in the correct place — at the centre of the X drawn from the ears to the eyes — but it trotted off apparently uninjured. When it was caught and brought back again, it was found to have a neat bullet hole in exactly the right place. It did not appear to be either frightened or in pain, or upset in any way. I fired the next shot downwards into its skull from above its ears and it dropped dead — I can only think it had a freak skull. I was very thankful when this distressing job was over.