The most humane way to put a horse down is by using a veterinarian-administered lethal injection. This method ensures that the horse passes quickly and painlessly. The veterinarian will first sedate the horse to make it calm and relaxed, and then administer a second injection that will stop the heart.
Other methods of euthanasia, such as captive bolt stunning or gunshot, can be used in emergency situations where a veterinarian is not available. However, these methods are not as quick and painless as lethal injection and should only be used as a last resort.
It is important to remember that euthanasia is a difficult decision, and there is no easy way to go through it. However, by choosing a humane method, you can help ensure that your horse's passing is as peaceful and painless as possible.