Definitly let the vet do it. We had to have a horse euthanised and she went very peacefully. I had a kitten with an injury I had to shoot. It was a holiday weekend no vet available. It was awful, I had to shoot it several times to kill it. I can't imagine doing it to a horse. It was just awful, thats all I can say.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France