I put down my beloved mare a year ago. She was 8. She had cutaneous lymphoma, of a form the vets rarely see. But despite that, she was overall entirely fine. We did lots of various treatments - everything short of chemo. We showed, and won.
One day, I noticed that her left hindquarter was losing muscle tone.
Within a week, she looked skeletal on that left hindquarter. She was never openly lame. Ran around with her friends, kicked all the geldings asses.
I didn’t know what was wrong, but in my head I knew that whatever it was was the final straw for her. She had lived a hard knock life, 47 races (sometimes weekly for a month or two), and then came to me to be a trail/show horse. She had done her time, she had struggled with daily needles and prednisolone, foot issues, etc. I promised her right at the cancer diagnosis that I was not going to allow her to go down in flames, I was going to send her out like the badass that she was.
And I did. Fat (with the exception of that one hindquarter), glossy, mane pulled, and tail looking its best. I put wild pheasant feathers in her hair and send her over the bridge. They stopped the biggest heart in the world that day.
I don’t regret it, not for a minute. She had been through so much, and no matter what the outcome of the atrophied pelvis was, she didn’t deserve to suffer for a bit more.
Hugs to you, OP. This is never easy. Our job is to take their pain, their suffering, their unhappiness, and bring it onto ourselves as our burden to bear.