I've had to put down a few dogs/couple of cats as seniors. I just 'knew', don't know how I knew but I knew.
My latest one was a month ago, my 13 yr old aussie, healthy as a horse, stopped eating, diagnosis, mass/enlarged heart. I got him eating, his breathing was getting worse and worse, he stopped eating, I knew I had to let him go
It kills me that he walked right into that clinic with his butt wiggling and a smile on his face, as sick as he was
Now I have my 5yr old gsd, in great shape, and my 14 yr old aussie
I thought I was going to have to do it again a couple weeks ago, (urinary issue), she's fine now, she is still active, eating like a pig, tho obviously has arthritis and some doggie alzheimers. This is the first time since 1991 I've had only two dogs
I always have questioned whether I was putting any of my animals down to soon, what if I gave them one more day or a week? As time passes, I know I did it when I should have done it, tho I'd give anything for that extra day or week