This may be the hardest decision you will face. If you know that your pet has a terminal illness, and that it's only a matter of time, then your ability to end its suffering will be both a blessing and a great weight. Faced with such a profound responsibility, how do you know when it's time to act? The surest guideline is to follow your pet.
Sometimes a pet will let you know very clearly that the time has come. She will withdraw. You will notice that she no longer enjoys being around anyone. You'll find her in unusual places, far removed from activity. She may even display a quality that looks like sadness. In this case you can almost feel her misery, and it's obviously time to act.
But other times a terminal illness is more of a gradual decline, with the pet experiencing good days alternating with bad. If you want to keep enjoying her so long as she's enjoying her own life, you will have to become something of a judge, watching and weighing. The thing you'll be asked to evaluate is her quality of life.
How good are her best days? Does she seem to enjoy the company of her family? Is she out of pain? Do her good days outnumber the bad? These are difficult questions because they're subjective, but if you watch your pet you'll get the answers.
We made this website in memory of Bosco, so we will describe how we went through this process with him. First of all, he never withdrew; he was alert and happy every day. Even when the pain medication was no longer providing complete relief, he still ate voraciously and wagged his tail to see us and was genuinely involved in our family's life. We'd expected him to withdraw, but eventually we saw that it wasn't going to happen. He made it very clear that he was enjoying his life, even though he couldn't get up and it hurt to walk.
That forced us into the evaluation mode -- we were going to have to decide when his life had lost too much quality for it to be humane to have him go on. So long as he could get up by himself, it was easy. As the cancer progressed, though, he'd have days when he couldn't. Then he'd get better somehow, and be able to stand up and walk by himself. Finally he was no longer able to get up at all, but if we hoisted him onto his feet he could walk. Some days he would take a little walk down the street, or go into the sun for a nap. Other days, though, it'd be all he could do to stumble into the yard to urinate. It was during this time that we understood our vet's words about evaluating good days versus bad. She'd told us that when the bad outweighed the good, then it was time.
It was finally time when two days passed with him unable to walk. We had been changing sheets and towels underneath him many times a day, keeping him clean, but he suddenly developed bedsores. There was nothing we could do. Even though he was as forceful and involved as ever, enjoying the family and wanting attention just as he always had, we could not let him go on. In fact, his eyes were bright and he was still himself when his vet came to our home on that last afternoon.