I'm not sure I have any useful advice for you, but I'll leave something my (extremely kind, caring) veterinarian said to me when I was having trouble making a similar decision about an aging cat:
"It's important to remember that these are animals, not people. They only live long enough for senescence to be an issue because we are taking care of them; in the wild, they wouldn't survive. And when we agree to be responsible for them, we also take responsibility for deciding when to let them go."
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Date: 2011-02-25 07:41 pm (UTC)"It's important to remember that these are animals, not people. They only live long enough for senescence to be an issue because we are taking care of them; in the wild, they wouldn't survive. And when we agree to be responsible for them, we also take responsibility for deciding when to let them go."