Not necessarily, I've known several working coonhounds that lived well into their teens with most still able to put one up from time to time. Just slower than in the past.

I tend to think it's the extremes that shorten a dogs life. Extreme size or form on either end or extreme breeding of to closely related or to small of a gene pool over extremely long periods. Extreme focus on one trait to the exclusion of all others.

I can feel your pain! I have had to put a couple down and that is why I don't have one now. I am lost without one yet don't want to deal with the heartbreak.

I took my Springer mix to the vet 2 years ago to get a teeth cleaning as his breath smelled like rotted meat for quite a while. The vet found a squamous cell carcinoma growing just under his eye which had already ate a good bit of his bone away around his teeth. The vet said based on the how aggressive it was, the dog probably didn't have but a few months until it ate up to his brain. He also did a biopsy and sent it to the lab. He said there were some treatments including radiation and chemo but I decided I would chose quality of life rather than prolong a poor quality life.

The tumor got to be around golf ball size and smelled awful. He survived the year and I took him in for a annual visit last summer and the vet was amazed. He wanted to do a little blood work and if all checked out, he said he could debulk it. The vet cut out a good portion of it but it was all through the bone and he couldn't get it all.

The smell and tumor is still growing and its noticeable again after about 15 months but it hasn't slowed him down even though he is now 12 years old.

As I look back through the years, I think he had this most of his life as every once in a while on long trips, his breath would smell the same as it does now. I suspect it was growing slow and finally became evident after about 10 years.