[fixermark]

It's really a case-by-case basis thing.

I grew up with a mutt that I loved dearly. My parents got her because my Dad had read something or other in (I think) Popular Science about how the "dog of the future" would be a mutt, and the mutting of genes would suppress bad recessive traits. Then she got sick as a puppy, had an allergic reaction to her medication, and suffered permanent brain damage. That having been said, she was a perfect house pet; lived to be a very ripe old age and was good natured, just a little slow to respond to things.

If you're a breeder and there's something wrong in the genetics of the dog you're breeding, stop breeding that dog. But resolving genetic issues isn't as simple as just throwing mutts together; you really just roll the dice on a new set of strengths and weaknesses when you do that.

[rjsw]

A mutt could still be the offspring of two pure bred dogs and have inherited genetic problems from both.

[Jtsummers]

Exactly. Mutts may often be better than their purebred parents (by various objective and subjective criteria), but in the end it'll take a few generations of mutts and, well, survival of the fittest before you can see a general trend towards improvements in health and longevity.

Genetics are a lottery, starting with unhealthy parents the odds are against the offspring. It'll take generations for the population as a whole to move towards being healthier on average.