Interesting Cross Breed on Craigslist

I see a number of older pits (fourteen, fifteen) that end up in shelters in one way and another. Overall a pretty long lived breed.

Go Dogs wrote:
the longevity of 22 year old Chihuahuas with the primal, sturdiness of a Tibetan Mastiff

Why is it dogs do not follow the mammalian relationship between lifespan and body size?

Body size, energy metabolism and lifespan

Bigger animals live longer.

That kid's test is a novel and great idea but it has not been proven effective.

Here's a novel idea; pet buyers who want healthy dogs should stop buying breeds with breed defining physical features (mutations) that predispose them to health issues. Any breed that looks significantly different than "village dogs" was developed by selecting for abnormal/unusual features (mutations).

For Heaven's sake. A little O/T, on CBS This Morning- a 16 year old kid came up with an inexpensive, accurate test to detect early-stage pancreatic cancer. He did it because he couldn't understand why no one else had! The current tests cost $800 and only detect it in later stages.
So, you seem to be throwing up roadblocks rather than looking for answers. If a goal would be to combine the longevity of 22 year old Chihuahuas with the primal, sturdiness of a Tibetan Mastiff-start from the beginning!
If there is a breed of dog that throws unpredictable genetic mutations-maybe don't use them so much trying, to develop the 'Methuselah' dog.

How would you test for health without putting stress on the body? For example, if a dog is never fed food that it is allergic to how would you know the dog has allergies before you bred it? Or are you proposing to test for everything possible and only breed those dogs that are not carriers or affected in any test?

What if there is no test for the disease?

For example in Border Collies there is a recently identified genetic mutation that causes deafness between 3-5 years of age. We know the chromosomal region where the mutation is but not the exact site of the mutation. Carriers do not go deaf. How would you propose to select against this disease before we get a test; stop breeding all dogs from lines that have produced deaf dogs? How far back in those lines do we go, 2 generations, 5, 10; what do you do with the offspring from the previous generations?

Cancer in Greyhounds is another good example. Lets say a male Greyhound dies of cancer. Does that mean all of its offspring and subsequent generations should no longer be bred? What about the other offspring of the sire or dam that produced the Greyhound with Cancer?

What if no test is possible for a genetically linked disease because there are too many genes involved? For example epilepsy.

What happens to the diversity in the gene pool when entire lines and offshoots are removed? The COI goes way up and more genetic mutations are seen because carriers get bred to carriers.

I'm not comparing breed to breed, function to function. All that I am wishfully suggesting is that there would be a dog developed specifically to be a healthy, companion dog. IOW: Breed for that and forget the appearance, size, and performance. Just another option for people.
I don't think one would have to wait for the dam to be 10+ years old before producing a litter-look at the ancestors, and make a prediction. Longevity, while important, would be of a lesser concern than general health.

In order to selectively breed for "longevity" one would only breed those dogs that live a long time. That would mean mothers would be 10+ years of age when they have their first litter.

BCSnob wrote:
I'm not talking about what the breed was developed to be, but the breeding goals of that litter. Dogs bred to be pets (regardless of the breed) were not bred for performance.

I thought that was what you meant, but wanted to clarify.

Go Dogs wrote:
I have seen very, elderly lap dogs. I have seen many dogs bred for sports, that were riddled with joint and bone problems.
A happy medium would be nice.

I've seen lots of complaints about dogs bred solely to be pets with significant health issues and dogs bred for work that live to 13+ years of age. None of these examples (yours or mine) are evidence for or against my premise; they are just hearsay. Real data would include the incidence rates of diseases in dogs bred for work vs bred for pets (I'm not talking about breeds developed for work vs pets but the breeding goals of the litters).

I'm not talking about what the breed was developed to be, but the breeding goals of that litter. Dogs bred to be pets (regardless of the breed) were not bred for performance.

Greyhounds are an interesting case; they have concentrated genes which predispose them to some cancers (which is not evident until after breeding age) and until tests can be found for these genes it cannot be bred out. No one can selectively breed out a disease that does not strike until after the age a dog can be bred (we're not going to breed 10 year old dogs for the first time). Greyhounds seem to have two populations in terms of life expectancy; those that don't get cancer (12+) and those that do get cancer. Greyhounds have one of the lowest incidences of hip dysplasia which would impact performance and therefore is selected out.