Not trying to argue, but do you think that the studies on the specifically targeted down pasterns in German Shepherds? I mean, it is not that common that every dog whose protein is out of line gets the condition. I have stayed within a range that long-time breeders have used, and I have avoided the condition in my dogs. But whether the lines do not have the genetic component of that going on, or if I have successfully avoided it is unknown.
Still, sometimes it is better to go with what experienced breeders have found over veterinarians, because the breeders' focus is on one dog breed, where veterinarians are seeing 200+ dog breeds and mixes and cats and birds and reptiles, etc. Their knowledge base is wide, but in a lot of cases more shallow because of how wide it must be. Since this condition only shows up in some dogs, studies might not have captured it. It does seem that changes in protein in affected dogs has improved the situation.
Also, pano seems to be improved when feeding more appropriate levels of protein and fat. Sometimes.
I think that a strong dog food company, like Fromm might have a better handle on this than veterinarians because they have a dog in the fight, and have feedback that might really help them. Most dog food companies I wouldn't trust either to be thorough about data/feedback.
I would agree that in general, a breeder is going to have a better understanding of specific ailments within a breed.
They have more connections, see more dogs, and dedicate their lives to understanding what they and others produce. It's far more specialized. Not all research we see will take into account whether the dogs are from health-tested parents, look at the pedigrees (we know there are dogs out there that have produced horrible ailments), or look at diet or exercise, just as a few examples.
Until there's a study on the breed, done throughout P1/P2 - F1/2/3 etc... it's hard to say in regards to joint development. There's so many specific genes involved, some that interact during development and then become in conflict with one another later in life. We know that a diet too high in protein is related to arthritic problems, but too high is different for each individual. Protein quality, source of protein (animal vs. plant), etc. all play a role. An appropriate and quality diet doesn't ensure longevity, but it can help it if the genetics are there.
Unfortunately we can't always trust that a dog food company will have a dog's best interest in mind, though obviously a lot of vets don't either. If you have had the chance to look into Taurine Deficient Cardiomyopathy, Fromm is a so-called culprit. So are other high quality brands. They are aware of these issues, and no changes have been made at the moment. It may change as money is what talks. While the understanding so far is that it is only a correlation, we do also know that with dietary changes there have been improvements and in many cases, regression of the disease if it is not in late stages. There are some foods with zero known incidence as of this moment, and some with high incidence of the disease.
I got that part covered, don't worry. If you look up overthinking in the new puppy ownership dictionary you'll find my picture.
I think my main problem is my educational background is in the hard sciences. I am used to theories being tested and either validated or not. When I see people take a single study involving a handful of dogs and then making sweeping, definitive conclusions I can't help but think "That isn't science!" I know that's the most rigorous a field like nutrition can get but it still bothers me.
In general while I am always trying to learn more I've told myself not to overthink or panic. You want to do your best based on what you know. But if I use a diet with 28% protein and my puppy gets an issue I can't think, "OMG what did I do? I should have been at 26%!" The "science" of it is just not that exact.
I also have a background in the hard sciences, and I agree that it makes it very difficult to feel comfortable or confident in what to do because there is a lot of research - some good, some bad. But as you know, where the information comes from and how it came about is far more important than what that information might be.
When you're looking at feeding your dog, at the end of the day you simply feed the dog in front of you. Your dog may never tolerate high protein levels, or if your dog is like mine, might do poorly on kibble formulations that are low protein (within the 23-25% range). The food you might want to feed might result in a sensitivity or intolerance, and now you're back at square one trying to find a food you approve of and feel comfortable feeding. The diet you might want for your dog based on your research may never work for your dog. So sometimes you have to take the scientific, logical thinking aspect out of some of it and simply look at what your dog does well on. Keep certain guidelines in mind for the well being of your dog, especially during growth and development, but really there are no absolutes when it comes to nutrition. There are dogs that live on scraps and live longer and look healthier than a dog fed on the highest quality kibble money can buy.