Diet Ratios

Question
Should the percentage of each required element of a dog's diet (carbs, fat, protein, etc.)change with the unique genetics of a canine breed (Shepherd vs Yorkie) or would a change be indicated for the activity level (Working vs Idle foot rest) or age, and if your answer is yes, this ratio changes, where may I find a reliable and trustworthy source for the correct ratio for a specific dog? Thank you for your time and assistance.

Answer
It really doesn't need to.  Most dog foods are formulated to have more than enough protein and fat for most dogs.  The balance is then carbohydrates.  Even if a dog needs a little more of this or that, it is there.  Dogs use what they need of the protein and fat, and burn the remainder as energy.  

The protein levels vary partly because there are 2 ways to provide enough of each individual amino acid.  You can put in less protein, but carefully select ones to give the right balance of amino acids.  Or you can put in more protein from less well balanced sources and still have all the dog needs of everything.  Excess protein does make a little more work for the kidneys, but still less than in nature where the diet is high in meat.  

Working dogs and other highly active dogs do require more protein and energy.  There are working dog formulations that may be better for highly active dogs.  As dog age, their activity level declines.  If you reduce their calories to maintain good body condition, you may short them on vitamins and minerals.  Thus the lower calorie senior formulations.  

As for a ''reliable and trustworthy'' source, it would be tough to find one for whether the sun came up or not today.  So much of what you read is influenced by marketing hype.  I am convinced many websites that sound like a non profit group actually are funded by dog food companies.  It is a way for the smaller companies to market without buying expensive ads.  Also, many foods are distributed by small, part time reps.  Some of them aren't above filling dog forums with marketing hype.  There is actually somebody here that gives her website in her answers where you can buy what she recommends.  She gives far different answers than I do.  For a while there was another that gave as her qualifications that she owned a holistic dog food store.  

I don't know if there is any science behind Royal Canine's and others' breed specific foods or not.  Even if somebody did a massive study showing Labs had slightly different requirements from Lhasa Apsos, would a small show Lab be the same as a huge, fine boned field Lab?  With so much of what you read being speculation, and no references to it, I doubt any such studies have been done.  Science is based on testing, not theories.  

It is like Aristotle and Galileo. Aristotle though about it, and declared heavier objects fall faster then light ones. For most of the next 2000 years, educated people knew that. Then at the dawn of modern science, Galileo lugged the large and small balls up the the tower of Pisa, and dropped them off. They hadn't read Aristotle, and both hit the ground at the same time. I am afraid the dog world is full of thinkers. Most of my answers are based on my own results trying what I have been taught by the best there is.

One last point.  There is good data, even if funded by a dog food company, showing how you feed is very important to a dog's health.  I trust the information at http://www.longliveyourdog.com/twoplus/RateYourDog.aspx because it is the way the dog guide school was teaching before the net was filled with misinformation.