Here's another expert opinion:
"The dog can digest large amounts of proteins, especially those of animal origin" stated Prof. Dominique Grandjean DVM, Ph.D., at the Fourth Annual International Sled Dog Veterinary Medical Association Symposium (page 53 of 1997 PROCEEDINGS).
Current, and even ignored thirty-year-old research by Dr. David S. Kronfeld and others, spells out the evolutionary need for canines to have sources of high quality protein such as is found in animal tissues. Meat (muscle tissue), organ tissues such as liver, kidneys, spleen, and heart are particularly rich in the complex molecules called amino acids that end up as protein.
There are 22 amino acids involved with the dog’s metabolism and of these the dog requires 10 different amino acids to be supplied by the diet. The other 12 required amino acids can be manufactured internally in the dog’s liver. Grains tend to be better sources of carbohydrate, a quick source of energy. Animal-derived tissues are more easily digestible and have a more complete array of amino acids than do grains.
Meats and meat by-products (meat by-products are blood and organ tissues and do not include hide, hair, hooves and teeth) are exceptionally high quality protein sources for dogs. (That’s right! Meat by-products are excellent sources of nourishment for dogs. By-products do not contain floor sweepings, old flea collars, gasoline or machine parts. We all need to have an open mind and take a look at what by-products really are.)
"But too much protein is bad, right?" you ask. Do your own research and poll half a dozen nutrition specialists (not the guy who runs the local pet shop) and here is what you will find: There is no general agreement among expert nutritionists regarding what constitutes “too much” protein in the dog’s diet. Research shows that dogs have a high capacity for digesting and utilizing diets containing more than thirty percent protein on a dry weight basis. (Dry weight basis means the food with no moisture present. Dry dog food in a bag usually has 10 percent moisture and canned food has about 74 percent moisture.) If left to catch and consume prey to survive, as wild canines do every day, dogs’ diets would be even higher in protein than what is generally available commercially.
Think about it ... do you ever see a stray dog grazing in a corn or bean field to allay its hunger? Nature has created a meat-eating machine in the dog and every day in practice I see the health benefits displayed by the feeding of meat-based diets.
Dogs fed poor quality diets look and feel great only if their caretakers also feed table scraps such as chicken, meat, eggs, cottage cheese and other “left-overs.” Meat such as chicken, poultry, beef or fish should be the first ingredient listed in any dog food you judge to be "the best".
"But what about the older pet?" you might ask. "I’ve always been told that high protein diets are bad for an older dog's kidneys; even my veterinarian says so." What researchers have proven is this: In dogs that actually have kidney damage or dysfunction (regardless of their age) and that have a BUN level greater than 75, restricted protein intake may be beneficial but not because of any adverse impact on the kidneys. The protein these impaired dogs ingest should be of high quality such as is derived from eggs, poultry, and meat. On the other hand, high protein levels in a food DO NOT cause kidney damage in the normal, healthy dog or cat!
So what does that mean for the older dog? It means that you should not restrict feeding high quality protein to older dogs just because they are older. There is even some valid research that indicates older dogs may need a higher percentage of protein in their diets than they required during middle age. This shouldn’t be a surprise to us because dogs evolved through the ages as meat eaters. The grain-based diets for dogs did not even exist until seventy years ago when we humans demanded the convenience, simplicity and economy of dog food in a bag.
The bottom line is this, and it is based on fact -- protein intake does not cause kidney damage in healthy dogs or cats of any age. So whatever you choose as “the best” diet for your dog, make certain that an animal tissue source is listed first in the ingredient list.
Your older dog or cat should, if its kidney function is normal, receive the benefits of a high quality diet rich in animal-derived protein. For an excellent source of easily understood nutrition principles consider purchasing Canine and Feline Nutrition, by Case, Carey and Hirakawa.