In my opinion it is not the total amount of protein in a food but rather the quality of the protein (the bioavailibility — how much is used by the body and how much becomes waste (aka blood urea nitrogen)). Speaking as the owner of a dog born with kidney disease I know that high quality protein creates less nitrogen for her kidneys to have to filter (and thus less in the urine). And my dog with kidney disease actually eats a HIGH protein raw diet — ranging from 45 to 54% protein. In fact, I have 8 dogs all eating high quality kibble with raw and high protein canned toppers or exclusively high protein raw. I don’t have brown spots on my lawn — 8 dogs-high protein-no brown spots.
Additionally, they know that senior dogs actually need as much as 50% more protein than adult dogs as they are not as efficient at digesting their food.
I know you don’t want supplements but a trick used by those with dogs with kidney disease (and confirmed by science to work) is feeding probiotics and foods for those probiotics called prebiotics. This causes a “nitrogen trap” and routes some of the nitrogen in the blood through the colon instead of the kidneys. Gets pooped out instead of peed out.
