
Depending on the blood values, tripe is useful as it is very low in phosphorous, so consequently I used to use small pieces of dried tripestick as a treat (cut with secateurs

) I would be wary of the majority of standard treats and avoid anything too high infat. A great source of protein also negligible in phosphorous are cooked egg whites, cooked rice too is good. I would have thought it better to put on to a KD diet, designed for dogs with poorly functioning kidneys rather than a senior diet.
Had a dog with chronic kidney failure who I kept healthy and happy for 8 months on a home cooked diet, after she was given 2 weeks, even the vets were amazed.
All the best
Kat