I had a dog with kidney failure, but hers was due to the effects of long-term diabetes and Cushings Disease. The dog I have now had BUN levels in the high end of the normal range since the time I adopted her (she was a little less than a year old). I get her blood work done twice a year. Everyone thinks I'm weird to do that, but I wish I had known ahead of time with the health issues of my other dog. Anyhow, when Haley's BUN level finally went above the normal range, I got a little panicky. The vet tried to blame it on her food (frozen raw, grain-free dry, and veggies). I read a lot of info with my last dog, and recent research shows that a low protein diet doesn't help. I still feed Haley the raw food (no grains) and add veggies (to help fill her up) and cottage cheese.
There are a few supplements I started giving her, and her blood work that was done 6 months after the one that showed her above the normal range showed that her BUN level was even below the middle of the normal range -- lower than it was when I first got her. I give her 4 supplements for it. I have no idea which one, or it it is all of them, help her, but I will just continue to use all 4 of them. I'm not sure how it would be trying to give them to a cat, though. Luckily they didn't bother Haley at all.
1. The first is just a probiotic. I had found some information on a supplement made specificly for animals with kidney failure, and it was just probiotics at a high price. I give her 1/2 a capsule of a probiotic for humans.
2. An immune strengthener. Some people that reviewed this product mentioned that it helped their pets with kidney problems. It is for both dogs and cats.
3. Vetri-Science Renal Essentials. Haley isn't thrilled with hers because it is liver flavored, and she doesn't seem to like any liver-type treat. It looks like the cat version is fish flavored. I used to buy it from Only Natural Pet (same as above supplement), but I recently found it MUCH cheaper: