What is Elvis' Calcium level? and Urine Specific Gravity?
Personally
with those creatinine and phos numbers I would be doing sub q fluids & talking to the vet about starting an aluminum hydroxide phosphorus binder.
My 17 yr old girl's cre number when last tested in mar was 223 & her BUN 17 she's scheduled for retesting early Aug & I am going to talk to her homeopath vet about starting sub q's as an early boost to her system, right now she feels great & acts like a healthy 5yr old.
Great that the BUN dropped
the venison could very well have boosted the Cre #, certain meats like rabbit are high in phos so that should be limited.
For the 1.5 yr olds red gums it is possible it was the plant, many are toxic some are just irritating to cats. I would keep a close eye on his mouth just in case.
Was his urine tested for crystals or cultured for bacteria?