Hi Lisa,
So sorry to hear about your lab: ( Increased BUN from diet is tied into protein but it sounds like your dog isn’t eating a lot of protein. Rawhide is a source of protein, but he is off those now. Any other high protein chews you give him consistently? Rawhide contributes calories too so hope the weight loss is from eliminating those from the diet vs something else.
Another source of protein that your vet probably already considered is from bleeding into the gut. This may or may not show up on a regular blood count. A rectic count in addition to the normal blood counts could be done to make sure that constant regeneration isn’t going on.
If this still could be kidney problems from a diet perspective controlled phosphorus levels are recommended in kidney disease. Phosphorus parallels protein which is likely where the rec to avoid high protein comes from.
Sounds like more diagnostics will be needed to sort this out.
