When my cat Florence was getting in years and couldnt deal as easily with the litter box as she might, my vet recommended something whose name I forget, but it came in a tube. You put a bit of it on your finger, and the cat licks it off -- apparently, to them, it's pretty tasty, and it works as a digestive. I'll dig around in the old vet records and see if I can find what it was. It might help.

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