I agree with the vet trip! Is there anything different in Oreo’s diet? It’s surprising how any small change can make a huge difference to them. Even a different kind of treat can upset their little systems.
I know that when BunBun has gotten a UTI (urinary tract infection) or his bladder sludge is bothering him, he gets weird about eating and drinks more water. He doesn’t stop eating the way they do during GI stasis or bouts of gas, but he is somehow less enthusiastic. Just picks at his greens rather than gobbling them down- sounds like Oreo is doing the same. Especially with the fact that she peed outside the litterbox, I would want the vet to rule out a UTI.
She might have a sore bum from poopy butt too- BunBun used to have messy poop a lot and his peeing habits would change- I think it might hurt them to pee so they do strange things like holding it for a long time or going outside their box, etc. Also, about the red mark on her hock- Bun had something like that when he got poopy butt! I wonder if their skin gets irritated very easily if they step in poo, or maybe they bite it off of their legs themselves and cause the red marks.
Good luck with Oreo at the vets- it’s probably something easily taken care of
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