Hmmmm, maybe her arthritis is starting to make her feel like sleeping in her box instead? Do you think she could be older than 3?
Many buns sometimes do this, it’s not uncommon and usually not a cause for concern unless it’s paired with other symptoms. Also many buns don’t eat too much during the day as they are sleeping, so that’s also not uncommon.
What’s her set-up like? Maybe changing to a low-sided litter box and adding some hay in different spots will make it easier for her to go in and out and encourage a bit more hay eating?
To me this falls in the “keep an eye on it” category. As long as she is eating normally then I think she just thinks the litter box is comfy.
PS. I would’t increase greens for weight loss, I would reduce pellets as you have, keep greens the same, and do what you can to encourage gentle movement and more hay intake. Adding soft flooring with good traction should help her as well. I really liked using sheepette fabric with my arthritic bun.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.