I think it’s fine! Veggies with high calcium and oxalate are fine to feed in rotation, and even one week of maybe too much of one thing isn’t the end of the world, it’s more of a cumulative thing.
Since arugula is low oxalate and the mizuna is higher, that’s still only 1 high oxalate veg, so that’s a good combo. Mustard greens/mizuna are also high in vitamin A, which is a good thing. 🙂
The calcium debate is interesting. Rabbits do need a lot of calcium and excrete excess in their urine. Usually you only need to worry about calcium if your bun is prone to sludge or has had kidney issues. I’ve also noticed personally that veggies like kale seem to produce more sludge than other high calcium veggies. Maybe just because kale tends to be a lot more voluminous. At the shelter we definitely notice more calcium in urine when we feed a lot of kale.
So if you were concerned about calcium you could keep an eye on her urine output and make sure it’s nice and liquid.
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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.