Sorry to contradict LBJ10 but collards and kale are relatively high in calcium. Bok choy is a bit lower though.
Here’s an older article that lists calcium content in various veggies (kale and collards are listed as “good” sources of calcium in this case, as the focus was on providing calcium):
https://drive.google.com/file/d/1cO2b1ht51a6zie8kbSqafNevnv88xdZB/view?usp=sharing
You can also look up various greens nutrition facts if you aren’t sure. One of my buns is prone to get a bit sludge with certain greens. With him I stick to mostly lettuce, endive or escarole, cilantro, and then a small amount of a higher calcium veg such as bok choy or kale, but I don’t feed kale daily or in large amounts. Cilantro, endive, and romaine are great daily feeders (and are my go-to’s) as they are low in both oxalate and calcium.
Also, here’s an interesting perspective by Dr. Frances Harcourt Brown: https://www.harcourt-brown.co.uk/articles/free-food-for-rabbits/calcium-and-rabbit-food
Because veggies have a lot of water, they can be really important in flushing excess calcium out, and rabbits get a lot of calcium from hay and their pellet feed. That’s not to say that veggies don’t make a difference though, because I def notice a difference in my bun’s pee when he gets a lot of calcium-rich veggies!
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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.