It is a bit difficult, because buns have individual differences. I had abun who was not allowed kale, because he had high blood calcium levels, and kale is a high calcium veg. I wouldn’t have known about his high blood calcium unless he had had bloodwork done. Other buns do just fine on kale, so it’s not really possible to say if kale is all bad or all good for rabbits.

The best thing is to feed a variety of greens, i e to rotate greens. Each new veg should first be introduced in a small quantity. If you rotate greens, you minimise the risk of “over dosing” a certain green. Spinach is one of the greens that are fine if fed sparingly but not recommended for every day use.

The main part of the bun’s diet should be hay, fresh vegetables shouldn’t make up a large part of the daily caloric intake. This is because rabbits are grass eaters and their digestive system (which starts with their teeth)  is adapted to a diet rich in fiber and cellulose. Greens don’t have anywhere near the amount of fiber that grass has, plus greens are very yummy, so a bun that gets lots of greens will eat less hay.

Here is a link to a rather detailed article from the HRS, about greens and fruit for rabbits. As you can see towards the end of the article, the subject of kale is still being debated:

https://rabbit.org/suggested-vegetables-and-fruits-for-a-rabbit-diet/#:~:text=The%20bulk%20of%20fresh%20foods,for%20a%20rabbit%20to%20consume.&text=t%20to%20feed%20would%20be,into%20multiple%20feedings%20a%20day.

The main things to look out for are oxalate content and (sometimes) calcium. Most bunnies can handle lots of calcium, but some need a lower calcium diet, as Bam said, so really you mostly want to look out for oxalate.

Any veggie that is both low in calcium AND low in oxalate could be fed as much as you want. Some examples of this off the top of my head would be lettuces, cilantro, escarole/endive, and I believe bok choy (but it isn’t quite as leafy as I’d like for a staple). High calcium but low oxalate veggies include carrot tops, kale, dandelion, and quite a few herbs. Veggies with high calcium you can and should include, but just keep an eye on your bun’s urine. If it starts looking sludgy, adjust the veggies and chat with your vet. The real thing to limit is oxalate, especially veggies that are both high in oxalate AND calcium (like parsley, spinach, beet greens, chard), because the combo of oxalate and calcium is thought to contribute to crystal formation. These veggies are very nutritious, but should be fed in a rotation and not make up the bulk of the salad, especially spinach, which has super high levels of both oxalate and calcium.

I aim to feed a mix of 3 veggies a day on avg (more or less, depending on the season). I usually have a type of lettuce, an herb, and some other green, with one or none of those being a high-oxalate veg. I also tend to think about things as running averages. If one week I end up feeding more oxalate than I’d like to, the next couple weeks I stick with only low-oxalate veggies.

You’re welcome! It can get overwhelming and there is definitely some conflicting info out there.