If your rabbit runs free around your garden or in a large run they must not eat ivy as it’s very toxic to them and will cause some serious health issues.
Ivy is a plant that grows across most of Europe and can survive a lot of different weather conditions. I advise checking everything your rabbits can possibly come across in your garden.
Domestic rabbits aren’t good at chosen what they can or cannot eat, unlike their more worldly wild counterparts. Don’t just assume they will not eat anything that is toxic to them.
Do a detailed sweep of your garden and clear out any plants you’re unsure about, and certainly those like ivy that you know are a potential health hazard.
Keep your bunnies on a strict diet of good quality hay, some formulated pellets, plenty of fresh water, and some delicious leafy greens and vegetables. It’s not hard to keep rabbits healthy and happy, it’s veering off and trying to spoil them that causes problems.