Mushrooms are fleshy, spore-bearing fruiting body of a fungus, which are typically produced above ground on soil or on its food source.
So can rabbits eat mushrooms at all?
Let’s take a look at their nutritional data in particular their sugar, calcium, fat, phosphorus, sodium and acidic content
Nutritional value per 100 g (3.5 oz)
Energy 94 kJ (22 kcal)
Thiamine (B1) (9%)0.1 mg
Riboflavin (B2) (42%)0.5 mg
Niacin (B3) (25%)3.8 mg
Pantothenic acid (B5)
Vitamin C (0%)0 mg
Calcium (2%)18 mg
Phosphorus (17%)120 mg
Potassium (10%)448 mg
Sodium (0%)6 mg
Zinc (12%)1.1 mg
Link to USDA Nutrient Database entry
As you can see mushrooms contain a lot of phosphorus, a lot of acidic content, and a hint of fat.
This means that they can’t eat mushrooms at all. They just have too much bad stuff in them and will hurt them if they eat them.
This includes all forms of mushrooms, whether cooked or raw, or even found in the wild. They are just too dangerous for bunnies.