Mold -- of any type -- can be harmful to rabbits. Mold likes damp/moist places...including manure on farmland. It is important that
any greens or hay or even food pellets are free from any mold before feeding it to rabbits.
Not all carrot tops will have Alternaria (or any other mold) on them. It depends on where they came from and how they've been stored.
It is a good caution, however, to be diligent in checking greens thoroughly for any signs of mold before offering them to a rabbit.
Here is some further info regarding mold poisoning:
Mycotoxin or mold poisoning, unfortunately, is detected pretty late and by that time it’s done its damage. To make things even more difficult, rabbits are good at hiding their symptoms so you might not know that they’re sick, to begin with. Nevertheless, if you keep a close eye on your rabbit then you may be able to identify certain symptoms that come with mold poisoning.
- Your rabbit will lose their appetite and that will result in drastic weight loss. Some rabbits might accept food initially and then reject it and some might simply refuse the food outright.
- Your rabbits will be in clear abdominal pain.
- They will suffer from sudden upset tummies which will include loose stool.
- Sores around the mouth and face.
- Discharge coming out from the eyes.
- Fever. A low body temperature lower than 101F is too low and is a cause of concern.
- Changes in their reproductive cycle especially in unspayed female rabbits.
- There will also be blood present in their poop. This is the most serious symptom that indicates that it is too late.
These are just the visible signs; you can also determine moldy toxicity through testing. For that, you will need to visit your vet who will run the kidney, liver, and blood function tests.
If you do manage to detect mold poisoning in its early stages, your rabbit may still have a chance to survive. You will need to rush them to a vet who will probably use intravenous fluid to the toxins out of their system. They may also give drugs and sucralfate to treat internal bleeding and ulcers. (taken from link below)
https://petschoolclassroom.com/can-rabbits-die-from-mold/