... It looks like either a botfly or a maggot hole ... What I do is a spray their pans with a mixture of teatree oil and a citrus and vodka (or witch hazel or everclear) LOL. But also, fans and fly tape around/near cages. 50 rolls of fly tape for $9 from amazon. Does wonders
Wow. These look very similar to something on my pup that the Vet said was "just hotspots". They were scabs when I saw them. One was about a half inch and two were about a quarter inch. He peeled the scabs off and they were very red and bloody looking. Gave the pup some antibiotics and an antibiotic/antifungal spray and they are going away. I don't know if that's what your rabbits have but he said they happen when an animal gets wounded (puppies bite each other, rabbits sometimes do too) and then the wound gets infected. It can also be self inflicted from serious scratching. Like others have said, you can treat with an antibiotic and antifungal medication, however, I'd ask a Vet before treating your feeders because some of these should not be used on animals that are destined to be eaten.
that's not botfly I don't think. BUT to test out the theory that it IS botfly... apply some vaseline to it. If a warble comes out (due to not being able to breathe) pull it out SLOWLY AND CAREFULLY!
as I've been thinking about this and how it seems to be contagious.. I"m thinking it's fungal, so treat with something anti-fungal. OR cull the whole lot early. Wear some gloves, fungal stuff tends to be contagious to various life forms.