Mastitis normally only occurs in rabbits that are lactating.

The signs of Mastitis are :

Firm swelling of one or more breasts - which can take on a "blue" appearance
The breasts feel hot
There can be abscess formation within the breast
There may be a foul-smelling discharge from the breast
There may be a blood-stained discharge from the breast
The rabbit may have a poor appetite
High body temperature is present
Death of kits may occur

In severe cases the Doe may develop septicemia which is an
infection in the bloodstream, and will die.
This disease is most often found in rabbits that not kept in a clean environment

Bacteria causing this disease include :

Staphylococcus spp
Streptococcus spp
Pasteurella spp

The infection is thought to reach the breast through a duct in the teat
which carries milk from the gland.
Damage to the teat during suckling by young kits may also cause some contamination
if their environment is kept unsanitary.
Always remember to remove old bedding from rabbit cages and keep them disinfected, especially around the time a doe is due to kindle.