Mastitis is serious (in dogs, cats - and humans), but prognosis is good if treated by a doctor as soon as possible (otherwise it can lead to blood poisoning/infection which can kill). Symptoms include red, discolored, painful, firm or lumpy breast (usually one breast is affected). Also high rectal temperature (above 103 F) in dogs and cats, lack of energy, poor appetite, pus or "dirty" looking milk from that breast. And sometimes dying puppies or kittens. Please take it to the Vet.
