Mastitis is inflammation of breasts and commonly results from a bacterial infection of the milk producing glands in the breasts. It can also be due to trauma to the lactating gland. E. coli, Staphylococci, and β-hemolytic Streptococci are the most common bacteria involved. In some cases it can lead to septic shock and could be fatal. This condition mainly affects postpartum bitches, but can also occur in pseudo-pregnant lactating bitches too.
Some common symptoms associated are loss of appetite, lethargy, firm, swollen, warm, and painful mammary gland(s) from which pus or hemorrhagic fluid can be expressed, neglect of puppies due to pain when attempting to nurse, failure of puppies to thrive, fever, dehydration, and septic shock with systemic involvement, and abscesses or gangrene of the gland(s), if left untreated