Mastitis is a bacterial infection of one or more mammary glands, and in cats it arrives in 2 predictable windows: the first 3 weeks of nursing, and the 2 weeks after a heat cycle in a queen that never had kittens. A firm, hot, painful gland with a rectal temperature above 39.5°C is the pattern that needs a vet the same day. A purple gland, cold patches, or pus with a depressed mother is an emergency: gangrenous mastitis moves in 24 to 48 hours.
Two peak windows, two different mechanisms
During lactation, bacteria climb the teat canal from kittens' mouths or bedding and settle in milk-filled tissue with no drainage. Risk is highest from day 1 to day 21 postpartum, when milk production peaks and the nipples are constantly wet. The second window is hormonal: 1 to 3 weeks after estrus, progesterone drives hyperplasia, the glands swell to 2 or 3 times normal size, and the tissue becomes a culture medium. Queens with cystic endometrial hyperplasia or obesity are overrepresented.
What the gland feels like: 4 findings that set urgency
Cats have 8 glands in 4 pairs, and the 2 inguinal pairs are the usual site. Cup the gland in a flat palm; pinching makes normal tissue feel lumpy.
| Finding | What it suggests | Timeline |
|---|---|---|
| Warm, firm gland, 1 to 2 cm plaque, milk slightly off-color | Early acute mastitis | Vet within 24 hours |
| Gland 2 to 3 times normal size, hard, purple skin, 39.5 to 40.5°C | Severe acute mastitis | Vet today, within 12 hours |
| Fluctuant center, pus at the teat, fever over 40°C | Mammary abscess | Same day, within 6 hours, drainage likely |
| Black or sloughing skin, cold patches, cat refuses to eat | Gangrenous mastitis, sepsis risk | Emergency now, 0 to 30 minutes |
| Firm mass that stays after weaning for 4 to 6 weeks | Hyperplasia, or tumor in a queen over 8 years | Exam within 2 weeks, then cytology |
The 39.5°C line and how to measure it
Normal rectal temperature in a cat is 38.1 to 39.2°C. Use a lubricated digital thermometer, 1 to 2 cm in, held for the full beep, morning and evening. A single reading of 39.5°C in a nursing queen can be normal for the first 48 hours after birth, so repeat it in 2 hours before panicking. A reading of 39.5°C or higher at any other time, or 39.5°C that persists for 2 readings 4 hours apart, means infection until proven otherwise. Never give human fever medicine: paracetamol and ibuprofen are toxic at 1 tablet.
Hot compress: 10 minutes, 3 times a day
Soak a washcloth in water at 38 to 40°C, wring it out, and hold it against the gland for 10 minutes. Work in 2-minute turns if the cloth cools, and re-warm it rather than pressing harder. Three sessions a day is the usual schedule: morning, afternoon, evening, spaced 6 to 8 hours apart. Warm compresses increase blood flow and soften the plaque so milk can move; they do not replace antibiotics, and they are wrong for a pointing abscess. Stop if the cat flinches or vocalizes.
Antibiotics: 10 to 14 days, by prescription only
Every antibiotic for mastitis requires a prescription and an exam; leftover human antibiotics are the wrong drug, the wrong dose, and often the wrong duration. Common choices are amoxicillin-clavulanate at 12.5 to 25 mg/kg every 12 hours, or cephalexin at 20 to 25 mg/kg every 12 hours, for 10 to 14 days. Severe or gangrenous cases get fluids, pain control, and sometimes clindamycin or a culture-guided switch. Give the full course even if the gland feels normal on day 4, because a half course leaves a walled-off focus that flares within 3 weeks. Probiotics 2 hours apart reduce the loose stool of the first 3 days.
Nursing or weaning: the decision in 3 questions
Ask 3 things: is the milk normal in color and smell, is the gland free of pus and blood, and are the kittens gaining weight. A healthy newborn weighs 90 to 110 g and gains 10 to 15 g a day; weigh the litter daily. If all 3 are good, the kittens keep nursing and get antibodies worth having. If the milk is pink, brown, thick, or smells foul, or if the gland has an abscess, stop that side and hand-feed. When only 1 gland is affected, the other 3 pairs still work, so kittens can nurse there while the sick side is stripped by hand every 6 hours to keep it draining.
Hand-feeding when nursing stops
Use a commercial kitten milk replacer, never cow's milk, mixed at the label ratio and fed at 38°C. A newborn takes 5 to 8 mL per feed, 6 to 8 feeds a day, and volume climbs to 10 to 15 mL per feed by week 2 and 20 to 25 mL by week 3. Weigh daily: a kitten that gains less than 7 g in 24 hours for 2 days needs a vet visit. Burp after each feed, keep the kitten upright at 45 degrees, and never squirt milk fast, because aspiration kills faster than underfeeding. Stimulate urination and defecation with a warm damp cloth after every feed for the first 3 weeks.
Abscess, gangrene, and the surgery conversation
An abscess needs drainage, and most queens need sedation for it, plus a 1 to 2 cm opening and flushing with 50 to 100 mL of saline. Gangrenous glands get a mastectomy of the affected chain, plus a spay if she is stable, which removes the hormonal driver. Feline mammary carcinoma is the third possibility, and a mass that persists 4 to 6 weeks after weaning needs cytology, not antibiotics. Queens spayed before 6 months of age have roughly 91 percent lower risk of mammary carcinoma than intact queens.
Do this, in this order
- Take a rectal temperature and write down both the number and the time; repeat in 2 hours if it sits at 39.5°C.
- Feel all 8 glands with a flat palm every morning for the first 3 weeks of nursing, and 2 weeks after any heat cycle.
- Start 10-minute warm compresses 3 times a day, and weigh each kitten daily to see whether milk is moving.
- Book the vet within 24 hours for any firm gland with fever, and the same day for pus, purple skin, or a queen that stops eating.
- Follow the prescribed course for the full 10 to 14 days, and recheck the gland 2 weeks after the last dose.
Rates above come from routine veterinary practice, not a fixed protocol. A queen that is lethargic, breathing fast, or has cold ears needs an ER, because sepsis after mastitis moves in hours, not days. Older queens with recurring lumps are worth a look at arthritis and pain in older cats, since a cat that stops jumping may be guarding a sore gland rather than a joint, and at flea and food allergy when the skin around the nipples is the only thing that is red.
Frequently asked
How do I tell mastitis from normal engorgement in a nursing cat?
Normal engorgement is symmetric, softens after kittens nurse, and comes with a temperature under 39.2°C. Mastitis is usually one gland or one side, feels like a firm 1 to 2 cm plaque that stays hard after nursing, is hot and painful, and comes with a temperature of 39.5°C or higher plus a queen that stops eating or hides from her litter.
Can the kittens keep nursing while the mother is treated?
Yes if the milk looks and smells normal, there is no pus or blood, and the kittens gain 10 to 15 g a day. If the milk is discolored or an abscess is present, stop that side and hand-feed kitten milk replacer at 38°C while stripping the gland by hand every 6 hours. The other three pairs can still feed the litter.
How long does mastitis treatment take in a cat?
Plan on 10 to 14 days of a prescribed antibiotic, with warm compresses 10 minutes three times a day for the first 5 to 7 days. Most queens improve within 48 to 72 hours, but stopping early leaves a walled-off focus that flares within 3 weeks. A firm mass still present 4 to 6 weeks after weaning needs cytology rather than another antibiotic.