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Canine mastitis is an infection or inflammation of the mammary glands — most common in nursing mothers during the first weeks after whelping, though it can occasionally affect females after a heat cycle (and rarely, spayed dogs or males). Caught early it responds well to treatment; missed, it can progress to abscesses, gangrenous tissue and a seriously ill dog within days. Here is what to watch for.
Signs of Mastitis in Dogs
- One or more mammary glands that are swollen, firm, hot or painful to the touch
- Discolored skin over the gland — red early, purple or dark in severe cases
- Milk that looks off: yellowish, brown, blood-tinged or thick
- A mother reluctant to nurse, or crying puppies that fail to gain weight (often the first sign)
- Fever, lethargy, refusal to eat, vomiting as infection advances
What Causes It
Bacteria — usually E. coli, Staphylococcus or Streptococcus — enter through the teat canal or small scratches from puppy nails and teeth. Risk factors: poor whelping-box hygiene, oversupply of milk after weaning or losing puppies, trauma to the glands, and a run-down immune system after the demands of pregnancy and nursing.
Veterinary Treatment
Mastitis needs a vet — same-day if the gland is dark, the mother is feverish, or puppies aren’t gaining. Treatment typically includes antibiotics safe for nursing, pain relief, and in abscessed or gangrenous cases, surgical drainage. Your vet will advise whether puppies can keep nursing (usually yes on the healthy glands, and often on treated glands depending on the antibiotic) or need supplemental feeding.
Home Care That Helps Recovery
- Warm compresses on the affected gland 2-4 times daily, with gentle expression of milk to relieve pressure
- Cabbage leaf wraps — a traditional vet-endorsed trick for reducing swelling and discomfort, changed every few hours
- Keep nursing or milking the gland (per your vet) — emptying the gland clears the infection faster than resting it
- Hygiene — clean bedding daily, trim puppy nails weekly
- Support mom’s recovery — antibiotics plus the metabolic strain of nursing hit the gut hard; a liquid probiotic for dogs helps restore gut flora during and after treatment, and daily immune support drops can help a depleted mother rebuild resilience. Watch her stools — our diarrhea guide covers antibiotic-related upset.
Prevention for Future Litters
Clean, dry whelping area; trim puppy nails from week 2; check glands daily during nursing (you’ll catch mastitis days earlier by feel than by behavior); and wean gradually to avoid milk stasis. For timing context around pregnancy and whelping, see our canine gestation period guide. More whelping and health guides at Dog Health Insider.
Scientific References
- Wiebe VJ, Howard JP. Pharmacologic advances in canine and feline reproduction. Top Companion Anim Med. 2009;24(2):71-99. (PubMed)
- Jutkowitz LA. Reproductive emergencies. Vet Clin North Am Small Anim Pract. 2005;35(2):397-420. (PubMed)
- Vasiu I, Dąbrowski R, Martinez-Subiela S, et al. Milk C-reactive protein in canine mastitis. Vet Immunol Immunopathol. 2017;186:41-44. (PubMed)
Mastitis can progress quickly — always consult your veterinarian at the first sign of a hot, painful or discolored mammary gland.