Mastitis in Dogs: Mammary Gland Infection

Quick Answer
  • Mastitis is inflammation and usually infection of one or more mammary glands, most often in dogs that are nursing or recently weaned.
  • Common signs include a swollen, firm, hot, painful gland; red, purple, or bruised skin; and milk that looks cloudy, bloody, thick, or pus-like.
  • Many mild cases improve with outpatient care such as oral antibiotics, pain control, warm compresses, and careful gland drainage under your vet’s guidance.
  • Severe cases can progress to abscesses, tissue death, or sepsis. If your dog is lethargic, feverish, vomiting, refusing food, or the gland looks black or cold, see your vet immediately.
  • Puppies may still be able to nurse in some cases, but that decision depends on the gland appearance, the mother’s condition, and the medication plan from your vet.
Estimated cost: $150–$2,500

What Is Mastitis?

Mastitis is inflammation of the mammary gland, and in dogs it is most often linked to bacterial infection during lactation. It usually affects a mother dog after giving birth, especially in the first days to weeks postpartum, but it can also happen after sudden weaning, with milk buildup, or less commonly in dogs with pseudopregnancy.

The condition can range from localized and uncomfortable to life-threatening. In milder cases, one gland may be swollen, warm, and painful while the mother otherwise seems fairly normal. In more serious cases, the gland can become severely infected, form an abscess, or lose blood supply. When tissue starts to die, the gland may turn dark purple, blue, or black and the dog can become systemically ill.

There are a few patterns your vet may discuss. Acute mastitis causes obvious pain, swelling, and abnormal milk. Subclinical mastitis may be harder to spot and may first show up as puppies that are crying, hungry, or not gaining weight well. Gangrenous mastitis is the most severe form and is an emergency.

Prompt veterinary care matters for two reasons: protecting the mother and protecting the litter. A dog with mastitis may need help with pain control, infection management, and decisions about whether puppies should continue nursing, switch glands, or receive supplemental feeding.

Signs of Mastitis in Dogs

  • One or more mammary glands that feel swollen, firm, or hard
  • Heat, redness, or obvious tenderness of the gland
  • Milk that is cloudy, thick, yellow, green, brown, blood-tinged, or pus-like
  • Pain when puppies nurse or when the area is touched
  • Ulceration, scabbing, or discharge from the nipple area
  • Mother dog avoiding puppies, snapping, or refusing to lie still for nursing
  • Fever, lethargy, poor appetite, or vomiting in more severe cases
  • Puppies crying often, nursing poorly, or failing to gain weight
  • A gland that looks purple, blue, black, or feels cool instead of warm
  • Signs of dehydration or collapse in the mother dog

Some dogs with early mastitis still seem bright and alert, so the first clue may be the litter rather than the mother. Puppies that are not gaining weight, seem constantly hungry, or crowd only certain glands may be telling you something is wrong. Check the mammary chain daily during nursing and call your vet if any gland becomes painful, discolored, or produces abnormal milk.

See your vet immediately if your dog has fever, vomiting, marked lethargy, refuses food, or if any gland turns dark purple or black. Those changes can signal severe infection, abscess formation, or gangrenous mastitis.

What Causes Mastitis?

Most canine mastitis starts when bacteria move up through the teat canal and into the mammary gland. Common bacteria include Escherichia coli, Staphylococcus spp., and Streptococcus spp. These organisms may come from the skin, the puppies’ mouths, or the environment.

Small injuries make infection more likely. Puppies’ nails can scratch the skin around the nipples, and vigorous nursing can irritate the teat opening. Dirty bedding, damp whelping areas, and fecal contamination also increase bacterial exposure. Even without obvious trauma, a heavy bacterial load can overwhelm the gland’s normal defenses.

Milk stasis is another major factor. When milk is not removed regularly, the gland becomes engorged and inflamed, which can set the stage for infection. This may happen with a small litter, sudden puppy loss, abrupt weaning, or when puppies strongly prefer some glands and ignore others.

Not every case is purely infectious. Some dogs develop inflammatory mastitis related to trauma or milk accumulation without a clear bacterial cause. Pseudopregnancy can also lead to mammary enlargement and milk production, which may increase the risk of secondary infection if milk sits in the gland.

How Is Mastitis Diagnosed?

Your vet will usually start with a physical exam and a close look at every mammary gland. The pattern of swelling, heat, pain, skin color, and milk appearance often gives strong clues. Because some dogs have more than one affected gland, a full mammary exam matters.

Milk cytology is commonly used to look for inflammatory cells and bacteria. A milk culture and susceptibility test may be recommended if the infection is severe, recurrent, or not improving as expected. That helps your vet choose an antibiotic that is more likely to work and is appropriate for a nursing mother when possible.

Bloodwork may be advised if your dog seems sick overall. A complete blood count can help assess infection and inflammation, while chemistry testing can look for dehydration or organ stress in more serious cases. If an abscess or deeper pocket of infection is suspected, your vet may also recommend ultrasound.

Diagnosis is not only about confirming mastitis. Your vet also needs to decide how sick the mother is, whether puppies are getting enough nutrition, and whether nursing should continue from the affected gland, continue only from unaffected glands, or pause while the litter is supported another way.

Treatment Options for Mastitis

Spectrum of Care means you have options. Here are treatment tiers at different price points.

Outpatient care for mild, localized mastitis

$150–$450
Best for: Dogs with one or two affected glands who are still bright, eating, hydrated, and not showing signs of sepsis or tissue death
  • Veterinary exam
  • Milk evaluation with or without cytology
  • Oral antibiotics selected by your vet
  • Pain relief and anti-inflammatory medication as appropriate
  • Warm compresses several times daily
  • Guidance on gentle hand-milking or drainage if advised
  • Home monitoring of the mother’s appetite, temperature, and comfort
  • Daily puppy weight checks and nursing plan review
Expected outcome: Often very good. Many uncomplicated cases improve within days and resolve over about 2 to 3 weeks with timely treatment and close follow-up.
Consider: This approach depends on reliable home care. Some dogs worsen quickly, and puppies may still need supplementation if milk production drops or nursing becomes too painful.
Most Common

Medical management with diagnostics and close rechecks

$450–$1,200
Best for: Moderate cases, dogs with fever or reduced appetite, multiple affected glands, recurrent mastitis, or cases not improving on first-line outpatient treatment
  • Exam plus bloodwork
  • Milk cytology and bacterial culture with susceptibility testing
  • Injectable or stronger initial medications when needed
  • Fluid support for dehydration or fever
  • Targeted pain control
  • Recheck exam in 2 to 5 days
  • Puppy supplementation plan or temporary nursing restrictions if needed
  • Monitoring for abscess formation or worsening skin changes
Expected outcome: Good in many dogs when treatment is started before tissue damage becomes severe. Some glands may have reduced future milk production.
Consider: Higher cost range and more visits. Puppies may need bottle or tube-feeding support, and the mother may need temporary separation from the litter depending on comfort and milk safety.

Hospitalization and surgery for abscessed, necrotic, or septic cases

$1,200–$2,500
Best for: Dogs with gangrenous mastitis, abscesses, severe systemic illness, rapidly spreading infection, or mammary tissue that has become black, cold, or nonviable
  • Emergency exam and stabilization
  • IV fluids and injectable antibiotics
  • Hospital monitoring for sepsis, pain, and hydration
  • Imaging if abscess or deep tissue involvement is suspected
  • Surgical drainage or debridement of infected tissue
  • Partial or complete mastectomy of nonviable gland tissue when necessary
  • Postoperative wound care and bandage changes
  • Full litter feeding plan if nursing cannot continue
Expected outcome: Guarded to fair, depending on how quickly treatment starts and whether sepsis is present. Survival is possible with aggressive care, but the affected gland may be permanently lost.
Consider: This is the most intensive option and often requires hospitalization, surgery, and hand-rearing or supplementing puppies. Recovery can be more demanding during an already stressful postpartum period.

Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.

Questions to Ask Your Vet About Mastitis

Bring these questions to your vet appointment to get the most out of your visit.

  1. You can ask your vet whether this looks like mild mastitis, an abscess, or possible gangrenous change.
  2. You can ask your vet if the puppies can safely nurse from the affected gland, only from unaffected glands, or if they need supplementation.
  3. You can ask your vet which antibiotic is being used, why it was chosen, and what side effects to watch for in both mom and puppies.
  4. You can ask your vet whether milk cytology or culture would help guide treatment in this case.
  5. You can ask your vet how often to use warm compresses and whether hand-milking is appropriate for this gland.
  6. You can ask your vet what warning signs mean the infection is spreading or becoming an emergency.
  7. You can ask your vet how often the puppies should be weighed and what amount of daily weight gain is expected for this litter.
  8. You can ask your vet when a recheck should happen and whether future breeding or nursing from that gland may be affected.

Preventing Mastitis in Nursing Dogs

Prevention starts with daily observation. During lactation, check each mammary gland for swelling, heat, pain, and changes in milk appearance. Early mastitis is easier to manage than advanced infection, and sometimes the first sign is poor puppy weight gain rather than obvious illness in the mother.

Keep the whelping area clean, dry, and frequently bedded with fresh material. Trim puppy nails regularly to reduce scratches around the nipples. If one gland seems overly full or puppies strongly favor certain teats, talk with your vet about ways to improve even milk removal and reduce engorgement.

Avoid abrupt weaning when possible. A gradual transition lowers the risk of painful milk buildup. If a puppy dies, is removed from the litter, or the litter size is small, monitor the mother closely because milk stasis can develop quickly.

Good postpartum support also matters. Nursing dogs need adequate calories, water, rest, and follow-up care. If your dog is not intended for future breeding, spaying after recovery can prevent future pregnancy-related lactation problems and also lowers the risk of some reproductive diseases.

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