# Mastitis in Dogs: Signs, Causes, and Treatment Options Mastitis in dogs is an inflammation of one or more mammary glands that most often appears in the days and weeks after whelping. The classic picture is a bitch that was nursing normally and then develops a hot, swollen, painful gland, milk that looks discolored or clotted, and puppies that cry, lose weight, or become lethargic. Acute septic mastitis is a medical emergency for the whole litter because bacteria and bacterial toxins pass into the milk and can cause septicemia in newborns [1]. Chronic and subclinical mastitis are quieter, sometimes showing only poor puppy weight gain or a gland that never fully empties [2][3]. This guide walks through how to recognize mastitis, how to distinguish it from galactostasis and from mammary tumors, what your veterinarian will test, and how treatment and nursing management work together. A short triage summary follows, then the detail. **Owner-facing triage summary** - One swollen, hot, painful gland with discolored milk, plus a fever or a depressed bitch: call your veterinarian today. This is acute mastitis until proven otherwise. - Puppies that are crying, cold, weak, not gaining weight, or have diarrhea: treat this as an emergency for the litter as well as the mother [1]. - A firm, painless, movable lump in a gland with no heat, no pain, and normal milk: this is more consistent with a mammary tumor and needs a veterinary examination and cytology, not antibiotics [4]. - Engorged, uncomfortable glands with normal-looking milk and a comfortable bitch: this may be galactostasis, which often responds to frequent milking and warm compresses, but it can progress to mastitis [5]. - Never give leftover human or veterinary antibiotics from your cupboard, and never give human mastitis medications to a dog. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## At a Glance: Mastitis, Galactostasis, and Mammary Neoplasia The three conditions below are the most common reasons a postpartum bitch is presented with a mammary complaint. They overlap in some features, which is why examination and testing matter. | Feature | Acute septic mastitis | Galactostasis | Mammary neoplasia | |--|--|--|--| | Typical timing | Around 1 to 3 weeks postpartum, average day 16.7 in one large cohort [5] | First days after whelping, or after a missed feeding | Any age, more common in middle-aged to older intact bitches | | Gland feel | Hot, swollen, firm, very painful | Engorged, tense, uncomfortable but not usually hot | Firm, often painless, movable nodule or mass | | Milk appearance | Discolored, brownish, purulent, flaky, clotted, or bloody [6] | Normal milk, may drip or leak | Normal milk unless the tumor distorts the duct | | Bitch systemic signs | Fever, lethargy, inappetence, dehydration, vomiting | Usually none | Usually none unless the tumor is advanced or ulcerated | | Puppy signs | Crying, poor weight gain, diarrhea, weakness, sepsis [1] | Hungry puppies, poor let-down, weight plateau | Usually none from the tumor itself | | Key diagnostic step | Milk cytology and [bacterial culture](/blog/guides/bacterial-culture) and sensitivity [2][6] | Physical exam, response to milking | Fine needle aspirate or biopsy [4] | | First-line management | Antibiotics guided by culture, warm compresses, frequent milking, puppy support [1][4] | Warm compresses, frequent milking, ensure all glands drain | Surgical assessment, staging, possible excision [4] | ## What Mastitis Is and Why the Postpartum Bitch Is at Risk The canine mammary gland is a chain of ducts and lobules embedded in fat, arranged in two rows along the ventral chest and abdomen. During lactation the gland is highly vascular, actively secreting, and open to the outside through the teat canal. That open teat canal is the doorway for bacteria. Most canine mastitis is ascending: organisms climb the teat canal into the duct system, multiply in milk, and provoke an inflammatory response in the gland wall [6]. In an experimental model where Staphylococcus intermedius was inoculated directly into a gland on day 8 after whelping, all six bitches developed clinical mastitis, with glands becoming painful, hot, enlarged, and edematous, and secretion turning brownish and purulent before becoming yellowish and thick [6]. That sequence mirrors what owners see at home. Mastitis is common enough that any breeding practice should expect it. In a retrospective study of two guide dog colonies covering 3,076 whelpings, clinical mastitis was diagnosed in 13.2 percent of whelpings, with the average day of diagnosis at 16.7 days postpartum [5]. A separate systematic review reported a prevalence of 0.71 percent in the general bitch population, which likely reflects underdiagnosis in pet dogs where mild cases are never presented [7]. The gap between those numbers is the point: many cases are mild, missed, or dismissed as "just engorgement." Two risk factors stand out from the guide dog data. Bitches with mammary gland congestion were 4.8 times more likely to develop mastitis than bitches without congestion, and bitches with litters of nine or more puppies were about 60 percent more likely to develop mastitis than bitches with smaller litters (16.2 percent versus 11.3 percent) [5]. Both findings make biological sense. Congestion means milk is not moving, and a large litter means high demand, frequent nursing, and more opportunities for teat trauma. ## Causes of Mastitis in Dogs ### Bacterial infection Bacteria are the dominant cause. Staphylococcus aureus is the most frequently isolated organism from canine milk in recent culture surveys, accounting for roughly 55 percent of positive cultures in one study of 156 milk samples from 39 bitches [2]. Staphylococcus intermedius has been used experimentally to reproduce the disease [6], and beta-hemolytic Streptococcus has been documented causing clinical mastitis that seeded fatal neonatal sepsis in a litter of Pug puppies [1]. Escherichia coli is another important player. E. coli is a major cause of acute clinical mastitis in cattle, and the same organism is a leading cause of urinary tract infection and [pyometra in dogs](/knowledge/veterinary-medicine/clinical-methods/canine-pyometra-diagnosis-surgical-management), which means the postpartum genital tract and the mammary gland can share a common source of contamination [8]. Less common but important bacterial causes include Brucella suis, which has been documented in a bitch with dystocia, abortion, and mastitis, and was isolated from milk in that case [9]. Brucella is a zoonotic concern and changes how the case is managed, including handling of milk and puppies [9]. Mycobacterium kansasii has been reported causing pyogranulomatous mastitis in a dog with a mammary mass and a history of demodicosis and pseudopregnancy [10]. ### Fungal and algal causes Fungal mastitis is rare but real. Blastomyces dermatitidis has been reported in three dogs with mammary lesions initially suspected to be neoplasia or postpartum bacterial mastitis, and two of the three also had lymph node and pulmonary involvement [11]. Mammary candidiasis with embolic dissemination has been described in a postpartum dog that had repeated episodes of intermittent mammary disease and a neurological syndrome, with Candida albicans cultured from lesions in multiple organs [12]. Prototheca species, algae best known for causing mastitis in farm animals, have caused disseminated disease in dogs [13]. These organisms matter because they do not respond to standard antibacterial therapy, and a case that fails to improve on appropriate antibiotics deserves a second look. ### Galactostasis and milk stasis Galactostasis is the accumulation of milk in a gland that is not being emptied. It is not an infection by itself, but it is the setup for one. Stagnant milk is a culture medium, and congestion was the strongest single risk factor for subsequent mastitis in the guide dog cohort [5]. A bitch with a large litter, a puppy that cannot nurse effectively, a teat that is malformed or blocked, or a mother that is uncomfortable and reluctant to let puppies feed will all develop stasis. ### Trauma and poor hygiene Teat trauma from sharp puppy claws, bite wounds from puppies, and unsanitary whelping boxes all increase bacterial load at the teat orifice. Sager and Remmers noted that in intensively operated breeding kennels, bacterial infections were a significant contributor to perinatal mortality, and that subclinical mastitis of the bitch was a second important source of infection leading to septicemic death of newborns [3]. Their recommendations included bacteriological examination of the milk before the expected whelping date in high-risk kennels [3]. ### Immune and metabolic factors The postpartum period is metabolically demanding. Serum ionized calcium has been studied in breeding bitches in relation to mastitis, metritis, and dystocia, and no significant differences in ionized calcium were found between bitches that did and did not develop mastitis at any sampled time point [14]. This is useful because it means hypocalcemia is not a reliable explanation for a mastitis case, and calcium supplementation is not a treatment for mastitis. ## Signs of Mastitis in Dogs ### Local signs in the gland The affected gland becomes painful, hot, enlarged, and edematous [6]. The bitch may pull away when a puppy nurses or when you touch the gland. The skin over the gland can look red or dusky. In severe cases the gland becomes dark, cold, and necrotic, which is gangrenous mastitis [15]. Gangrenous mastitis has been reported in a bitch after dystocia, with marked leukocytosis and falling platelet counts during the critical phase [15]. ### Milk changes Milk from an affected gland is the single most useful thing an owner can look at. In experimentally induced staphylococcal mastitis, secretion became brownish and purulent with flakes or clots, then turned yellowish and thick [6]. Any milk that is discolored, watery, bloody, clotted, or foul-smelling should be treated as abnormal. ### Systemic signs in the bitch Fever, lethargy, inappetence, dehydration, vomiting, and a swollen painful abdomen are all possible. Severe mastitis can progress to septic shock and death of the bitch [7]. A bitch that is depressed and not caring for her puppies is a serious case. ### Puppy signs Puppies are often the first clue. Maternal clinical and subclinical mastitis is one of the main sources of neonatal infection, because puppies ingest milk containing bacteria and bacterial toxins, a pattern known as toxic milk syndrome [1]. In a documented case, three 5-day-old Pug puppies presented with diarrhea, body erythema, and omphalitis, and their blood counts showed leukopenia with neutropenia and monocytosis, while the bitch had purulent content in all mammary glands [1]. Milk culture grew beta-hemolytic Streptococcus. Puppies that cry persistently, feel cold, stop gaining weight, develop diarrhea, or become weak need immediate veterinary attention alongside their mother. ## How Veterinarians Diagnose Mastitis ### Physical examination Your veterinarian will examine every gland, not just the one you noticed. They will palpate for heat, swelling, pain, and firm nodules, express milk from each gland to assess color and consistency, take the bitch's temperature, and assess hydration and mentation. They will also ask about whelping history, litter size, puppy weight gain, and how long the problem has been present. ### Milk cytology Milk cytology is the fastest way to confirm inflammation in the gland. The Whiteside test and Giemsa-stained smears of mammary secretion were used in the experimental model, where the Whiteside test was positive in 41 of 46 samples from inoculated glands and neutrophils predominated during the acute stage [6]. Cytology also helps distinguish septic inflammation from other processes. In one case, cytology of a mammary aspirate revealed macrophages containing acid-fast rods, which pointed toward mycobacterial infection rather than ordinary bacterial mastitis [10]. In another, cytology of purulent mastitis identified intralesional fungal hyphae, which redirected the diagnosis toward candidiasis [12]. ### Bacterial culture and sensitivity Culture and sensitivity should be performed before antibiotics are started whenever possible. This matters because resistance is common. In a study of Staphylococcus aureus isolates from canine milk, 51 percent of isolates met the criteria for biofilm formation, and resistance-associated genes were detected by PCR [2]. Biofilm-forming organisms are harder to clear and may need longer or different therapy. Culture also identifies the organism, which matters when the cause is Brucella, a fungus, or an alga rather than a routine staphylococcus [9][12][11][13]. ### Bloodwork and imaging A complete blood count and chemistry panel assess systemic involvement. In the experimental model, blood leukocyte counts increased while platelet counts decreased [6]. In the gangrenous mastitis case, leukocytosis ranged from 25,200 to 48,600 per microliter with platelets falling to 107,000 to 179,000 per microliter, and both returned to normal with treatment [15]. Platelet number and pattern may help gauge severity [15]. Ultrasound can be useful. In normal lactating glands, tissue layers are easily distinguished, while inflamed glands lose distinct layering and inflamed regions have reduced echogenicity [16]. Doppler assessment of blood vessel density may carry prognostic information, since bitches with reduced central vessel density had a poor outcome while those with increased density had a good outcome in one small series [16]. ### When to suspect a tumor instead Mammary tumors are typically firm, painless nodules rather than hot, painful, swollen glands, and they do not usually come with fever or abnormal milk [4]. A fine needle aspirate or biopsy distinguishes them. This distinction is not always clean. One reported case involved a bitch with a progressively enlarging, painful, pendulous cystic mammary swelling that turned out to contain microfilariae of Dirofilaria immitis, and histology also found solid carcinoma in a small area of the mass [17]. Another case began as a one-centimeter mammary mass that cytology revealed to be mycobacterial mastitis [10]. When a mammary mass does not behave like a simple tumor, infection and unusual organisms belong on the list. ## Differentiating Mastitis from Mammary Tumors Owners frequently ask whether a lump is mastitis or cancer. The practical approach is to look at four things: pain, heat, milk, and the bitch's general condition. Mastitis in dogs produces a painful, hot gland with abnormal milk and often a sick bitch. Mammary neoplasia produces a firm, painless nodule with normal milk and a well bitch, at least early on [4]. Galactostasis produces an engorged, uncomfortable gland with normal milk and a comfortable bitch. When the picture is mixed, testing decides. Milk cytology and culture answer the infection question. Fine needle aspiration of a discrete mass answers the tumor question. Ultrasound helps characterize the gland and can be repeated to track response [16]. If a mass is present and the bitch is not lactating, infection is less likely and neoplasia more likely, but both can coexist. ## Treatment Options for Mastitis in Dogs ### Antibiotics guided by culture Antibiotic choice should follow culture and sensitivity results whenever possible. In the documented neonatal sepsis case, milk culture grew beta-hemolytic Streptococcus that was sensitive to cephalosporins and penicillins, the puppies were treated with ceftriaxone, and the mother was treated with amoxicillin with potassium clavulanate, with both responding and blood counts normalizing after 7 days of treatment [1]. That case illustrates the principle: identify the organism, match the drug, treat long enough, and recheck. Do not use leftover antibiotics, and do not use human mastitis medications. Some antibiotics are safe in lactation and some are not, and the choice depends on the organism and the bitch's status. Your veterinarian will select a drug that is appropriate for a nursing mother or will advise separating puppies if needed. ### Supportive care at home Warm compresses and frequent milking of the affected gland are the backbone of home management. The goal is to move milk out of the gland so that bacteria and toxins do not sit in stagnant secretion. Gently express the affected gland every few hours, or allow puppies to nurse if your veterinarian approves and the milk is being monitored. Keep the whelping area clean and dry. Offer fresh water and encourage eating. A bitch that will not eat or drink needs veterinary attention. ### Pain control Mastitis is painful, and a painful bitch may refuse to let puppies nurse, which worsens stasis. Your veterinarian will choose an analgesic that is safe during lactation. Never give human pain relievers, since several common ones are toxic to dogs. ### Managing the puppies Puppy management is as important as treating the mother. In the documented sepsis case, the puppies were separated from their mother, fed a breast milk substitute, and treated with antibiotics [1]. Separation is sometimes necessary when the milk is heavily contaminated or the mother is too ill to nurse. If puppies stay with the mother, weigh them at the same time every day, watch for diarrhea, crying, coldness, and weakness, and contact your veterinarian at the first sign of trouble. Puppies that develop sepsis need their own treatment, not just their mother's. ### When surgery is needed Gangrenous mastitis, abscessation, and glands that do not respond to medical therapy may require surgical drainage or mastectomy. In the gangrenous mastitis case, the bitch was critically ill with marked leukocytosis and platelet abnormalities, and recovery followed treatment that included addressing the infected gland [15]. Surgery is also part of the plan when a mammary mass is present alongside infection [4]. ### Special situations Brucella suis infection requires combination antibiotic therapy. In the reported cases, dogs responded favorably to rifampicin and doxycycline, with individually tailored regimens based on presentation, owner compliance, and zoonotic risk assessment [9]. Brucella is zoonotic, so handling of milk, placentas, and puppies changes, and your veterinarian will advise on precautions [9]. Fungal and algal mastitis require antifungal or specific antimicrobial therapy rather than routine antibiotics [12][11][13]. ```mermaid flowchart TD A[Postpartum bitch with mammary problem] --> B{Is the gland hot painful and swollen} B -->|Yes| C[Check milk color and consistency] B -->|No| D{Firm painless nodule} D -->|Yes| E[Fine needle aspirate for tumor] D -->|No| F[Consider galactostasis] C --> G{Is milk abnormal} G -->|Yes| H[Milk cytology and culture] G -->|No| F H --> I[Antibiotics guided by culture] I --> J[Warm compresses and frequent milking] J --> K[Monitor puppies daily] K --> L{Puppies unwell} L -->|Yes| M[Separate and treat puppies] L -->|No| N[Recheck with veterinarian] ``` ## Unsafe Home Remedies and Common Mistakes Several mistakes make canine mastitis worse. - Giving antibiotics without culture. This risks the wrong drug, resistance, and a missed diagnosis such as Brucella, a fungus, or an alga [9][12][11][13]. - Applying human mastitis advice. Human guidelines do not apply to dogs, and human medications can be toxic. - Stopping antibiotics early. The bitch may look better in a few days, but the gland needs full treatment and a recheck. - Ignoring the puppies. Even a mild maternal mastitis can seed neonatal sepsis [1][3]. - Assuming every lump is mastitis. Firm, painless nodules are more consistent with tumors and need cytology [4]. - Delaying veterinary care for a depressed bitch. Severe mastitis can progress to septic shock and death [7]. ## Prevention Prevention focuses on milk flow, hygiene, and early detection. - Keep the whelping area clean and dry, and change bedding frequently. - Check every gland daily for the first three weeks postpartum, since the average day of diagnosis in one large cohort was 16.7 days [5]. - Express or allow nursing from every gland so that none stays full. Congestion is the strongest identified risk factor for mastitis [5]. - Weigh puppies daily. Poor weight gain is an early sign of milk problems. - In high-risk kennels, consider bacteriological examination of milk before the expected whelping date, as recommended in breeding kennel studies [3]. - If a bitch has had mastitis before, plan for closer monitoring in the next lactation. ## Prognosis Prognosis depends on how quickly treatment starts and how severe the case is. Most bitches with uncomplicated acute mastitis recover well with appropriate antibiotics and supportive care. The documented neonatal sepsis case had full recovery of both mother and puppies after 7 days of treatment [1]. The Brucella cases responded favorably to combination therapy [9]. Severe gangrenous mastitis carries a much worse prognosis and can be fatal to the bitch [7][15]. Doppler ultrasound findings of reduced central blood vessel density have been associated with poor outcome in a small series, which supports early imaging in severe cases [16]. Puppy survival depends on early recognition and treatment of neonatal infection [1][3]. ## Limitations and When to Contact a Veterinarian This article is educational and is not a substitute for veterinary diagnosis or treatment. Individual cases vary, and your veterinarian needs to examine your dog. Contact a veterinarian immediately if any of the following apply: - The bitch has a fever, is lethargic, will not eat, is vomiting, or seems painful when you touch her abdomen. - A gland is dark, cold, or black, which suggests gangrenous mastitis [15]. - Milk is discolored, bloody, clotted, or foul-smelling. - Puppies are crying, cold, weak, not gaining weight, or have diarrhea [1]. - The bitch has not improved after 48 hours of treatment. - You see a firm, painless lump in a gland, with or without lactation [4]. - The bitch has a history of Brucella exposure, feral pig hunting, or travel to an endemic area [9]. - The bitch has recently whelped and has a history of dystocia, abortion, or retained placenta [9]. ## Frequently Asked Questions ### What are the first signs of mastitis in a dog? A hot, swollen, painful mammary gland with discolored milk is the classic first sign. Many owners also notice the bitch pulling away when puppies nurse or a puppy that stops gaining weight. ### Can mastitis in dogs go away on its own? Mild galactostasis can resolve with frequent milking and warm compresses, but true bacterial mastitis usually needs antibiotics. Waiting risks progression to severe disease and infection of the puppies. ### How do I tell mastitis from a mammary tumor in my dog? Mastitis is painful and hot with abnormal milk, while mammary tumors are typically firm, painless nodules with normal milk. Your veterinarian can confirm with cytology or a fine needle aspirate. ### Are the puppies at risk if the mother has mastitis? Yes. Puppies can ingest bacteria and toxins in the milk and develop neonatal sepsis. Watch for crying, coldness, diarrhea, weakness, and poor weight gain, and contact your veterinarian right away. ### Should I keep letting puppies nurse if the mother has mastitis? Ask your veterinarian. In some cases nursing is allowed with monitoring, and in others the puppies need to be separated and fed a milk substitute while the mother is treated. ### How long does treatment for mastitis in dogs take? Treatment typically continues for at least a week, and the bitch should be rechecked. In one documented case, mother and puppies responded fully after 7 days of antibiotics. ### Can I use human mastitis medicine for my dog? No. Human mastitis medications and leftover antibiotics are not appropriate for dogs and can be harmful. Your veterinarian will select a drug that is safe for a nursing bitch. ### Will my dog get mastitis again in her next litter? She may. Bitches with mammary congestion and large litters are at higher risk, so plan for closer monitoring of every gland in the next lactation and discuss prevention with your veterinarian. ## Related Articles - [Cat Diarrhea with Worms: Causes and Treatment Options](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-diarrhea-worms-causes-treatment) - [Cat Skin Infection: Signs and Treatment Options](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-skin-infection) - [Dog Hair Loss on Ears: Causes and Treatment Options](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/dog-hair-loss-on-ears) - [Cat Hair Loss on Legs: Causes and Treatment Options](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-hair-loss-on-legs-causes-and-treatment-options) - [Dog Skin Rash on Legs: Causes and Treatment Options](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/dog-skin-rash-on-legs-causes) - [Chinchilla Respiratory Infections: Causes, Signs, and Treatment](/knowledge/veterinary-medicine/small-mammal-care/chinchilla-respiratory-infections-causes-signs-treatment) - [Feline Gingivitis: Causes, Signs, and Treatment](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/feline-gingivitis-causes-signs-and-treatment) ## Sources 1. 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