NAVLE Reproductive

Feline Mastitis Study Guide

📅 March 28, 2026 ⏱ 25 min read

Mastitis is an inflammatory condition of one or more mammary glands, typically caused by bacterial infection.

Overview and Clinical Importance

Mastitis is an inflammatory condition of one or more mammary glands, typically caused by bacterial infection. While relatively uncommon in cats compared to dogs, mastitis represents a clinically significant condition that can rapidly progress to life-threatening sepsis or gangrenous tissue necrosis if not promptly diagnosed and treated. The condition occurs almost exclusively in lactating queens during the postpartum period, though it may also develop secondary to feline mammary fibroepithelial hyperplasia (FEH) or pseudopregnancy. Understanding the etiology, clinical presentation, and treatment options for feline mastitis is essential for NAVLE preparation and clinical practice.

Gland	Location	Blood Supply	Lymphatic Drainage
T1	Cranial thoracic	Internal thoracic a.	Axillary LN (cranial only)
T2	Caudal thoracic	Internal thoracic a.	Axillary or Inguinal LN
A1	Cranial abdominal	Cranial superficial epigastric a.	Axillary or Inguinal LN
A2	Caudal abdominal/Inguinal	Caudal superficial epigastric a.	Inguinal LN (caudal only)

Feline Mammary Gland Anatomy

Cats normally have four pairs of mammary glands (8 total) arranged in two parallel chains along the ventral abdomen. The glands are designated based on anatomical location as T1 (cranial thoracic), T2 (caudal thoracic), A1 (cranial abdominal), and A2 (caudal abdominal/inguinal). Each nipple contains 5-7 lactiferous pores with 1-3 openings on the tip and the remainder on the sides.

Mammary Gland Nomenclature and Blood Supply

High-YieldThe caudal mammary glands (A1, A2) are most commonly affected by mastitis and are also the most common sites for mammary neoplasia. The intermediate glands (T2, A1) have dual lymphatic drainage to both axillary and inguinal lymph nodes, which has surgical implications for mastectomy planning.

Organism	Characteristics	Clinical Significance
Escherichia coli	Gram-negative; facultative anaerobe; normal GI flora	Endotoxin release can cause sepsis, SIRS, and multiorgan failure; common cause of gangrenous mastitis
Staphylococcus aureus	Gram-positive; normal skin flora; most commonly isolated	Beta-lactamase production common; can cause abscessation
Streptococcus spp.	Gram-positive; environmental and skin flora	Often causes acute mastitis; generally antibiotic-responsive

Etiology and Pathophysiology

Types of Mastitis

Septic Mastitis: Caused by bacterial infection of the mammary gland, typically through ascending infection via the teat canal during nursing. Bacteria may also enter through wounds, scratches from nursing kittens, or hematogenous spread from other infection sites (e.g., metritis).

Non-Septic (Galactostatic) Mastitis: Results from milk accumulation in the mammary gland without bacterial infection. Occurs during sudden weaning, death of a kitten, or when fewer kittens nurse than the queen can support. Galactostasis can progress to septic mastitis if untreated.

Common Bacterial Pathogens

Predisposing Factors

Trauma from nursing kittens (sharp teeth, claw scratches)
Galactostasis (milk stasis from sudden weaning or kitten death)
Unsanitary nursing environment
Feline mammary fibroepithelial hyperplasia (FEH)
Immunocompromise (stress, poor nutrition, concurrent illness)
Hematogenous spread from metritis or other infection
Large litters (constant nursing) or small litters (insufficient milk removal)

Severity	Clinical Signs
Early/Subclinical	Mild mammary gland swelling; slight discomfort on palpation Kittens fail to gain weight appropriately Queen may be asymptomatic
Acute/Moderate	Affected gland(s): firm, hot, swollen, painful, erythematous Abnormal milk: thick, discolored, bloody, or purulent Systemic signs: fever, lethargy, anorexia, dehydration Queen may refuse nursing or be aggressive toward kittens
Severe/Gangrenous	Mammary gland appears purple/black (necrosis) Skin ulceration, abscessation, tissue sloughing Foul-smelling discharge Signs of sepsis: tachycardia, tachypnea, hypothermia, collapse Potentially fatal without aggressive intervention

Clinical Signs and Presentation

High-YieldPoorly growing or failing-to-thrive kittens may be the ONLY early indication of subclinical mastitis. Daily kitten weights are essential for early detection. Kittens should gain approximately 10-15 grams per day in the first two weeks of life.

Test	Findings in Mastitis	Clinical Utility
Milk Cytology	Increased WBCs (greater than 3000 cells/mcL); degenerate neutrophils; intracellular or free bacteria	Confirms inflammatory response; quick, inexpensive; highly diagnostic
Bacterial Culture and Sensitivity	Identifies specific pathogen and antibiotic susceptibility pattern	Essential for refractory cases; guides targeted antibiotic therapy
CBC	Neutrophilic leukocytosis with left shift; degenerative changes in sepsis	Assesses severity of systemic involvement
Serum Biochemistry	May show azotemia, hypoglycemia, electrolyte imbalances in sepsis	Evaluates systemic illness; guides fluid therapy
Ultrasound	Loss of normal gland architecture; fluid pockets (abscess); heterogeneous echotexture	Identifies abscess formation; assesses extent of involvement

Diagnostic Approach

Physical Examination

A thorough physical examination is essential. Palpate all mammary glands systematically, comparing bilateral symmetry. Assess for heat, firmness, swelling, pain, and discoloration. Attempt to express milk from affected glands to evaluate character (normal milk should be white/cream-colored with thin consistency).

Diagnostic Testing

NAVLE TipIn most cases, mastitis can be diagnosed presumptively based on signalment (lactating queen), history (postpartum period), and physical examination findings (hot, swollen, painful mammary gland). Milk cytology confirms the diagnosis by revealing degenerate neutrophils with intracellular bacteria.

Condition	Key Differentiating Features	Signalment/History
Feline Mammary Fibroepithelial Hyperplasia (FEH)	Rapid, diffuse, bilateral mammary enlargement; non-painful initially; no milk production; progesterone-dependent	Young intact queens (cycling/pregnant); cats on progestins; can develop secondary mastitis
Mammary Neoplasia	Firm, nodular mass(es); may be ulcerated; adherent to underlying tissue; 85-90% malignant in cats	Older intact queens (mean 10-12 years); not lactating; Siamese predisposed
Galactostasis	Firm, distended glands without heat or marked pain; queen otherwise well; milk appears normal	Recent weaning; kitten death; can progress to septic mastitis

Differential Diagnosis

High-YieldFibroepithelial hyperplasia (FEH) can coexist with mastitis! When FEH becomes ulcerated or secondary infection develops, it presents with both the massive gland enlargement typical of FEH AND signs of infection. Treatment requires addressing both the progesterone influence (with aglepristone or OVH) AND the bacterial infection.

Antibiotic	Dosage	Coverage	Notes
Amoxicillin-Clavulanate	12.5-25 mg/kg PO q12h	Gram-positive and negative; beta-lactamase producers	FIRST-LINE choice; safe for nursing kittens; excellent milk penetration
Cephalexin	15-30 mg/kg PO q8h	Gram-positive; some gram-negative	Good alternative; safe for nursing kittens
Enrofloxacin	5 mg/kg PO q24h	Broad-spectrum including Pseudomonas	Reserve for culture-confirmed; AVOID in nursing queens (cartilage damage in kittens)

Treatment and Management

Antimicrobial Therapy

Broad-spectrum antibiotics should be initiated immediately while awaiting culture results. Selection must consider milk penetration, safety for nursing kittens, and coverage of common pathogens. Duration is typically 2-3 weeks, extending 5-7 days beyond clinical resolution.

NAVLE TipAVOID tetracyclines, chloramphenicol, and aminoglycosides in nursing queens as they can harm nursing kittens (teeth staining, bone marrow suppression, ototoxicity, respectively). Amoxicillin-clavulanate is the safest first-line choice.

Supportive Care

Warm compresses: Apply to affected glands 3-4 times daily to promote drainage and relieve discomfort
Hand-milking: Gently express infected glands every 6 hours to prevent milk stasis and encourage blood flow
Continued nursing: If milk is not grossly purulent or foul-smelling, kittens can continue nursing from affected glands (this promotes drainage)
Pain management: NSAIDs (meloxicam 0.1 mg/kg PO q24h) for analgesia and anti-inflammatory effects
Fluid therapy: SC or IV fluids for dehydrated or septic patients
Nutritional support: High-calorie diet to maintain lactation and support immune function

Management of Severe/Gangrenous Mastitis

Severe mastitis with abscessation or gangrene requires aggressive intervention:

Hospitalization with IV fluids and IV antibiotics
Surgical debridement of necrotic tissue
Open wound management with lavage (dilute betadine or chlorhexidine)
Honey dressings may be used for antibacterial properties and granulation tissue promotion
Mastectomy may be required for severely necrotic glands
Kitten removal: Wean kittens and hand-raise with milk replacer; monitor daily weights

When to Continue Nursing	When to Wean/Hand-Raise
Mild mastitis without systemic illness Milk is not grossly abnormal Queen allows nursing Kittens are maintaining weight Non-affected glands available	Grossly purulent or foul-smelling milk Gangrenous or abscessed glands Queen refuses nursing due to pain Kittens losing weight or ill All glands severely affected

Kitten Management During Mastitis

High-YieldContinued nursing is actually BENEFICIAL in uncomplicated mastitis as it promotes milk drainage and blood flow to the affected gland. The antibiotics in the milk and ingestion of bacteria are generally safe for kittens. However, kittens should be supplemented if milk production is inadequate.

Prognosis

Good prognosis: Most cases of uncomplicated mastitis respond well to appropriate antibiotic therapy and supportive care. Clinical improvement is typically seen within 48-72 hours, with complete resolution in 2-3 weeks.

Guarded prognosis: Cases with sepsis, gangrenous involvement, or systemic illness carry increased risk. Septicemia secondary to E. coli endotoxin release can trigger multiorgan failure and may be fatal despite aggressive treatment.

Prevention

Maintain clean, sanitary nursing environment
Trim kitten claws regularly to prevent nipple trauma
Ensure adequate nutrition for lactating queen
Monitor kitten weights daily during nursing period
Gradual weaning rather than abrupt cessation
Examine mammary glands daily during postpartum period
Spaying: The most effective prevention is ovariohysterectomy for queens not intended for breeding

"MASTITIS" Mnemonic for Clinical Signs:

M - Mammary gland swelling (hot, firm, painful)

A - Anorexia in the queen

S - Systemic signs (fever, lethargy, dehydration)

T - Thick or discolored milk

I - Infection confirmed by cytology (degenerate neutrophils, bacteria)

T - Thriving kittens are NOT (failure to gain weight)

I - Ignore unaffected glands (can continue nursing from these)

S - Staph, Strep, and E. coli (the "S-S-E" pathogens)

"ACE" First-Line Antibiotics:

Amoxicillin-clavulanate (first choice) - Cephalexin (good alternative) - Enrofloxacin (avoid in nursing queens)

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