Mastitis

Outline

Definition
Signalment
Signs
Causes
Risk Factors

BASICS

Definition

Inflammation of the mammary gland most commonly caused by bacterial colonization within the gland; other causes may include neoplasia and mycotic infection.

PATHOPHYSIOLOGY

Initial infection may occur by hematogenous spread, adjacent dermatologic inflammation, or, most commonly, ascending infection via the teat canal. Bacterial colonization of the teat cistern does not always lead to mastitis, which suggests failure of the immune system locally or systemically. Inflammation may involve 1 or several lobes of 1 or both mammary glands. Cellular debris clogs the teat canal and leads to an increase in pressure within the gland, no effective drainage, and the infection may spread to surrounding tissues.

SYSTEMS AFFECTED

Reproductive

INCIDENCE/PREVALENCE

Incidence is low. Protective factors—frequent nursing by the foal, a short lactation period, and small teats.

Signalment

Most cases occur in lactating mares.

Signs

Historical Findings

Reluctance of the mare to allow the foal to nurse, depression, anorexia, and severe adverse behavior when udder is palpated.

Physical Examination Findings

Enlarged or swollen mammary gland
Heat or pain on palpation
Abnormal mammary secretions
Ventral edema
Hindlimb lameness or gait change
Signs of concurrent disease

Causes

Infectious

Bacterial—most commonly Streptococcus zooepidemicus; others include Staphylococcus, Actinobacillus, Pseudomonas, Klebsiella, and Escherichia coli
Fungal—Aspergillus spp. and Coccidioides immitis
Other—aberrant parasitic migration

Noninfectious

Neoplasia—mammary adenocarcinoma.

Risk Factors

Lactation, trauma, or manual manipulation of the teats
Systemic disease that may spread to the mammary gland
Local cellulitis, wounds, or Culicoides hypersensitivity
Recent surgical incision
Compromised foals or mares that require hand-milking

Diagnosis ⬆ ⬇

Outline

Differential Diagnosis
CBC/Biochemistry/Urinalysis
Imaging
Other Diagnostic Procedures

DIAGNOSIS

Differential Diagnosis

Other Causes of Mammary Heat, Pain, or Abnormal Secretions

Abscess may be differentiated from diffuse mastitis by palpation or US. The udder may be painful if transiently distended, but this should resolve completely with stripping of the udder.

Other Causes of Abnormal Udder Development

Placentitis, impending parturition, or abortion.

CBC/Biochemistry/Urinalysis

Leukocytosis with neutrophilia, hyperfibrinogenemia, increased SAA, or anemia of chronic disease possible.

Imaging

Other Diagnostic Procedures

Samples from each teat cistern should be collected aseptically and submitted for aerobic culture and cytologic examination for definitive diagnosis. Gram-stain preparations of mammary secretions or milk may guide initial treatment. Anaerobes are not significant bacterial pathogens. Cytologic examination of milk—often acellular or contains rare neutrophils from normal, lactating mares; contains macrophages with vacuoles present (foam cells) and lymphocytes in the drying-off period; shows numerous intact and degenerated neutrophils and cellular debris, and may show large numbers of bacteria or fungal hyphae with mastitis. Mammary gland biopsy indicated if clinical signs are not responsive to initial treatment for bacterial infection, or if cytologic examination is not suggestive of infectious mastitis.

Treatment ⬆ ⬇

TREATMENT

Frequent stripping out of the affected lobes
Hot packing
Hydrotherapy
Light exercise, to decrease edema formation
Surgery to establish drainage from a mammary abscess, or mammectomy to remove suspected neoplasia

Medications ⬆ ⬇

Outline

Drug(s) of Choice
Alternative Drugs

MEDICATIONS

Drug(s) of Choice

Antimicrobial agent is dictated by culture and sensitivity
Trimethoprim–sulfadiazine (30 mg/kg every 12 h)—effective in 75% of cases; administer pending culture and sensitivity results. Penicillin with an aminoglycoside is effective in most cases (procaine penicillin 22 000 units/kg IM every 12 h, gentamicin 8.8 mg/kg IM every 24 h)

Alternative Drugs

Clean and disinfect teat orifice prior to local infusions with lactating cow intramammary treatments. Use caution—equine teat canal is smaller and shorter than the bovine.

Follow-up ⬆ ⬇

Outline

Patient Monitoring
Possible Complications

FOLLOW-UP

Patient Monitoring

Palpate udder and take rectal temperature daily. Treatment should continue for a minimum of 5–7 days or until 24 h after signs have resolved. If abnormalities in the peripheral blood exist, repeat CBC, fibrinogen, or SAA. Renal function should be monitored with long-term aminoglycoside and nonsteroidal administration.

Possible Complications

Sepsis, bacteremia, endotoxemia, laminitis, colitis, lymphadenopathy, lymphangitis, and fibrosis of the affected mammary glands with subsequent decreased milk production.

section name header

Basics ⬇

Diagnosis ⬆ ⬇

Treatment ⬆ ⬇

Medications ⬆ ⬇

Follow-up ⬆ ⬇

Miscellaneous ⬆ ⬇

Suggested Reading ⬆ ⬇

Author(s) ⬆