INTRODUCTION

Mastitis is a condition that primarily affects the postpartum bitch. Occasionally pseudopregnant, lactating bitches will be affected. The anatomy of the teat includes a teat orifice, teat canal, teat sinus, and gland sinus (Figure 142-1).¹ Additionally each gland sinus is separated by connective tissue. Therefore mastitis can be diffuse, among multiple glands, or localized within one gland. The clinical picture can vary widely from life-threatening sepsis to no apparent clinical signs.

Figure 142-1 Anatomy of the canine mammary glands.

From Evans HE, Christensen GC: The urogenital system. In Evans HE, editor: Miller’s anatomy of the dog, ed 3, Philadelphia, 1993, Saunders, with permission.

ETIOLOGY

The etiology is largely unknown. Risk factors include hematogenous spread, poor hygiene, environmental conditions, and trauma from the neonates. Although there are no published data on breed predisposition, it appears that breeds with short legs and pendulous mammary glands are at greater risk of trauma. The bacteria most typically cultured are Escherichia coli, staphylococci, and β-hemolytic streptococci.^2-4

CLINICAL PRESENTATION

The clinical picture can vary from critically ill to asymptomatic with a history of the neonates failing to thrive. The affected gland or glands may be hot, swollen, firm, and painful. Severely affected cases can manifest fever, depression, lethargy, and anorexia. Some animals may arrive in septic shock. Abscess formation or gangrene is sometimes noted in severe cases of mastitis.

DIAGNOSIS

Normal canine milk can vary from yellow (colostral milk) to white, depending on the length of time post whelping. Milk from bitches with mastitis may appear normal, purulent, or reddish brown. The cytology of normal milk is very cellular, containing large numbers of neutrophils and macrophages.² Therefore it is important to interpret cytology with care. Smears from bitches with mastitis will be cellular but will have many free and engulfed bacteria.

Systemically ill patients may have alterations in the complete blood count and chemistry panel. It is not uncommon to see leukocytosis with a left shift or, in septic patients, leukopenia. Dehydration may cause elevations in packed cell volume, total protein, and blood urea nitrogen.