THE MERCK VETERINARY MANUAL
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Mastitis in Small Animals

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Mastitis is inflammation of the mammary gland(s) associated with bacterial infection. It occurs in postpartum bitches and less commonly in postpartum queens. Rarely, mastitis is seen in lactating pseudopregnant bitches. Risk factors for developing mastitis include poor sanitary conditions, trauma inflicted by offspring, and systemic infection. Mastitis may be acute or chronic.

Mastitis may be localized (eg, involving a single gland sinus), diffuse in a single gland, or diffuse within multiple glands. The animal may be asymptomatic or critically compromised. Milk from mastitic glands may appear normal grossly or may be abnormal in color or consistency. In acute mastitis, the affected glands are hot and painful. If acute mastitis progresses to septic mastitis, signs of systemic illness such as fever, depression, anorexia, and lethargy may be seen, and the dam may neglect the neonates. In chronic or subclinical mastitis, the main complaint may be failure of offspring to thrive.

Diagnosis is usually evident from the history and physical examination. Microscopic examination of milk may reveal inflammatory cells. Milk from each gland should be evaluated in any postpartum bitch or queen with signs of systemic illness. Before beginning therapy, a milk sample should be collected (or obtained by fine-needle aspiration) for bacterial culture and sensitivity. Culture of milk or fluid expressed from the affected glands yields moderate to heavy growth of Escherichia coli or staphylococci.

Broad-spectrum, bactericidal antibiotics should be chosen based on sensitivity tests and with the understanding they will be passed in the milk to the young. Antibiotics such as tetracycline, chloramphenicol, or aminoglycosides should be avoided during lactation unless the neonates are weaned. Cephalexin (5–15 mg/kg, PO, tid) and amoxicillin/clavulanate (14 mg/kg, PO, bid-tid) are recommended as initial therapeutic agents pending culture results. Hot-packing the affected gland encourages drainage and seems to relieve discomfort. Fluid therapy is indicated in animals with septic mastitis that are dehydrated or in shock. An abscessed mammary gland should be lanced, drained, flushed, and treated as an open wound.

Nonseptic mastitis is seen most commonly at weaning. The affected glands are warm, swollen, and painful to the touch, but the animal is alert and healthy. Warm compresses should be applied to the affected glands 4–6 times daily, and the young should be encouraged to nurse from these glands. When galactostasis occurs at weaning, lactation can be diminished by reducing food and water intake of the dam. The mammary glands should not be stimulated during this time. Appropriate food and water must be provided for the young.

Last full review/revision November 2013 by Mushtaq A. Memon, BVSc, PhD, DACT

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