Canine Mastitis

Canine mastitis is an infrequent clinical presentation for veterinarians. Most cases present during the time of milk production after puppies’ birth. Cases may also occur when pseudopregnancy occurs in dogs. Of special interest to our patient today is the fact that Great Danes are overrepresented in cases of canine mammary duct ectasia.  Some researchers believe that duct ectasia may predispose female dogs to mastitis. More on that theory shortly.

Mastitis is a word meaning inflammation of the mammary tissue. Mast is the Greek root meaning “breast,” with itis being the suffix that means inflammation. It is generally accepted that most cases of infected mammary tissue in dogs comes from bacteria on the surface of the skin which gain access to the interior of the glands via the pores in the nipples. After puppies’ teeth emerge, around three weeks of age, puncture wounds may also allow entrance of infectious organisms into the mammary tissue. Hematogenous, or blood-borne infection may also deliver bacteria through the circulation to the mammary glands.

Patients present with one or more areas of the breast tissue swollen, hot, discolored and sometimes draining blood and/or pus. After the arrival, treatment and apparent resolution of mastitis in dogs, a subclinical syndrome may occur. There has been insufficient research to determine whether this low-grade, smoldering condition leads to later clinical mastitis. One of the reasons little research is performed on canine mastitis is that it usually responds well to treatment with antibiotic therapy and hotpacking. As a result, we rarely culture the effluent from the gland, and rarely have occasion to obtain histopathology specimens. Interesting aspects of Addison’s case include the fact that she is no longer nursing, hasn’t since early March, and that she is a Great Dane. Mammary duct ectasia is defined as dilatation of collecting ducts with inspissated secretions. Even when mammary glands are not lactating they still secrete. Inspissated refers to material that has become too thickened to flow. If normal non-milk secretions cannot escape the glands and therefore block the ducts, ectasia results. If Addison had mammary duct ectasia prior to this episode, she may have been predisposed to infection at a later time. Indeed, we had observed swellings in her mammary tissue months ago. Because those swellings were neither warm nor painful, we elected to monitor them at each visit. Today’s lesions involve tissues not swollen on those previous visits.

See you Monday, Dr. Randolph.