Disorders of Canine Mammary Glands

Most canine mammary tumors occur in females over 7 years old.
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You are probably fearing the worst after feeling a big lump while petting your dog's belly. Most canine mammary gland disorders cause local swelling, so this symptom doesn't necessarily mean there's cancer. Mammary gland problems are common in female dogs but can occur to dogs of either gender.


Mastitis is infection of one or more mammary glands. Common culprits include the Staph and E. coli bacteria, although other pathogens can cause similar symptoms. The condition emerges when bacteria enter through the openings on a dog's nipple and infiltrates the mammary gland. The area around the affected gland may swell up and feel warm to the touch. Some infections force bacteria-laden pus into the milk reservoir, so don't waste time getting the mom and pups to the vet if you think she has mastitis. If she has puppies, they should be able to feed as normal as long as Mama still has a few healthy glands and the energy to care for her offspring. Ask your vet for instructions on puppy care when the mom is sick.


The canine species is no stranger to mammary tumors. Tumors of the mammary gland account for about half of all tumors reported in female dogs. A female dog is three times more likely to develop them than women are, making them the most vulnerable species to this disorder, according to the website of the UC Davis School of Veterinary Medicine. Slightly less than half of mammary tumors are malignant. Surgery is the standard treatment for these tumors and is often effective, although it's impossible to guarantee a permanent recovery when malignant cancer is involved. Having your pet fixed before she enters her first reproductive cycle significantly reduces the chances of her developing mammary cancer later in life.

Lactation Disorders

A female dog may have false pregnancies that cause her body to prepare for puppies though she's not pregnant. A natural imbalance of hormones is often to blame for the suddenly swollen mammary glands and unusual nesting behavior. Luckily, most false pregnancy cases go away without human intervention in about two weeks, according to United States Kerry Blue Terrier Club website. Some mother dogs develop a condition called galactostasis when milk builds up inside their glands. Many cases emerge immediately after the mom's puppies are weaned. This disorder causes some swelling and pain, so your vet may prescribe something to ease your pet's discomfort.


While you may not be able to tell the difference between a cyst and a tumor, lab tests on the fluid drawn from the mass usually can. There's a good chance the lump you felt on your dog's stomach was actually a cyst, a benign pocket of skin filled with fluid or fat. Cyst development may be associated with fluctuations in your pet's hormone levels. They aren't particularly dangerous, although they can be uncomfortable if multiple cysts exist or if one gets too big. Ask your vet for advice regarding treating your dog's cysts.