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Causes of Nipple Discharge in Dogs

Updated on October 08, 2015
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Adrienne Farricelli is a former veterinary hospital assistant and now a certified dog trainer, behavior consultant, and author of dog books.

What causes nipple discharge in dogs.
What causes nipple discharge in dogs.

Table of Contents

1) Understanding Nipples in Dogs

2) Did Your Know?

3) Why Does My Dog Have Nipple Discharge?

4) For Further Reading

5) Comments

Did you know?

Mammary glands are modified sweat glands that are present in both male and female embryos during fetal development. The nipples remain indistinguishable at birth, until when sex hormones kick into high gear and the female hormones develop them in such a way as to have a secretory function.

Understanding Nipples in Dogs

If you noticed nipple discharge in your dog, you might be concerned because you may have heard that this can be cancer. While cancer is always a possibility, there are several other causes for nipple discharge in dogs. You will therefore need to see your vet for proper diagnosis and treatment. This article is only meant to give an idea of what can cause nipple discharge in dogs as only your vet can determine exactly what your dog has.

First of all, a lesson in dog anatomy. Consider that all dogs have nipples. Male dogs, female dogs, spayed dogs, neutered dogs and, of course, intact dogs. In female dogs, the nipples have an important function; that is, to deliver milk that is produced in the mammary glands so to nourish a batch of hungry puppies.

The mammary glands in dogs are arranged in two rows starting from the chest area all the way up to the groin. Interestingly, according to University of Illinois, the number of glands varies based on the dog's size. While in general dogs may have anywhere between 8 to 12, with 4 to 6 on each side, large breeds are known for having about ten, while smaller breeds are known for having about eight.There are no rules written in stone though as you may sometimes encounter dogs with some extras nipples or some dogs with some missing. If you want to learn more about where they're located, consider that generally large breeds have the following:

  • 1 pair of cranial thoracic teats
  • 1 pair of caudal thoracic teats
  • 1 pair of cranial abdominal teats
  • 1 pair of caudal abdominal teats
  • 1 pair of inguinal teats

Each nipple is surrounded by several openings that are meant to allow milk to excrete when the puppy suckles. You would assume that since male dogs don't have to whelp, Mother Nature would have deprived them of nipples. Instead, just like human men, male dogs have nipples, but they are typically in a rudimentary state. So since the primary purpose of nipples is to excrete milk, it's quite normal to be alarmed when you notice a discharge that takes place when dogs aren't lactating.

A case of mastitis in sheep.
A case of mastitis in sheep. | Source
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Why Does My Dog Have Nipple Discharge?

Nipple discharge is more commonly seen in intact female dogs, but spayed female dogs and male dogs may also develop conditions that may cause discharge.

End of Pregnancy

When dogs are nearing the end of pregnancy, their nipples may develop a discharge. The discharge is typically clear or milky in color. The onset time of milk production in dogs varies from one another. Some start developing milk even a week prior, others a day or two prior to give birth and others right after giving birth. When a dog gives birth, oxytocin, the primary hormone associated with labor and delivery, is what triggers lactation and the "let-down" of milk, explains Gen B., a retired veterinarian.


Remember the openings we talked about where milk is secreted for the pups when they suckle? While these openings have an important purpose, one must consider that these same openings may also allow bacteria to enter. It's a good idea to keep an eye on mother dog's nipples. It's not uncommon for mother dog to develop mastitis, the medical term for an infection of the dog's milk producing glands. It's often caused by the puppy's nails scratching the nipples or unsanitary conditions. Symptoms include hot, painful mammary glands, and a pus/bloody discharge from nipples. Mother dog may also become reluctant to nurse. If you suspect your nursing dog has mastitis, see your vet and make sure the puppies don't nurse from the affected nipple as in severe infections the milk can cause serious illness and even death of the puppies. Left untreated, mother dog may develop a fever, loss of appetite and lethargy.

False Pregnancy

A phenomenon owners of intact female dogs must keep in consideration is what is known as "false pregnancy." After a female, intact dog goes in heat, she may develop maternal behaviors such as nesting along with physical signs that are strikingly similar to a real pregnancy. The physical signs include enlarged mammary gland along with nipple discharge, and in some cases, even abdominal distension .This occurs because after a dog's heat, the dog's body will produce high level of progesterone regardless if she is pregnant or not. Generally, signs of false pregnancy develop about a month or two after the dog's heat. Typically, in a dog undergoing false pregnancy, the discharge is seen from multiple nipples at the same; which is quite different from mammary cancer which mostly affects only one, explains veterinarian Dr. K. See your vet to rule out a possible pregnancy or a possible pyometra (infection of the uterus).

An Abscess

In this case, we are talking about an abscess that could have developed as a result of an injury or intrusion of a foreign body. For instance, an abscess may form as a result of a foreign body such as a thorn or small stick that may have introduced bacteria into the skin by the dog's nipple/mammary gland. Then, the puncture closes over, trapping the bacteria inside. This causes local swelling, warmth and sometimes discharge.

Mammary Gland Cancer

Intact, non-spayed dogs are more commonly affected than spayed dogs as they undergo hormonal changes that raise and fall. In dogs who were spayed before the first heat cycle, the chances for developing breast cancer are significantly low, just about 0.5%. Chances are also extremely rare in male dogs. However, the statistics grow higher in female dogs spayed after 2 years of age. When it comes to statistics, 50 percent of dog breast cancer cases are benign, while the remaining 50 percent are not. Non-benign breast cancer in dogs is cancer that has spread to other locations such as the lymph nodes, lungs (causing coughing, labored breathing) or other body parts. Generally, the larger the growth, the bigger the chances that cancer has spread, explains Dr. Daniel A. Degner,a board-certified veterinary surgeon. Symptoms of breast cancer in dogs include a straw-colored, pus-like or bloody discharge from the nipple and presence of small or large nodules within the dog's breast. Mammary tumors are most often seen in the inguinal glands close to the legs. Breast cancer is diagnosed by fine needle aspiration. Here are some typical findings:

  • Fibroadenoma: A benign glandular tumor
  • Mixed Mammary Tumor: as the name implies, these can be either benign or malignant.
  • Adenocarcinoma: malignant
  • Inflammatory Carcinoma: highly malignant ulcerated tumor that spreads quickly and produces pus and discomfort, but luckily, not very common.

As seen, discharge from the nipples in dogs can be caused by various conditions. Some conditions may be easily treated, others are more serious. See your vet if your dog has fluid coming from her nipples.

Disclaimer: this article is not to be used as a substitute for professional veterinary advice. If your dog has nipple discharge see your vet for proper diagnosis and treatment.

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    • DDE profile image

      Devika Primić 17 months ago from Dubrovnik, Croatia

      Interesting and most informative. I learned a lot from here on this topic.

    • profile image

      Sthefany 9 months ago

      Omg,, thank u so much. I was freaking out that something was wrong with my little girl. Thank god it is just a false pregnancy. ;-)

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