Disorders of the Mammary Glands

1) Are bitches with a history of false pregnancy more likely to suffer from pyometra than bitches that never had false pregnancy?

The signs of false pregnancy are a consequence of the normal hormonal changes all dogs undergo when they go through heat. Because all dogs go through these changes, whether or not they show signs of false heat, and because it is these hormonal changes that are associated with development of pyometra, dogs with signs of false pregnancy are not more likely to get pyometra than are bitches that never show signs of false pregnancy. In fact, I like a history of false pregnancy because it gives me historical evidence that hormonal changes occurred as expected in that bitch.

2) Will spaying cure false pregnancy? How about having a litter?

No. The clinical signs of false pregnancy are due to a lack of progesterone. Removing the ovaries and uterus will not increase progesterone concentrations in the body. Spaying will, however, keep the bitch from ever having false pregnancy again because she will never go through heat again. Having a litter will not decrease signs of false pregnancy after subsequent heat cycles and may increase mammary development and milk production.

3) Is spaying protective against breast cancer in dogs?

Yes, bitches that have been spayed are less likely to develop mammary cancer when aged than are bitches that are not spayed. The protective effect is greater if the bitches are spayed younger, with the greatest effect seen in bitches spayed before they ever go through heat.


Mastitis is inflammation and infection of the mammary glands. It may occur occasionally as a component of false pregnancy (see below) but most commonly occurs postpartum, during peak lactation ().



Agalactia is lack of milk production after whelping ().

False Pregnancy


False pregnancy is poorly named. All dogs that go through estrus go through a false pregnancy because all undergo the same hormone changes after estrus whether they are bred or not. The disorder called false pregnancy is the combination of physical and behavioral changes exhibited by some nonpregnant dogs about 2 months after estrus and should therefore be called false whelping. However, false pregnancy is the common term and will be used in this text. False pregnancy sometimes is called pseudocyesis or pseudopregnancy.

After estrus, or standing heat, all dogs go through a 2-month-long diestrus during which concentrations of progesterone are high (). At the end of diestrus, progesterone concentrations in blood fall rapidly and concentrations of prolactin begin to rise. The prolonged high progesterone stimulates mammary development and may loosen joints, allowing some dogs to develop apparent abdominal distension as their ribs “spring” apart more. The sudden fall in progesterone and rise in prolactin stimulate milk production and behaviors of whelping, such as nesting and protection of offspring. Although all dogs undergo these hormonal changes, not all bitches exhibit clinical signs. Some describe bitches undergoing hormonal changes with no associated clinical signs as having covert false pregnancy, whereas those exhibiting signs have overt false pregnancy.

Wild dogs live in packs and over time all the bitches in the pack cycle together, often seasonally. Most of the animals in the pack are related. If a bitch is not high enough in the pack to be bred and does not become pregnant, exhibition of signs of false pregnancy may allow her to nurse pups that are genetically similar to her. Overt false pregnancy may be an evolutionary adaptation to assist animals in continuance of their genetic line, whether or not they are bred.

Signs of false pregnancy can be induced by anything that causes a precipitous fall in progesterone in the blood. Dogs spayed while in diestrus will undergo a rapid fall in progesterone as their ovaries and the progesterone-producing tissue on them is removed. Animals treated with progesterone as a therapy may go through false pregnancy when progesterone treatment is stopped.

Animals with a history of overt false pregnancy after estrus are not more prone to develop pyometra than are dogs without obvious clinical signs of false pregnancy. Concentration of progesterone in blood does not differ significantly between the two groups. In fact, I like a history of false pregnancy because that implies that at those cycles in which false pregnancy signs were seen, the bitch ovulated and maintained high progesterone concentrations for the expected amount of time.

The mammary development and lactation associated with overt false pregnancy may allow secondary invasion of bacteria and mastitis. Mastitis occurs much more commonly in postpartum bitches that are nursing puppies but was reported to be associated with false pregnancy in 31% of 104 cases of mastitis reported in one study. Recent work suggests that animals exhibiting overt false pregnancy may be more prone to mammary neoplasia when aged, perhaps because of tissue damage during development, distension, and regression of the mammary glands.


All intact bitches may show signs of false pregnancy. No age or breed predisposition has been reported.

History and clinical signs

Some bitches show overt signs of false pregnancy when they are young and stop as they age, whereas others will not show signs of false pregnancy until they are older. It is reported that 87% of bitches show signs of false pregnancy two or more times in their life while intact. Most bitches presenting with overt false pregnancy had gone through proestrus and estrus 1 to 3 months before presentation. The occasional bitch has been spayed recently or has just completed progesterone therapy. History of behavioral changes seen may include nesting, protection of inanimate objects such as pillows and stuffed animals, and aggression. Changes in appetite may occur. The mammary glands often are distended, and serous fluid or normal-appearing milk can be expressed (). Galactorrhea is the medical term for inappropriate milk production. If secondary mastitis is present, the mammary glands are enlarged, hot, and painful to the bitch. All else is normal.


False pregnancy should be differentiated from true late-term pregnancy even in bitches not known specifically to have been bred. This may be accomplished by abdominal palpation and can be done definitively with radiographs. If the dog is not pregnant, false pregnancy is the only other diagnosis consistent with this history and set of physical signs.


Dogs with mild clinical signs are best treated very conservatively. For most, no therapy is necessary and the signs will subside within 7 to 10 days. For dogs with extreme mammary distension that are uncomfortable, I have had good success wrapping the dog’s mammary area with an elastic bandage and cutting the food and water in half for about a day (). This puts pressure on the mammary glands, which sends a signal to the brain to stop secretion of prolactin and subsequent milk production; protects the mammary glands from trauma; and dehydrates the dog a bit, which slows milk production. Do not milk out the engorged mammary glands. Continuous removal of milk from the glands signals the body to continue milk production.

Very aggressive dogs may be treated with sedatives; diazepam (Valium) is the drug of choice. Acepromazine should not be used because it might enhance prolactin secretion and subsequent milk production.

The only medical therapy currently approved for treatment of false pregnancy is the progestogen megestrol acetate (Ovaban). Because the signs of false pregnancy are brought on by a fall in progesterone concentrations in blood, it is logical to assume that those signs can be reversed by administration of progesterone. However, signs often return when therapy is concluded and progesterone concentrations decline again. Androgens (testosterone, mibolerone) have been described as effective for therapy of false pregnancy. Neither drug is approved, nor have they been effective in my experience. Prolactin inhibitors (cabergoline [Dostinex] and bromocrip-tine [Parlodel]) decrease milk production and have been demonstrated as useful for treatment of false pregnancy in bitches. Cabergoline is expensive in the United States and bromocriptine often makes dogs vomit, so use of these drugs is reserved for cases that do not resolve spontaneously within 7 to 10 days.

Ovariohysterectomy (OHE) cannot hasten resolution of clinical signs of false pregnancy in bitches. The clinical signs are due to a lack of progesterone, and removal of the ovaries and uterus will not alter that physiologic state. OHE will prevent future occurrences of false pregnancy because the dog will never go through estrus and diestrus again.


Prognosis is excellent. All dogs go through the hormonal changes of false pregnancy. Those bitches that exhibit clinical signs of false pregnancy are not less fertile than are those that do not show signs of false pregnancy.

Mammary Neoplasia

Test your understanding

You have a 4-year-old bitch that cycles irregularly and has never been bred successfully. On her last breeding, you bred her by natural service 2 and 4 days after a progesterone of 6.6 ng/mL. She tested negative for canine brucellosis before breeding. The male was used to breed another bitch 1 week before yours and that bitch conceived. Your bitch did not conceive but had severe signs of false pregnancy 7 weeks after breeding, with mammary development, lactation, and behavior changes. Is the false pregnancy a sign that she is infertile because of uterine disease?

False pregnancy is not associated with a greater incidence of uterine disease in bitches. The fact that this bitch exhibited signs of false pregnancy shows that she ovu-lated, maintained high concentrations of progesterone, and then had the expected decline in progesterone and rise in prolactin that we will want her to have when she whelps. The cause of her irregular cycling and lack of conception is not known, but they are not due to her false pregnancy.


Selections from the book: “The Dog Breeder’s Guide to Successful Breeding and Health Management”, 2006.