Disorders of the Mammary Glands

18 Disorders of the Mammary Glands




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 (see Chapter 8). 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.

Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Disorders of the Mammary Glands

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