False pregnancy is common in bitches and uncommon in queens. It occurs at the end of diestrus and is characterized by hyperplasia of the mammary glands, lactation, and behavioral changes. Some bitches behave as if parturition has occurred, “mothering” by nesting inanimate objects and refusing to eat. The possibility of a true pregnancy should be eliminated by the history, abdominal palpation, and abdominal radiographs and ultrasonography.
The falling progesterone and increasing prolactin concentrations associated with late diestrus are believed to be responsible for the clinical signs. No treatment is recommended, because the condition resolves spontaneously in 1–3 wk. In bitches with discomfort secondary to mammary gland enlargement, alternating cold and warm compresses on the engorged mammae or wrapping the abdomen with an elastic bandage may give relief. Owners should be advised not to milk out the mammary glands, because doing so will only stimulate lactogenesis.
Tranquilizers (eg, diazepam, PO, up to 4 days) may be considered for bitches with significant behavioral changes. Estrogens should not be used because of the potential for bone marrow suppression. Megestrol acetate, a progestin (2.5 mg/kg/day, PO, for 8 days), is the only drug currently approved for treatment of false pregnancy in bitches in the USA. Prolonged or repeated use of megestrol acetate may cause pyometra. Androgens (eg, mibolerone, 16 mcg/kg/day, PO, for 5 days) may decrease clinical signs of false pregnancy in bitches. Mibolerone is not approved for treatment of false pregnancy in bitches in the USA. If owners are distressed by repeated bouts of pseudopregnancy, the bitch should either be bred or undergo ovariohysterectomy.