A false pregnancy is called a pseudocyesis. It occurs when an unspayed and nonpregnant female dog goes through a phase of breast enlargement, production of milk and behavior similar to that of pregnant bitches. The affected bitch often allows nursing and displays mothering tendencies.
All bitches produce the hormone progesterone for two months after ovulation, which results in mammary gland development. When progesterone decreases abruptly, it stimulates the release of another hormone called prolactin. Prolactin causes mothering behavior and lactation.
A false pregnancy can also occur from the sudden withdrawal of progesterone therapy in an intact bitch or following an ovario-hysterectomy (spay) during the later phases of a female dog’s heat cycle.
Clinical signs of a dog in false pregnancy are breast enlargement and a dilute milk coming from the nipples when lightly squeezed. Common behavioral changes include mothering of inanimate objects in the household, nesting and periods of aggression. Inflammation of the mammary glands may also occur because the breast tissue is enlarged and engorged.
Diagnosis is based on clinical signs in a dog that was in heat approximately two months previously. If there was any chance the dog was bred during its last heat, an abdominal ultrasound is recommended to rule out a true pregnancy.
Most signs of a false pregnancy usually disappear within two to three weeks. Mammary glands should not be milked but left alone. Spaying the dog doesn’t stop the signs of a false pregnancy, but does prevent recurrence. In aggressive females, sedatives may be prescribed.
The age at which pseudocyesis occurs is variable, and does not always occur with every heat cycle. Development of a false pregnancy usually means normal ovarian function and does not usually indicate any uterine disease. Multiple episodes of false pregnancies may predispose a dog to malignant mammary tumors in her later years.
Dr. Karsten Fostvedt is a veterinarian at St. Francis Pet Clinic in Ketchum.