Unusual behavior following a heat cycle (estrus) in the non-pregnant female dog is a common occurrence. This condition is termed false pregnancy (hyperluteoidism, pseudocyesis, pseudo-pregnancy). It is a hormonal imbalance and may cause a wide range of clinical signs.
Let’s have a brief review of a normal estrous cycle on the female dog in order to have a better understanding of the abnormal type. The onset of heat is characterized by swelling of the vulva and a bloody discharge which happens from four to fourteen days.
In most female dogs, the bloody discharge lasts about ten days. During this time, the ovaries are preparing eggs for release. As the vaginal discharge changes from bloody to straw color, eggs are expelled from the ovaries. It is during this time that fertilization will take place if she is bred and this period also lasts from four to fourteen days. For most dogs, eggs will be released from the ovaries for ten days.
Following these stages the vulva will gradually return to normal size and the discharges will stop. The areas on the ovaries from which eggs erupted are termed follicles and they will undergo changes to become corpora lutea. These secrete progesterone, a hormone necessary for maintaining a normal pregnancy. If no fertilization occurs, then the corpora lutea will regress in about one month and stop secretion of progesterone.
False pregnancy results when the corpora lutea persist and an excess of progesterone is secreted. This is basically and oversimplification of a complex process but it serves to outline the basic hormonal cause.
Symptoms of False Pregnancy
Clinical signs vary considerably but almost always include increased size of the mammary glands and behavior changes. The onset of false pregnancy will usually fall between one and a half to three months after normal heat cycle.
The mammary glands can be slightly enlarged and produce a thick fluid or they may swell up with actual milk up to the point of discomfort. Behavior changes can range from irritability and aggressiveness to shyness and lethargy. Some dogs want to hide and avoid people while others appear to be actively protecting their phantom litter. Often a toy will be “adopted” and carried almost constantly. Any type of behavior change following a heat cycle should make one suspect of this condition.
Other less common signs are loss of appetite, slight fever, and mild digestive disturbances such as diarrhea. The syndrome can appear from the first heat cycle and usually recurs with every cycle.