Dogs have an estrus cycle 1-2 times a year. The ovaries release eggs (ova) and the remaining area forms the corpus luteum. This hormone-producing structure will help maintain a pregnancy if the animal is bred. If pregnancy does not occur, the corpus luteum will regress and stop producing the hormone progesterone, a hormone necessary for pregnancy.
In animals that experience pseudopregnancy, the corpus luteum does not regress as expected and continues to produce progesterone. This results in signs seen that are common in late pregnancy: nesting behavior, territoriality, mothering behavior (collecting toys, etc.) as well as mammary gland development and milk production.
It is important to note that if you dog seems lethargic or sick to have her examined by your veterinarian. Another post-estrus condition that may be seen is pyometra, a potentially life-threatening condition. This is in contrast to pseudopregnancy, which is usually a benign, self-resolving condition.
Most signs seen with pseudopregnancy will go away on their own in 2-3 weeks. While the dog may be a little uncomfortable, it is important not to stimulate the mammary glands (for example, warm compress), as this may also stimulate more milk production.
Spaying will correct this condition, but should be done after the hormones have cycled down naturally, otherwise the pseudopregnancy may be prolonged. This is because production of the hormone prolactin in the pituitary gland keeps going even after the ovaries are removed.