Anestrus

Anestrus is a period of rest during which the sexual organs remain practically inactive and is a characteristic both of wild and tamed dogs. However, the duration period varies according to each individual dog. In general terms, an estrus lasts between 5 and 5 1/2 months, which represents a complete cycle of approximately 8 months; or another way of putting it would be three complete estrus cycles every two years, although there are cycles that can last up to 14 months and are considered normal. In fact there are some breeds, for example the Basenji, which only has one yearly heat period (the same as with wild dogs, wolves, jackals and foxes), usually at the end of winter or Tibetan Mastiffs which only have one yearly heat period in the months of fall.

Recent investigations have determined that, in spite of what was once believed, there is no such thing as a total hormonal inactivity during the stage of anestrus; instead, in fact, the pituitary gland and the ovaries themselves continue with a certain activity, although the final unleashing factor of the anestrus stage and beginning of the proestrus stage is unknown.