Anovulatory cycle
While the normal menstrual cycle in the human typically lasts 4 weeks (28 days, range 24–35 days) and consists of a follicular phase, ovulation, and a luteal phase, followed by either menstruation or pregnancy, the anovulatory cycle has cycle
lengths of varying degrees. In many circumstances, menstrual intervals are prolonged exceeding 35 days leading to oligomenorrhea (cycle >35 – 180 days interval), or even longer, amenorrhea. In other cases, menstruation may be fairly regular (eumenorrhea), or more frequent (intervals < 21 days), or there may be a loss of menstrual pattern (menorrhagia, dysfunctional uterine bleeding).
Dog behavior
Female dogs have an estrous cycle that is nonseasonal and monestrus, i.e. there is only one estrus per estrous cycle. The interval between one estrus and another is, on average, seven months, however, this may range between 4 and 12 months. This interestrous period is not influenced by the photoperiod or pregnancy. The average duration of estrus is 9 days with spontaneous ovulation usually about 3 days after the onset of estrus.