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).
Nyala
Before ovulation, the Graafian follicles reach a length of at least . A female's estrus cycle is about 19 days long. Males mate with the female for two days of the cycle, but she allows it for only six hours per cycle. When the male enters a females' herd during mating, he makes a display by raising his white dorsal crest, lowering his horns and moving stiffly. As in many other animals, the males fight over dominance during mating.