The average length of a female elephant’s estrous cycle is 14 to 16 weeks. There is a four- to six-week follicular phase, when progestagin hormone concentrations are low, and an eight- to ten-week luteal phase, when progestagin hormone concentrations are high.
Elephants are very unusual among mammals because they have two surges of luteinizing hormone (LH) during their follicular phase instead of just one, a fact recently documented by the Zoo's Janine Brown. LH prepares the female's uterus for implantation of a fertilized egg, stimulates ovulation, and stimulates the secretion of progesterone.
The first LH surge, called the anovulatory surge because it does not induce ovulation, occurs roughly two weeks after progesterone concentrations drop, and exactly 21 days before the second LH surge. The second surge does induce ovulation so it is commonly referred to as the ovulatory surge.
The exact function of the first, or anovulatory LH surge, is not yet known, but it may have evolve to let males in the wild know when a female is in estrus, perhaps by changing her odor. The discovery of the double LH surge has been highly valuable in understanding elephant reproduction as well as for breeding them in zoos. The double LH surge has helped to successfully time artificial insemination and natural breeding.