Do all mammals menstruate?
No, very few mammals menstruate. Besides humans, we know that animals who menstruate include simians1 (a subgroup of primates), bats, and the elephant shrew.
However, most female mammals have estrous cycles. Having an estrous cycle means that there are times when it is possible to get pregnant, and times when it is not possible. Some signs of an estrous cycle which may sometimes be mistaken for menstruation. For instance, some animals may have bloody vaginal discharge before they reach their fertile phase. These animals include horses, dogs, and pigs.
- 1. Beverly I. Strassmann , “The Evolution of Endometrial Cycles and Menstruation,” The Quarterly Review of Biology 71, no. 2 (Jun., 1996): 181-220.