Menstruation (mammal)
Menstruation in mammals is the shedding of the uterine lining (endometrium). It occurs on a regular basis in uninseminated sexually reproductive-age females of certain mammal species.
Menstruation (mammal)
Females of other species of placental mammal undergo estrous cycles, in which the endometrium is completely reabsorbed by the animal (covert menstruation) at the end of its reproductive cycle. Many zoologists regard this as different from a "true" menstrual cycle. Female domestic animals used for breeding —for example dogs, pigs, cattle, or horses— are monitored for physical signs of an estrous cycle period, which indicates that the animal is ready for insemination.