Do cats menstruate?

Menstruation is the shedding of the endometrium or the uterine lining. This period that is characterized by vaginal bleeding occurs regularly in females of some placental mammal species. Females in the sexually reproductive age would menstruate monthly unless pregnancy occurs. Cats are placental mammals. Female cats go through reproductive cycles but unlike pigs, dogs and other domestic animals, cats do not menstruate.

In humans, menstruation is also known as period. Menstruation that is mainly characterized by vaginal bleeding starts at the age of puberty and ends at menopause. While in the sexually reproductive age, the body of human females would prepare for possible pregnancy. The lining of the uterus is thickened with blood rich tissues. But if the egg is not fertilized and pregnancy did not occur, the uterine lining will have to be shed. Menstrual fluid that will be shed through the vagina contains blood mixed with vaginal secretions, cervical mucus and pieces of the uterine lining. Cats, just like other placental mammals go through reproductive cycle. In cats, the fertile period is called estrus, in heat or “calling” or being “in season”. The fertile period of cats is the same as the menstrual period in humans. The cat’s body would go through the same preparation for a possible pregnancy. The only difference is that in cats there will be no vaginal bleeding.

The age when cats attain sexual maturity differs in individuals but generally, a cat would come into its first heat cycle at the age of six months. Cats are polyestrus meaning, they go into heat repeatedly during the breeding season. In dogs, the estrus cycle occur approximately every six months. Human female’s period will occur monthly during which an egg will be produced for fertilization. This is not so with cats as these animals would be in heat for about 4 to 10 days. If pregnancy did not occur, the cat will go in and out of the estrus cycle during the entire breeding season. A cat in heat would manifest dramatic behavioral changes. The cat would become more affectionate. The estrus cycle is also called calling because during this period the cat tends to vocalize excessively. This is the cat’s way of attracting potential sexual partner. An indoor cat that has no access to a potential mate would take on the mating position. The chest and the forelegs will be down on the ground while the hind legs are stretched to elevate the rump.

Cats are induced ovulators. Unlike other mammals that release an egg for fertilization every estrus cycle, cats’ ovaries will only release a ripened egg if the cat was mated. It will be noticed that cats have a very gets very noisy during copulation. The withdrawal of the spiked penis of the male cat that causes the female cat to scream also triggers ovulation. Just like other mammals, cats too prepare for a possible pregnancy by thickening the uterine walls with blood vessel rich tissue. However, unlike other mammals, cats would expel the endometrium from the uterus if pregnancy does not occur. Cats do not menstruate because these animals reabsorb the endometrial lining. Cats are one of the placental mammals that clean the uterus by absorbing the uterine lining. This is the reason why cats do not have vaginal bleeding at the end of every estrus cycle. Given the small size of the cat’s uterus, it is expected that the cervical mucus, the vaginal secretions and the thickened uterine lining would not be of sizeable amount and therefore can be easily absorbed by the body. Additionally, cats would be benefited from this kind of set up. The absorption of the blood-rich tissue would aid in the maintenance of the cat’s health.