Difference Between Estrous and Menstrual Cycle

The key difference between estrous and menstrual cycle is that estrous cycle is the reproductive cycle of females of non-primate mammals in which the endometrium is reabsorbed by the walls of the uterus while menstrual cycle is the reproductive cycle of females of primate mammals in which endometrium is shed via bleeding.

Estrous and menstrual cycle are two types of cycles that occur in female mammals. Both cycles begin after sexual maturity in females. Reproductive hormones induce these cycles in females. These cycles happen in order to prepare female mammals for holding a child during pregnancy. Oestrous cycle occurs in non-primates such as cows, sheep, horse, rabbit, and pig, etc. The menstrual cycle occurs in primates such as monkeys, apes and humans, etc.  Endometrium is reabsorbed in the estrous cycle while it is shed in the menstrual cycle.

CONTENTS

1. Overview and Key Difference
2. What is Estrous Cycle
3. What is Menstrual Cycle
4. Similarities Between Estrous and Menstrual Cycle
5. Side by Side Comparison – Estrous vs Menstrual Cycle in Tabular Form
6. Summary

What is Estrous Cycle?

Estrous cycle is the reproductive cycle of females of non-primate mammals. Therefore, estrous cycle occurs in females of non-primates such as cows, domestic pigs,  sheep, goats, deer, elk, horses, hamsters, ferrets, canines, dioestrous, bears, foxes, and wolves, etc. The endometrium is reabsorbed by the walls of the uterus in these animals. Therefore, bleeding does not happen during the estrous cycle.

Generally, the estrous cycle repeats after 21 days. Female animals are sexually active only during the estrus phase of the cycle. Estrous cycle is less complex than the menstrual cycle. It has four short phases: proestrus, estrus, metestrus and diestrus.

What is Menstrual Cycle?

The menstrual cycle is the reproductive cycle of females of primates, especially in humans. Generally, it repeats after every 28 days. Furthermore, the menstrual cycle starts after sexual maturity (at puberty) and continues till menopause. There are three major phases of the menstrual cycle. They are menstrual, proliferative (follicular), and secretory (luteal) phases. Ovulation occurs in the ovulatory phase. It happens between the proliferative and secretory phases. Reproductive hormones induce the menstrual cycle.

There is a high estrogen level in the proliferative phase. Moreover, there is a high progesterone level in the secretory phase. Females of primates are sexually active at any time of the menstrual cycle. During the menstrual period, the endometrium is shed in primates.

What are the Similarities Between Estrous and Menstrual Cycle?

• Estrous and menstrual cycles take place in mammals.
• Both cycles start after sexual maturity in females and continue till menopause.
• These cycles are driven by reproductive hormones in females.
• They prepare female mammals for holding a child during pregnancy.
• Both cycles give females of mammals repeated opportunities to become pregnant throughout their productive lifetime.

What is the Difference Between Estrous and Menstrual Cycle?

Estrous cycle refers to the reproductive cycle of females of non-primate mammals. Whereas, menstrual cycle refers to the reproductive cycle of females of primate mammals. So, this is the key difference between estrous and menstrual cycle. Another major difference between estrous and menstrual cycle is that the endometrium is reabsorbed during the estrous cycle while the endometrium is shed during the menstrual cycle.

The below infographic summarizes the difference between estrous and menstrual cycle in tabular form.

Summary – Estrous vs Menstrual Cycle

Estrous and menstrual cycle are two reproductive cycles occurring in female mammals. They show cyclic ovarian functions. Estrous cycle occurs in non-primate mammals while the menstrual cycle occurs in primates. So, this is the key difference between estrous and menstrual cycle. Another major difference between estrous and menstrual cycle is that during the estrous cycle, the endometrium is reabsorbed while during the menstrual cycle, the endometrium is shed via bleeding.

Reference:

1. “Estrous Cycle.” Embryology, Available here.
2. “Menstrual Cycle Tool.” Womenshealth.gov, 16 Mar. 2018, Available here.

Image Courtesy:

1. “Anatomy and physiology of animals The oestrous cycle” – The original uploader was Sunshineconnelly at English Wikibooks. – Transferred from en.wikibooks to Commons by Adrignola using CommonsHelper. (CC BY 3.0) via Commons Wikimedia
2. “MenstrualCycle2 en” By Isometrik – Own work (CC BY-SA 3.0) via Commons Wikimedia