Estrous cycle

Overview of the estrous cycle in mammals

Overview

The estrous cycle is a recurring physiological process that occurs in most female mammals, including many domesticated animals. It is the period during which a female is sexually receptive and capable of conceiving. The cycle is characterized by a series of hormonal changes that prepare the body for ovulation and potential pregnancy.

Diagram of the estrous cycle stages.

Phases of the Estrous Cycle

The estrous cycle is divided into several distinct phases:

Proestrus

During the proestrus phase, the body prepares for ovulation. This phase is marked by the growth of follicles in the ovaries and an increase in estrogen levels. The endometrium begins to thicken in preparation for a potential pregnancy.

Estrus

The estrus phase, also known as "heat," is when the female is sexually receptive. Ovulation occurs during this phase, and estrogen levels peak. This is the optimal time for fertilization to occur.

Metestrus

Following estrus, the metestrus phase begins. During this time, the corpus luteum forms from the remnants of the follicle and begins to secrete progesterone. This hormone helps maintain the endometrium and supports early pregnancy if fertilization has occurred.

Diestrus

The diestrus phase is characterized by high levels of progesterone. If pregnancy does not occur, the corpus luteum degenerates, leading to a decrease in progesterone levels and the eventual return to proestrus.

Anestrus

Some species experience an anestrus phase, a period of reproductive inactivity between cycles. This phase can vary in length depending on the species and environmental factors.

Hormonal Regulation

The estrous cycle is regulated by a complex interplay of hormones, primarily gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), estrogen, and progesterone. These hormones are produced by the hypothalamus, pituitary gland, and ovaries.

Species Variations

Different species exhibit variations in the length and characteristics of their estrous cycles. For example, dogs have a cycle that lasts approximately six months, while cows have a cycle of about 21 days. Understanding these differences is crucial for veterinary medicine and animal husbandry.

Related pages

• Menstrual cycle
• Reproductive system
• Ovulation
• Hormonal contraception