Metestrus

Metestrus is a term used in the physiology of the estrous cycle in many non-primate mammals. It denotes the interval that follows ovulation (estrus) and precedes diestrus, during which the corpus luteum forms and begins secreting progesterone. The phase marks the early luteal period of the cycle in species such as rodents, cows, and pigs.

Hormonal and tissue changes underpin metestrus. After the follicle ovulates, it transforms into the corpus luteum, leading to rising progesterone levels and a shift in the endometrium toward secretory changes. Estrogen levels typically decline from the high levels seen in estrus, and the reproductive tract prepares for a potential pregnancy. In humans, the term metestrus is less commonly used; the analogous period after ovulation is generally described as the early luteal or secretory phase.

Clinical and diagnostic notes. In veterinary and research settings, vaginal cytology can aid in identifying metestrus. Smears during this phase may show a mix of cornified epithelial cells along with leukocytes, reflecting the transition from estrus toward diestrus. The exact cellular pattern and duration of metestrus vary by species.

Species variation and terminology. Because the boundaries of estrous cycle phases differ across species, the label metestrus is used with reference to the specific animal. In humans, the term is rarely used in clinical practice, with emphasis instead on the follicular, ovulatory, and luteal phases of the menstrual cycle.