How long does estrus last in rats? - briefly
The estrous phase in rats normally persists for approximately 12–16 hours, after which the animal enters diestrus. This cycle repeats roughly every 4–5 days.
How long does estrus last in rats? - in detail
The estrus phase in laboratory rats occupies only a brief portion of the 4‑ to 5‑day estrous cycle. In most strains, estrus begins shortly after the onset of proestrus and ends within 12–14 hours. In some reports, the interval extends to 18–24 hours, particularly in older or larger females. The precise duration depends on several variables:
- Strain: Sprague‑Dawley and Wistar rats typically display the shorter 12‑hour window; Long‑Evans rats may show up to 18 hours.
- Age: Juvenile females (<8 weeks) often have a slightly prolonged estrus, whereas mature adults (>12 weeks) conform to the 12‑hour norm.
- Photoperiod and housing: Constant light or high‑density cages can shift hormonal timing, occasionally lengthening the estrus period by a few hours.
- Hormonal status: Exogenous administration of gonadotropins or estrogen can artificially extend or shorten the phase.
Researchers determine the timing by daily vaginal smear cytology. The transition to estrus is identified by a predominance of cornified epithelial cells; the return to metestrus is marked by the emergence of leukocytes and nucleated epithelial cells. Sampling every 4–6 hours around the expected transition provides accurate resolution of the phase length.
In summary, the estrus interval in rats is generally 12 hours, with documented ranges of 12–24 hours depending on genetic background, age, and environmental conditions. Precise measurement requires frequent cytological assessment.