"Female" - what is it, definition of the term
In rodent biology, the term designates the biological sex characterized by XX chromosomes, development of mammary tissue, and the capacity to generate ova; individuals of this sex bear young after a gestation of roughly 21–23 days in rats and 19–21 days in mice, possess ovaries and a uterus, and typically exhibit smaller body size and distinct reproductive anatomy compared with their counterpart.
Detailed information
Rats and mice belonging to the oviproducing sex exhibit distinct anatomical and physiological traits that differentiate them from their male counterparts. The reproductive system includes paired ovaries, oviducts, a uterus, and a well-developed mammary gland network. Hormonal regulation follows a cyclical pattern driven primarily by estrogen and progesterone, which orchestrate follicular development, ovulation, and preparation of the uterine lining for implantation.
The estrous cycle in these rodents is notably brief. A complete sequence lasts approximately four to five days, with the following phases:
- Proestrus: rapid follicular growth, rising estrogen levels.
- Estrus: ovulation occurs, lasting 12–14 hours; females are receptive to mating.
- Metestrus: corpus luteum formation, progesterone increase.
- Diestrus: uterine quiescence, preparation for potential pregnancy.
Mating behavior is initiated during estrus, when scent cues and ultrasonic vocalizations signal readiness. After successful copulation, fertilization typically occurs within the oviducts, and implantation follows within 4–5 days. Gestation periods are species‑specific: approximately 21–23 days for rats and 19–21 days for mice. Litter sizes average 8–12 offspring for rats and 5–8 for mice, with each neonate receiving nourishment through well‑developed mammary glands that transition from colostrum production to mature milk within a few days postpartum.
Maternal care is intensive. Dams construct nests from shredded paper or bedding, maintain a stable microclimate, and exhibit pup‑retrieval behavior when offspring are displaced. Pup mortality is lowest when the dam remains undisturbed, as stress can trigger cannibalism or neglect. Lactation peaks around day 10 postpartum, after which weaning typically occurs at 21 days for rats and 18 days for mice.
Physiological differences extend to metabolism. The oviproducing sex displays higher basal body temperature and altered glucose handling, reflecting the energetic demands of gestation and lactation. These metabolic shifts are mediated by increased leptin and insulin sensitivity, which support fetal growth and milk synthesis.
In laboratory settings, identification of the oviproducing sex relies on visual markers such as anogenital distance, nipple development, and, when necessary, genetic testing for sex‑determining chromosomes. Accurate classification is essential for experimental design, particularly in studies involving reproductive toxicology, endocrinology, and behavioral neuroscience.