How does rat pregnancy occur? - briefly
After copulation, sperm ascend the female reproductive tract and fertilize ova in the oviducts; the resulting embryos implant in the «uterine» lining approximately four to five days later. Gestation lasts about 21–23 days, after which the litter is born.
How does rat pregnancy occur? - in detail
The reproductive cycle of laboratory rats consists of a short estrous phase that repeats every four to five days. During the proestrus and estrus stages, the female exhibits sexual receptivity, and ovulation occurs spontaneously at the end of estrus without external stimulus.
Mating takes place when a male mounts a receptive female, deposits a sperm‑rich ejaculate, and triggers a neuroendocrine reflex that facilitates uterine contractions. Sperm travel through the cervix, uterus, and oviducts, reaching the ovulated oocyte within minutes. Fertilization occurs in the ampulla of the oviduct, where a single sperm penetrates the zona pellucida and fuses with the oocyte membrane, forming a zygote.
The zygote undergoes rapid mitotic divisions as it moves toward the uterine lumen. By day three post‑coitus, the morula reaches the uterine cavity and initiates implantation. Attachment to the endometrial epithelium involves trophoblast invasion and formation of a placenta that will sustain nutrient exchange throughout gestation.
Gestation in rats lasts approximately twenty‑three days. Key developmental milestones include:
- Day 4–5: Formation of the embryonic disc and onset of gastrulation.
- Day 7–9: Development of the neural tube and early organ primordia.
- Day 12–14: Differentiation of limb buds and visible fetal movement.
- Day 18–20: Maturation of the respiratory and circulatory systems.
- Day 22–23: Preparation for parturition, including lung surfactant production.
Hormonal regulation is driven primarily by estrogen, progesterone, prolactin, and luteinizing hormone. Estrogen peaks during estrus to induce sexual behavior, while progesterone, produced by the corpus luteum, maintains uterine quiescence and supports implantation. Prolactin sustains luteal function throughout pregnancy, and a gradual decline in progesterone near term triggers uterine contractility.
Litter size averages six to twelve pups, varying with strain, age, and nutritional status. Parturition commences with cervical dilation, followed by the sequential delivery of pups, each accompanied by a brief period of uterine contraction. Post‑natal maternal behavior includes pup retrieval, grooming, and initiation of lactation, completing the reproductive cycle.