How do rats look at different ages? - briefly
Newborn rats are hairless, pink, and have closed eyelids; by the third week they acquire a full fur coat, open eyes, and a larger body proportion. Adult individuals display dense fur, fully developed whiskers, and clear sexual dimorphism in size and genitalia.
How do rats look at different ages? - in detail
Rats undergo distinct morphological changes from birth to senescence.
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Newborn (post‑natal day 0‑4): hairless, pink skin; eyes sealed, ears flat against the head; body length 5–7 cm, weight 5–7 g. Umbilical scar visible.
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Early neonate (day 5‑10): fur begins to appear, initially sparse and gray‑white; eyes open around day 14; ear pinnae lift slightly; weight rises to 12–15 g.
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Weanling (day 21‑28): full coat of soft fur, typically brown or black depending on strain; ears fully erect; tail length approximates body length; weight 40–60 g; dentition includes erupting incisors.
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Adolescent (day 35‑60): coat thickens, becomes glossy; musculature increases, especially in forelimbs; sexual dimorphism emerges—males develop larger testes, broader heads; weight 120–200 g; skeletal growth plate closure begins.
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Adult (day 90‑180): stable coat coloration, dense guard hairs; tail proportion unchanged; body mass 250–350 g for common laboratory strains; reproductive organs fully mature; skeletal growth completed, epiphyses fused.
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Aged (≥ 18 months): coat may lose luster, exhibit thinning or graying; skin becomes less elastic, occasional alopecia patches; body weight may decline or remain stable depending on health; muscle mass decreases, leading to a sagging appearance; tail may show reduced flexibility.
These stages reflect predictable physical markers that researchers use to age‑classify rats in experimental settings.