How do a female rat and a male rat look? - briefly
Female rats are generally larger, with a broader pelvis and without the conspicuous anogenital swelling that characterizes males. Male rats display a visible scrotum and a pronounced anogenital ridge.
How do a female rat and a male rat look? - in detail
Female rats are typically slightly larger than males of the same age, with a broader, more rounded abdomen that accommodates reproductive organs. Their overall body length, from nose to base of tail, averages 9–10 cm, while males range 8–9 cm. Both sexes possess smooth, hairless skin on the ventral surface, but females display a more pronounced pelvic widening, visible as a subtle flare of the hindquarters.
The tail of a female is uniformly thin along its length, ending in a rounded tip. In contrast, a male’s tail often shows a slight thickening near the base, reflecting the presence of the scrotal sac underneath. The scrotum is external, covered by a thin, wrinkled layer of skin, and becomes more evident after sexual maturity (approximately 6–8 weeks). It contains two testes that can be palpated as firm, oval masses.
Fur coloration and texture are identical between the sexes; common laboratory strains exhibit a grayish‑brown dorsal coat and a lighter ventral side. The dorsal hair is dense and coarse, while the ventral hair is finer. Neither sex shows distinct markings that differentiate them.
External genitalia provide the clearest visual cues:
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Female:
- Vulva located just behind the anus, appearing as a small, slit‑like opening.
- Absence of a scrotal pouch.
- Mammary nipples (typically eight) aligned in two parallel rows along the ventral abdomen; nipples are more prominent in lactating females.
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Male:
- Prepuce covering the penis, visible as a small, recessed opening.
- Prominent scrotum with visible testes.
- Absence of prominent nipples; only rudimentary mammary buds may be present.
These anatomical features allow reliable sex identification in both live and post‑mortem specimens without reliance on behavioral observations.