How to determine a rat's sex? - briefly
Inspect the ventral area just behind the anus; males display a scrotum and a noticeably longer anogenital distance, while females show a small vulvar opening with a shorter distance. This visual comparison reliably distinguishes the sexes.
How to determine a rat's sex? - in detail
Identifying a rat’s gender requires careful observation of the external genital region. The procedure differs between juveniles and adults because the anatomical landmarks develop with age.
In adult specimens the ventral surface of the tail base displays a clear separation between the anus and the genital opening. Males possess a single, circular opening (the urethral orifice) situated directly caudal to the anus, with a visible scrotal sac containing two testes beneath the skin. The testes may be palpable as firm, oval structures when the animal is warm‑blooded. Females have a single, slit‑like opening (the vaginal orifice) situated slightly ventral to the anus, and no scrotal tissue is present. The external genitalia form a short, rounded “Y” shape, often referred to as the “vulvar lips,” which can be seen when the fur is gently part‑removed.
Juvenile rats (under three weeks old) lack fully developed testes and scrotal sacs, making visual differentiation more challenging. The following steps improve accuracy:
- Restrain the animal using a gentle grip on the tail and hind limbs, minimizing stress.
- Part the fur around the anus and genital area with fine forceps or a blunt needle, exposing the skin.
- Locate the anal opening; it appears as a dark circular pore.
- Examine the region immediately posterior to the anus:
- Confirm by palpation: gently press the area behind the opening. In males, a firm mass (developing testes) may be felt; in females, the tissue feels uniformly soft.
When visual cues remain ambiguous, especially in neonates, a brief examination under a dissecting microscope can reveal the presence of the pre‑putial gland in males or the absence of it in females. This method should be performed with sterile instruments and proper ethical oversight.
Proper lighting, a clean work surface, and minimal handling time reduce the risk of injury and stress. Recording the observed characteristics for each animal ensures consistent documentation and facilitates future breeding or research protocols.