How can I determine the sex of a rat pup? - briefly
Examine the anogenital area: males display a scrotal sac and a greater distance between the anus and the genital papilla, whereas females have a single, rounded opening situated close to the anus.
How can I determine the sex of a rat pup? - in detail
Determining the gender of a newborn rat requires careful visual examination of the external genital region. The most reliable results are obtained when the animal is between 10 and 14 days old; at this stage the anogenital distance is evident and the fur has not yet fully covered the area.
To assess sex, follow these steps:
- Gently restrain the pup by holding the base of the tail with one hand while supporting the body with the other.
- Position the animal on a clean, well‑lit surface. Use a magnifying lens if available.
- Locate the opening of the anus; it appears as a small circular slit.
- Measure the distance from the anus to the genital opening (anogenital distance). In males this gap is roughly twice that of females.
- Examine the genital opening itself. In males, a small, rounded structure (the preputial gland) and, later, visible testes develop in the scrotal area. In females, the opening is a simple slit leading to the vulva, with no protruding structures.
- Record observations and, if needed, repeat the check after 24 hours to confirm development.
When visual cues are ambiguous, molecular techniques provide confirmation. A small tissue sample (e.g., tail tip) can be subjected to PCR targeting the Sry gene, which is present only in males. This method is accurate but requires laboratory equipment and ethical approval.
Common pitfalls include:
- Assessing sex immediately after birth; the anogenital distance is minimal and can lead to misidentification.
- Mistaking the perineal skin fold for the genital opening, especially in pigmented or hair‑dense pups.
- Over‑handling, which may stress the animal and affect development.
By adhering to the described protocol and timing, sex identification can be performed quickly, accurately, and with minimal disturbance to the colony.