- Examine anogenital distance to determine gender in neonatal rodents and in chinchillas of all ages. The distance between the anus and the urogenital region is relatively short in female rodents and longer in males.
- Sexing can be challenging in chinchillas since the clitoris and penis morphology appear quite similar, however the anogenital distance is approximately twice as long in males.
- Use external anatomy to sex adult hedgehogs, sugar gliders, ferrets, rabbits as well as rodents such as the guinea pig, rat, and hamster.
- The testicles may be retracted into the abdomen of the adult rabbit as well as many species of rodents.
- Mature males are often larger than females, except in chinchillas where the females are generally larger.
External reproductive anatomy is obvious in some adult small mammals such as the ferret, sugar glider, hedgehog, rat, guinea pig, and hamster. Gender determination or sexing can be challenging in some species like the chinchilla, and in many neonatal rodents. In these cases, reliance on anogenital distance or the distance between the rectum and the urogenital region is considered best practice. The anogenital distance is relatively short in females and longer in males.
To sex a rabbit (Oryctolagus cuniculus), apply gentle pressure to the genitalia. A bullet-shaped penis will evert in bucks (Fig 1), while the vulva in does has a more slit-like appearance (Fig 2). Male rabbits also have a hairless scrotum that sits cranial to the penis. Open inguinal rings allow the testicles to be retracted into the abdomen. Bucks do not have an os penis or nipples.
Females of some breeds normally have a dewlap, a flap of skin that hangs beneath the chin (Fig 3).
Anogenital distance is longer in male rodents (Fig 4). Rodents also have an open inguinal ring and most species can retract the testes into the abdomen. An os penis or baculum is present in hamsters, gerbils, rats, guinea pigs (Cavia porcellus), chinchillas (Chinchilla lanigera) and mice.
Sexing can be challenging in chinchillas since the clitoris and penis appear quite similar, however the anogenital distance is about twice as long in males (Fig 5). Male chinchillas lack a true scrotum and the testicles sit within the inguinal canal instead. Both genders have one pair of inguinal mammary glands and two pairs of lateral thoracic mammary glands. Female chinchillas are usually larger. See Lowcountry Chinchillas and Meadowbrook Chinchillas for images illustrating male and female chinchilla external genitalia.
Both the prepuce in male degus (Octodon degus) and the clitoris in females are located ventral to the anus, but the prepuce is considerably larger. The male also lacks a scrotum. Intra-abdominal testicles sit within two separate hemiscrotal sacs. Females have four pairs of mammary glands.
Male Mongolian gerbils (Meriones unguiculatus) are larger, with darkly pigmented scrotum, and more prominent marking glands on the flanks. The male also has a prominent genital papilla. This papilla is less pronounced in females, and female gerbils also have nipples.
The penis can be everted from the prepuce using gentle digital pressure on the boar’s genitalia (Fig 6). Sows have a Y-shaped vaginal closure membrane between the anus and the urethra. The vulva is at the junction of the “Y” (Fig 7).
The scrotum creates an obvious bulge giving the rear of the male hamster a rounded appearance. The female has a relatively blunt rear and 6 pairs of nipples. Male hamsters are also relatively large when compared to females.
As in other rodent species, anogenital distance is longer in male mice (Fig 8). Male mice (Mus musculus) have a prominent scrotal sac. Males are also typically twice the size of females. The presence of nipples is also an indication of female gender.
A distinct scrotum is located between the anus and prepuce in the male rat (Fig 10). Only female rats have nipples (Fig 11).
Ferrets, sugar gliders, and hedgehogs
The prepuce of the male ferret (Mustela putorious furo) or hob sits on the ventral mid-abdomen, and the os penis is easily palpable. Although many American ferrets are neutered before sale, the testicles may be located cranioventral to the anus. Males are also typically larger, while jills are relatively small and petite.
Male sugar gliders (Petaurus breviceps) have a pendulous scrotum, and a forked penis sits behind the scrotum. Males also possess a ventral chest gland as well as a scent gland on top of the head.
Male African hedgehogs (Atelerix albiventris) have a relatively long anogenital distance. The prepuce sits midway along the ventral abdomen. Hedgehogs lack a scrotum but the testicles are palpable within subcutaneous tissues. As in rodents, the anogenital distance is short in female hedgehogs and the vulva is located close to the anus. A vaginal plug is present after mating in female hedgehogs.
Although external reproductive anatomy is fairly obvious in some adult exotic companion mammals, gender determination or sexing can be challenging in some species like the chinchilla, and in many neonatal rodents. In these cases, examine anogenital distance to determine gender. The distance between the anus and the urogenital region is relatively short in female rodents and longer in males. Sexing can be challenging in chinchillas since the clitoris and penis morphology appear quite similar, however the anogenital distance is approximately twice as long in males.