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Boy or girl: tips to determine the sex of your small pet

Boy or girl: tips to determine the sex of your small pet 


Identifying the sex of a small pet is often more difficult than identifying the sex of a dog or cat. It’s extremely important to get it right though – incorrectly sexing your small pets could mean you end up with an accidental pregnancy. That might not sound so bad, until you consider that you will then be left with the responsibility of finding suitable homes for all the offspring and will have to set up at least one other cage to prevent the males and females from mating again. It is far better to make sure you have determined the sex of your small pets correctly from the beginning – if you are in doubt about whether you have sexed each one correctly we suggest you visit your vet for confirmation.


Guinea pigs

Guinea pigs are born almost fully developed, but we recommend sexing at least 2 weeks after birth, to leave less opportunity for errors.

Female: A ‘Y’- shaped opening will appear when parting the genital opening  

Male: Applying slight pressure to the area above the genital opening should cause the penis to protrude outwards. 


Rats & Mice


Rats also mature very early, and are fully developed by 5 weeks of age. From this time onwards the difference between males and females should be quite easy to spot.




It can be hard to sex hamsters.  Male hamsters, have rounder bottoms and the distance between the penis and anus is greater than in the female.                                                                                                                                                   

The female has nipples and the distance between the genital opening and anus is extremely small, on dwarf hamsters it can look like one hole.


Applying pressure to the genital area, you can determine the sex of your rabbit. The easiest way to do this is to hold the rabbit on its back, with it’s hind legs facing away from you. 

In females, the vulva will often protrude when pressure is applied, and appears more pyramid shaped and slanted in appearance compared to the male.

In males, the testicles can be seen by parting the fur away around the genital area. Applying pressure around the genital area will cause the penis to pop out.  If the penis does not protrude a tube with an opening will appear.


Correctly determining the sex of your Ferret is even more important than in the other species we have mentioned. Females are induced ovulators, like cats. This means that once they come into season they will stay in season unless mated by a male. The persistently high levels of oestrogen that result from this can lead to aplastic anaemia, a life threatening condition in which the bone marrow stops producing all types of blood cells. This means that if you have only 1 female ferret, or 2 females, then it is important that you arrange to have them speyed before they come into season for the first time. Fortunately, determining the sex of a ferret is usually quite straightforward.

Male ferrets have obvious external testicles, which clearly distinguishes them from females.

Female ferrets’ vagina can appear swollen when in heat, as in this picture. Otherwise the lack of testicles is a sure sign of your ferret being a female.