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How Can You Tell a Rat's Gender?

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It isn’t common practice to get pet rats neutered or spayed, apart from medical emergencies. The risks outweigh the benefits, the relative costs are strictly prohibitive, and rats don’t display hormone-related behavioral problems such as those dogs experience. Rats sure will breed, though; so it's crucial to separate the genders; otherwise you’ll end up with far more rats than you bargained for. Males and females have different care needs.

Physical Differences

After they reach the age of about 5 weeks, rats are easier to sex than many other small rodents. The males have obvious genitalia; the females do not. Look at the underside of your rat under the base of the tail. If you can see furry testicles, you have a boy. If you don’t, she’s a girl. Mature male rats often are substantially larger than adult females.

Physical Differences Before 5 Weeks

Baby rats -- kittens -- show some gender differences that are not obvious. Because handing rats this small can be stressful to them and because you don’t really need to know the sex yet, it is advisable to wait for a few weeks. However, if you need to know for some reason, carefully pick up each kitten and examine the underside. By the age of 2 weeks, females will have several dark dots toward the rear -- these are where the teats will be. By the age of 3 weeks, males might have small testicles showing.

Behavioral Differences

Male and female rats show marked differences in behavior, although neither should be problematic. Individuals vary, but essentially females are extremely active, rushing to explore whenever possible, while males are more placid. Males are curious but happy to spend plenty of time relaxing in their hammocks or your lap. Males tend also to be more territorial. While they’ll get on fine with their littermates and other rats they meet early on, they might be aggressive to new ones. For this reason, take your time with the introductions and start off with separate cages, bearing in mind that grumpy old male rats might never make friends with another.


Basic care is much the same for male and female rats, though some nuances exist. Citrus fruits such as oranges and grapefruits can cause kidney problems in the boys but are fine for females to consume. Both genders may suffer from progressive paralysis in old age, but the condition is more common in males. A rat suffering from progressive paralysis requries a single-level cage.


Rats are sociable; keep them in small groups or pairs. These must be single-gender groups to prevent unwanted offspring. Separate genders should before the juveniles are able to reproduce at 5 or 6 weeks. Females can stay with their mother; males need a separate cage. Rats breed quickly and early.

Because male rats tend to be laid back and sedentary, they often don’t burn as many calories as the females, making them more liable to suffer from obesity, which causes all sorts of health problems. For this reason, take special care with their diets and do not provide too many high-calorie treats.