So, you’ve decided that pet rats are for you? Now comes the big question – whether to get male or female rats? When it comes down to a preference for girls or boys, some people are strong advocates for a particular sex.
We believe, both male and female rats have their particular strengths and weaknesses, which are best understood from the beginning. To help you make your decision, we will cover the differences and why both sexes can make excellent pets.
How to Tell Whether a Rat Is Male or Female
Many baby rats are still purchased from pet shops, so, let’s begin by making sure we know what to look for when checking the sex of a young rat. Pet shops are notoriously bad at sexing rats – but it’s really not difficult when you know what to look for.
Male juveniles have an external penile nub, then a notable space – which becomes the scrotal sac – before the anus. As male babies mature the testicles descend to fill this space. This happens at around 2 to 4 weeks of age.
A male rat’s testicles are very large for their overall size. They can’t be missed! Despite also having some mammary tissue, males usually don’t have any nipples. In very young infants – before the fur thickens – this is another easy reference point.
Juvenile females have a smaller nub (the urethral opening), which sits just above the vagina. Beyond this, there is a short space before the anus. However, the vagina is closed until around 5 to 6 weeks of age.
Female rats also have two rows of nipples (12 in total) and these are highly visible in the first few weeks of life. In some rats, they remain visible even once the rat is an adult.
In a few instances, a male may only have one (or neither) testicle descend into the scrotal sac. It’s also possible for a rat to have ambiguous sex organs, or even be a true hermaphrodite – being both male and female at the same time.
Juveniles can, in theory, mate from around 5 weeks, so all litters should be separated into males and females before this age.
As well as the differences in sex organs, male and female rats generally differ in body size and type. Adult pet rats are generally larger than wild or laboratory strains, especially where they bred thoughtfully within the rat fancy.
Even pet rats can differ significantly in size and weight depending on their breeding, selection, and nutrition. Most sources suggest around 9 to 11 inches body length with the tail being up to 9 inches long.
Adult males generally weigh between 300 and 800g and females 250 to 500g, but some fancy rats are even bigger than this! Even so, we can see the variation is huge.
The rat has a general standard, recorded for making comparisons at rat shows, regardless of their variety. It outlines their physical characteristics, noting gender differences:
“The Rat shall be of good size, does long and racy type, bucks being of a bigger build, arched over the loin, firm-fleshed with a clean, long head, but not too pointed at the nose. The eyes shall be round, bold, clean and of good size.
The ears shall be of good size, well-formed and widely spaced. The tail shall be cylindrical and as long as the body, thick at the base, tapering to a fine point. The ears, feet, and tail shall be covered with fine hair. The coat shall be smooth and glossy (except for the Rex type). Bucks are larger than does and have a harsher coat.” – NFRS Standards of Excellence, General Conformation.
So in general terms, males are larger, broader, and heavier, with a thicker tail and a coarser coat. They have broad heads and shoulders, often being described as “brick-like” from above.
Females are ‘racy’ – meaning narrower and more streamlined – with a shorter, shinier coat. They tend to be smaller and lighter too, but a small boy can be significantly smaller than a large girl.
Female rats hit puberty around 34 to 38 days old and they continue through until menopause with a 4 to 6-day heat cycle. Menopause occurs between 15 and 18 months, though some females remain fertile into old age.
Rats do not bleed as a result of their heat cycle, and any vaginal bleeding should be considered abnormal. Causes include infection, cystic ovaries, and cancer.
Males reach puberty slightly later – 39 to 47 days, and are constantly able to reproduce right through to old age. They do not have any kind of reproductive cycle, but their testosterone levels do fluctuate a great deal.
Differences in testosterone between individuals can be vast, with one rat having as much as 20x more than another rat circulating in their bloodstream.
Variations within each individual are also significant with wide changes in blood levels over the course of a single day. It is not known what causes these pulses of the hormone.
Fluctuations in sex hormones will certainly have some effect on the behavior of rats of both sexes in terms of social interactions, aggression, and hierarchy. Where this causes problems, castration, spay, and chemical castration can all help.
Sex hormones are also related to the slightly musky smell that many males have (not heavy or unpleasant), and an orange greasy substance, called buck grease, which can be seen in some males at skin level over their rump.
In contrast, humans often describe their female rats as smelling of grapes, perfume, or even popcorn! This is the smell of the actual rat themselves, not their cage – which is more likely to smell of urine or feces!
Male rats are often said to be lazy while females are supposed to be active and interesting. Just stop for a minute and think about how that would work out in the wild!
Activity is not determined by sex, but by environment and expectation. Where bucks are given wheels, open and active cage set-ups, and plenty of opportunities to explore, they can be just as active and interesting as girls.
Bucks may never be as quick and agile, especially where their breeding had pushed their weight up towards 700+ grams, but they can be just as inquisitive and keen to explore.
Male rats often settle into human handling (cuddles and scritches) more easily than females who tend to come to this later in life. Most female rats prefer to be moving rather than sitting still – but there are many boys who share this trait.
Boys can certainly be calm and chilled out – but that doesn’t make them lazy. With lots of handling from birth, almost all rats will enjoy time with their humans and the touch that we often want to share with them.
Female hormonal cycles can – on occasion – affect their behavior, making them more unsettled and even irritable at times. However, many girls show almost no signs of coming into heat and remain cheerful regardless.
All rats have the potential to take part in activities and training, though (through misconception) pet owners often select females to work with, in this regard.
Interestingly, the opposite is true in laboratory studies, where males are often considered the easiest and most consistent to work with! All rats are capable, given the opportunity.
Rats are individuals and their approach to social connections is as varied as our own. Within their hierarchies, they not only need to find their own place and position, but they will show preferences for some rats over others.
Male rats often bond more dependently, particularly with a paired sibling, but they are also harder to introduce to unknown (unrelated) males as adults. Castration can help in some circumstances.
Female rats often seem to have more fluid relationships, and they are generally easier to introduce as adults. But almost all rats form strong social bonds with cagemates, as well as with their humans.
Both males and females (and especially those who are high ranking in their cage group hierarchy) will urine mark as they move through their range. They will mark objects, people and other rats. This involves leaving a droplet of urine as they pass over something.
It has been stated that males do this more than females, but this is not backed up by research, which has found an equal likelihood of both sexes marking.
Many illnesses affect male and female rats equally, but females are much more prone to mammary and pituitary tumors, and also get diseases that affect their uterus and ovaries.
Bucks can get mammary and pituitary tumors too – but these occur much less often in the male. They are, however, more prone to kidney failure and the hind leg weakness that accompanies it.
In relation to their predisposition to kidney issues as they age, male rats have a greater need for a low protein diet from puberty onwards, and a slow growth into adulthood. Adlib feeding affects bucks – and their kidneys – more than does.
All male rats should be fed a low phosphorus, low protein diet as they age and the presumption should be that kidney disease is present well before signs of this begin to show. Rats lose about 70% of kidney function before they get symptoms.
Bucks also have a male-specific protein that binds with the d-limonene in citrus oil causing protein clumps. D-limonene is found in foods like citrus fruits, mango, and herbs such as lemon balm.
The protein clumps build up in the renal tubules and can even progress to kidney cancer. D-limonene does not affect females, who are also more tolerant of higher protein levels in their diet.
The topic of sex-related lifespan differences has been the topic of many laboratory studies and most have found that female rats live longer, especially in groups that are fed adlib (constant food available) throughout their lives.
This is thought to be because of the negative impact of adlib feeding on the natural decline in kidney function that affects male rats in particular. Adlib feeding can significantly increase the rate of decline.
However, even without this dietary influence, female rats will outlive male rats by 2 to 15% on average lifespan.
We believe that all rats make wonderful pets regardless of whether they are male or female. However, most people will develop a strong preference for one sex over the other, and this is perfectly normal.
We, humans, are individuals too and we all look for different traits and attributes from the animals we choose to share our lives. So, whether you lean towards buck or does, your rats can be active, interesting, and affectionate companions.