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Baby Rat Development

This is merely a guide for those interested in how their baby has grown or for those curious about a babies development. I do NOT encourage breeding in any way without alot of research & preperation beforehand. It is not something to get into lightly!

The rat's gestation period is 19 to 23 days. 21 days is average.
Baby rats are called Kittens or sometimes the cute name Rittens (combing the name Rat + Kitten), sometimes they are also called pups.
Average litter size is between 8-12 babies though they can much have more! I have heard of litters up to 28! Dwarfs often have smaller litters of 3-5

This guide is based on an average time frame but each baby is unique and may develop at different rates. Some faster, some slower.


Pinkies (what newborn kittens are called) are born pink, naked and with eyes and ears closed.


Healthy babies will be very wiggly and may make loud squeaking sounds. They should have a very obvious milk band. A milk band is a white line underneath the skin in the stomach area, this lets you know that the babies have been eating well.

Around days 2-4

The kittens begin to develop their pigment. You may be able to judge their markings.

Sexing Pinkies

You can sex pinkies from birth even!

Looking at their genital region, the male's genitals will be farther apart from the anus then the female. It is usually pretty easy to tell if you have both a male and a female to compare them to.

Boy on the left. Girl on the right.

Black VS Red Eyed Pinkies

You can tell eye color right away!

Day 6

These were chunky babies, which is what you want to strive for!

Day 7

Finally a week old!

The babies are now beginning to grow fuzz.

Day 7

These are Siamese babies so they are still light colored

Day 10

Everyone is getting more fuzzier each day.

Day 10

Markings are showing much stronger

Day 11

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Day 13

Starting to look like little rats

Day 13

Little Teeth!

Between 1-2 weeks old

If you had trouble sexing babies before it has now become quite easy.

Only female rats have nipples and between 1-2 weeks old they will be easy to see.

Just be careful as they begin to get fluffier the nipples will become much harder to find, even impossible! So later on if you can't find nipples it doesn't mean it for sure is a boy. But if you do see nipples it is always a girl!

Don't mistake the belly button for a nipple :)

2 weeks old

Around 2 weeks the babies eyes should open.

This is when everything gets fun! Right away the babies will be much more active and mobile.

Still 2 weeks

At around 2 weeks the babies may begin to nibble on foods. They are still nursing for the majority of their food.

I also take the babies out for play time away from mom. I set up a playpen with a few different items & offer them foods to try.

Still at this age they don't stay away from mom for long.

Day 18

The babies are super fluff balls now! This is a great time for temperament testing.

Day 18 still

The babies are enjoying play time out of their cage alot more now. They love to explore new items and are already mastering climbing skills.

3 weeks old

At around 3 weeks the babies will begin to eat solid foods and may begin using the water bottle. They are still nursing but mom will naturally begin to wean them as this week unfolds.

They are starting to look like little rats now but still have fluffy baby coats.

Day 24

So much fluff!

Between 3-4 weeks old

Boys usually become easy to sex at this age. Their testicals are becoming quite noticable!

While only girls have nipples, since babies are so fluffy right now nipples can be nearly impossible to find. Never judge by lack of nipples alone.

4 weeks old

At around 4 weeks old the babies have usually stopped nursing and mom has weaned them. The babies now are eating solid foods on their own. Babies (less than 6 months old) need higher protein levels then adults. I prefer adults to have 14-16% protein and babies around 18% but less then 20%.


Breeders should not force the weaning, moms know what they are doing and wean the babies on their own.

Even though the babies no longer need mom to nurse, they are still just babies and need alot more from mom then just food. This is a key time in their development where they are learning rat social skills and what it means to be a rat! You should not separate babies from their mom this early!

5 weeks old

At 5 weeks I separate the boys from their mom and sisters. While most boys may not actually be mature enough to get the job done at this age, they are now old enough where it is possible for them to mate. Better safe then sorry, so make sure to always separate the boys at the 5 week old mark.


Even though the boys are now separated, they are still young babies. I feel they are still too young to go to their forever homes just yet...

6 weeks old

After 6 weeks old the babies are generally old enough to go off to their forever homes....

These two girls just turned 6 weeks and are about to be picked up by their new owner.

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Rats average lifespan is 2-3 years.

Rats reach fully grown between 6-8 months old.

They can be sexually mature at 5-6 weeks old. But it is very important for females to mature both physically and mentally before being mated, which is 5-6 months. Females do not go through menopause, fertility can wane but there is no specific age and rats over 2 years old have still been known to give birth. Older rats giving birth can come with many risks and complications.

Males may go through a hormonal period at around 6+ months old.


Rats can actually differ in size by quite a bit. Just like humans have different heights, weights and body shapes. You can have very large rats or quite petite.

In general female adult rats weigh between 300-450g and adult males weigh between 450-650g.

And adult dwarfs are around 80-115g some lines up to 120g. It is important to note that dwarf is a specific gene and not just smaller rats.

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