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All About Dwarf Rats.

Excerpt: ‘Dwarf Rats’ by Debbi J. Neeham, 2005
"The spontaneous dwarf rat (SDR) was found in a laboratory colony of Sprague Dawley rats in 1977. It is a recessive mutation that causes them to have reduced GH or Growth Hormone which causes them to be up 40-75% smaller than their normal-sized counterparts, and in fact, a little larger than some fancy English mice. Dwarf rats have been found to be resistant to some cancers, as scientists have studied the effect of chemically induced cancer on dwarf rats and found dwarfs do not develop cancerous tumours like typically sized rats due to their lack of Growth Hormone. That is great news for those who keep rats in the rat fancy!"

About Dwarf Rats

Dwarfs are regarded as “forever babies” in the rat world.
They’re still the domestic Norway rat (rattus norvegicus domestica). They live with their standard friends and siblings in mixed litters, even being born to standard parents (should those parents carry the gene). 
So what makes them so different?

In short (no pun intended), dwarf rats grow to the size of a standard 6 week old kit (usually by 10 weeks), then as if by magic, they stop. Truly making them babies forever.
Almost ethereal in their features, they should exhibit large eyes, perfectly rounded ears, and a miniature frame.

They have a number of perks compared to standard sized rats, including:

  • A decreased risk of tumours. Almost never developing them thus living longer on average.

  • ⅓ of the size means ⅓ of the clean up. We have found them cleaner overall than standard sized rats.

  • They are just as sociable with humans and other rats, meaning they can be housed with standards (and other dwarfs, of course), and handled as much as standards.


While just a theory among a few breeders, we have found they tend to suffer less often with hormonal aggression (HA), possibly due to the lack of growth hormone.
However there is, currently, no study to back this and is based on anecdotal evidence from a few different ratteries. Ourselves included.


The dwarf gene is a simple recessive gene, meaning that it can be carried.
Dwarf kits can be the result of pairing:

  • Two standard rats that carry the dwarf gene (25% chance of each kit being a visual dwarf)

  • A standard sized “dwarf carrier” and a dwarf rat (50% chance of each kit being a visual dwarf)

  • Two dwarf rats (100% visual dwarf litter)

Kits are the same size when they are born, regardless of if they are dwarf or standard. It can take between 3 to 6 weeks to identify dwarfs in a mixed litter.

Dwarf rats are exactly the same in behaviour, diet, and general needs. They’re still fossorial, and require a good amount of floor space over climbing space (though they are very adept climbers).
Dwarfs are able to be introduced and housed with standard size rats. Though this is a controversial opinion to some, there are no issues that have arisen in our own standards when introduced to dwarfs. Either for breeding purposes or when being introduced into one of our large same sex groups.

Issues only tend to arise in hormonally or generally aggressive standard sized rats, wherein intros (regardless of if the new rats are dwarfs or standards) are a stressor and trigger otherwise hidden aggression.

Dwarfs Rats in the UK

While dwarf rats have existed since 1977 and are well known, even generally quite popular elsewhere in the world, they are yet to become as known among the British populus.
This is in part due to their lack of availability to the general public, and any information given about rats by large chain shops, British based YouTube channels, or websites dedicated to pet owning and sales, doesn’t include information about dwarfs. 

They also aren’t bred (purposely or by accident) by mills who supply pet shops. Thankfully.

There is some scepticism among British pet owners, particularly on Facebook, about whether or not dwarfs truly exist. Some go as far as to label those who claim to breed dwarf rats as scammers. However, dwarfs are recognised by several major rat clubs worldwide. Either as a provisional standard or a recognised standard.
It is true that there are some unscrupulous breeders claiming to keep and breed dwarf rats when they are, in fact, just runts. These rats do not have a solid pedigree, nor can they trace their lineage back to the first imports into Europe.
These rats will never breed true and will never produce dwarfs. They are, by all accounts, a scam.

True dwarfs are the result of two copies of the dwarf gene (drdr).
One copy = standard sized rat that carries the dwarf gene (DRdr).
They are not linebred to be smaller, they simply ARE smaller. This is what makes them different from a runt or from a line that is selectively bred for size.

Our Dwarfs

Our work with dwarfs started when we welcomed two dwarf bucks, a dwarf doe, and a dwarf carrier doe into the rattery from a well known breeder in Germany.
After a few generations and lots of outcrossing into our more established Agouti line, we started to see an improvement in temperament.

Ultimately, we stopped working with the descendants of this line due to importing alternative foundations for a new line focusing on black eyed c-locus. This has now become our main line due to lining up with our interests more.

We now specialise in:

  • Black Eyed Seal Point Siamese

  • Black Eyed Black Marten

  • Wedge Blazed Berkshire (Badger)

We currently only work with standard coats in our dwarfs. We frequently produce a mixture of dumbo and top eared.

Our old line focused more on velveteen in PED and RED based mink. This line can now be found in Denmark at Igloo Rats 🇩🇰

Opal Berkshire Dumbo Dwarf
Interested in dwarf rats?
Check out our rehoming information for more details!
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