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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!"

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 populous.
This is in part due to their lack of availability to the general public
 relevant to the availability of standard-sized rats, 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 that 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.
This includes the NFRS who has set out a provisional standard for dwarfs which can be found HERE
They have a good turnout at shows and there are more and more breeders picking up and specialising in dwarfs. 

There are indeed some unscrupulous breeders claiming to keep and breed dwarf rats when they are, in fact, just runts. No solid pedigree can be produced for these rats, nor can their lineage be traced 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 genetically smaller. This is what makes them different from a runt or from a line that is selectively bred for size.

Some contention exists between keepers as to whether or not dwarf rats can be housed with standard-sized rats. 
While some breeders segregate dwarfs and standards, others do not. 
The truth is that dwarfs and standards can be housed together...however, this can increase the chances of injury to the dwarfs in the group should a fight break out.
With some people claiming that if a line is sound enough to be homed out as pets, they should be sound enough to be housed with any other rat, and others claiming that standard rats will maim and/or kill dwarfs 100% of the time, there is a cloud of confusion regarding the ethics of housing the two together.

Our advice would simply be to not house them together. This will eliminate any doubts and confusion for you as an owner.
If you cannot guarantee (and you can't) a smooth, no qualms introduction in your rolling group (and you should have a rolling group), then it is best to keep EITHER a dwarf group or a standard group. Unless you plan to have two separate groups for the two sizes.

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 Karni Mata Rattery in Germany.
After a few generations and lots of outcrossing into a more established 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 that better suited our goals.
As of December 2023, we no longer work with dwarfs. This is due to wanting to focus and establish our standard varieties.
We may seek to work with dwarfs again once we have the time to, but for now we are happy to recommend wonderful breeders up and down the country who continue to maintain and improve this wonderful variety.

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
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