Low/High Risk Rats

Norway Rats: White Markings, Coats and Colors

Unfortunately, Metal Monkey Exotics no longer keeps or breeds Norway rats!

This is a simple list of what different markings are high or low risk for megacolon or other rampant health problems associated with the common history (i.e. pet store propagation) or the actual known health concerns associated with the genes creating the phenotype of the animal. (i.e. homozygous lethal)

The biggest concern with white markings would be megacolon or megacecum.

Megacolon – the inability to pass feces, eventually backing up the colon, distending the belly and ultimately causing death. It is a painful experience that is always fatal, and can’t be accurately predicted without extensive research. (ratbehavior.org)

Since this disease cannot be easily predicted without extensive knowledge and records from each line of rats being bred, it is fair to say that avoiding high risk white-spotted rats will ultimately lower the risk for megacolon.

It is also worth mentioning that the circumstances necessary for megacolon will not always manifest in white marked rats, or that rats without these white markings are 100% safe.

For help in identifying the patterns and colors, I have a simple gallery, and also see the AFRMA.org  website.

The following listings are considered “safe” markings, either by themselves or combined in any way. This is not an exhaustive list, this is guideline to low risk rats.

Low Risk


  • -Self (or solid color),
  • -Berkshires (belly is white)
  • -Irish (small heart, spot or line of white on chest)
  • -Hooded or bareback (color on head, neck and shoulders with a stripe running down the back, barebacks have no stripe down the back)
  • -Notched cap (color on head with small indent on the back)


  • -Straight
  • -Wavy
  • -Rex
  • -Harly


  • -Black
  • -Brown
  • -Cream/ Beige/ Champagne
  • -Albino
  • -Fawn/ Amber
  • -Siamese
  • -Russian blue
  • -Agouti (wild type)/ Cinnamon
  • -Mink


  • -Dumbo
  • -Top

High Risk


  • -Baldies/essex (white spots on head,often looks like a bald spot)
  • -Blazes or badger (white from tip of nose, meets as a point between ears)
  • -Odd-eyed rats, often with blazes (one red eye, one black eye, sometimes the red eye looks black unless light shined into)
  • -Lightning marks on face or split caps (split cap looks like a capped rat, but there is a line going through the middle of the head, down the nose)
  • -Black eyed white rats
  • -Banded/husky/roan rats (looks like a high sided berkshire, a long band of color down back of animal)
  • -High white rats (rats with irregular patches of color, can be combined with any before stated markings, )
  • -Down under (belly is marked with banding of color, much like a hooded rat; homozygous lethal)


  • -English blues from pets store: often weak immune systems, prone to hemorrhaging and die young. (Buy from established breeder)
  • -Merle and pearl: Pearl is homozygous lethal and will often accompany merle.


  • -Hairless, shorn or fuzzy: Very high maintenance due to lack of hair, most commonly; need for a high fat diet, frequent eye infections, scratches easily,  skin sores /infections, need to be kept warmer than other rats. Females will not produce milk, or very little.
  • -Tailless: Possibly unethical because animal cannot dissipate heat normally (rats use tail to control body temperature), or have same control and balance as tailed rats.

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