There are two basic types of hairless rats, true hairless and ‘patchwork’ hairless.
True hairless rats have no fur at all on their bodies and usually no whiskers either. Sometimes they have fur as pups which falls out by the time they are 2-3 months old. There are many different genetic strains of true hairless, most if not all of which have come from laboratories, where they are used extensively for medical research. They are missing a part of their immune system called the thymus, which makes them susceptible to disease and allergies. Depending on which strain they are they can be prone to tumors, eye and respiratory infections, heart or kidney disease, diabetes or skin problems. The average lifespan of true hairless rats is 9-18 months old.
As it is impossible to tell what strain a true hairless rat is without genetic testing, it is important to obtain true hairless rats from reputable breeders who can provide a pedigree. Breeders are working on stronger stains of true hairless rats through out-crossing with healthy furred rats. Hairless females with few exceptions do not make good breeders. They generally do not lactate at all or enough to support a litter, and cannibalism or abandonment is common. To produce true hairless pups, breeders will mate a hairless male (homozygous) to a furred hairless carrier female (heterozygous for hairless). Half of the offspring produced should be hairless, the other half will be furred hairless carriers.
Patchwork hairless rats maintain a certain amount of short, soft fur on their bodies and patches where they are bald. The fur will periodically fall out and grow back in throughout the rat’s life in different patterns. They usually maintain whiskers though they are generally brittle and curly. While they are more prone to allergies, they are hardier than the true hairless rats and should live an average lifespan. The females also have no problems reproducing or raising litters. There are three strains of patchwork hairless rats:
1) Double rex: produced from two rex-coated parents (ReRe). Different from the other two strains as they tend to keep some fur on the face, head, feet and ankles while maintaining a mostly hairless body. If bred to a normal-coated rat they will produce rex-coated pups. If bred to a rex or velveteen-coated rat they will produce double rex pups.
2) Double Velveteen: produced from two velveteen-coated parents (CuCu). If bred with a normal-coated rat will produce velveteen-coated pups. If bred to a velveteen or rex-coated rat they will produce double velveteen pups.
3) Double velveteen/Double rex: produced from one double rex-coated parent and one double velveteen-coated parent (CuCuReRe). If bred to a normal-coated rat they will produce rex-coated and/or velveteen-coated pups.
Caring for a true or patchwork hairless rat is very similar to a furred rat. With less fur they need to maintain a higher body temperature which quickens their metabolism. They will eat and drink more than furred rats, and should be given some extra protein in their diets. A multi-vitamin formulated for rats can also be put into ther drinking water once a week. To help them stay warm a heating pad on LOW can be place under one third of their cage floor (make sure wires are out of range). Rats are social and should have a companion, but with true hairless rats I suggest keeping hairless with hairless as they will be more gentle with each other. Hairless rats can get scratched easily, and these should be tended to quickly with a safe topical cream. To further prevent scratches, use toys with no sharp edges, make sure hideaways have ample entry and exit space and that cages are coated wire, not just metal. Use a soft bedding instead of woodchips or corn cob which can irritate and itch. There are many on the market made from recycled newspaper, etc. Try to keep hairless rats away from other pets and put an air filter in the room to cut down on the chances of them developing allergies. It is very important to make sure the cage is clean and dry. Never keep your hairless rats by a window or in direct sunlight as they sun-burn easily.