Who would have thought that baldness could be found in mammals other than middle-aged men, let alone the laboratory mouse? Unlike in Natalie Portman in “V for Vendetta,” baldness is never a good look for mice. For the most part, the cause of baldness (alopecia) in the laboratory mouse is a mystery.
If mice are group housed, barbering (over-grooming, fur nibbling and whisker-eating) may contribute to the alopecia. Barbering is a characteristic social interaction among C57BL/6 and C57BL-related mice (C57BL/10, C57BR, C57L, C58, and C57BL congenic strains). It is an expression of dominance. The dominant mice physically nibble or pluck fur and whiskers from their cage mates. In some instances mice with no evidence of fur loss at the time of shipping arrive at a customer’s facility with alopecia.
The only way to prevent barbering mice is to isolate the responsible mice or the ones being barbered. Afterwards, the fur usually grows back. If there is only one fur-/whisker-eating mouse in a cage, it can be readily identified by its own full set of fur/whiskers.
If there are several whisker-eaters in a cage, or if the fur loss is diffuse and involves areas other than the muzzle, the whisker-eater may not be as readily identified.
The amount of fur loss, the shape and size of an affected area and the frequency of a particular pattern are highly variable.
Stress might also induce alopecia. So might genetic and environmental factors, such as season, humidity, caging type and diet. However, among C57BL/6 and related strains, no infectious agents, immunologically mediated reactions or mutations are known to cause alopecia.
In our C57BL/6 colonies, the overall incidence of alopecia is low, but we have noticed several trends:
Fur loss is significantly more prevalent among females than males
Severe fur loss is greater in mice housed in pressurized, individually ventilated (PIV) racks than in conventional cages
Fur loss is more frequent during the winter than the summer
Diet or dietary fat may affect the incidence of alopecia (after we began feeding our mice with 6% fat instead of 11% fat chow in April 1997, the incidence and severity of alopecia in our C57BL/6J colonies decreased considerably)
Like people, mice aren’t perfect. Although C57BL/6J and related mouse strains are, for whatever reason, more prone to develop alopecia than other strains, they have many redeeming qualities. Being the most commonly used inbred mouse strain, they are extremely well characterized. A wealth of baseline phenotypic data is available for them in the Mouse Phenome Database. This degree of characterization can save you lots of time and money and reduce the overall number of mice you use. Many mutations and transgenes have been generated in or backcrossed to the C57BL/6J strain, providing a plethora of C57BL/6J mouse models for studying human disease. And, C57BL/6J was the first mouse strain to have its genome fully sequenced.
Now, are you ready to perform some experiments with C57BL/6J?
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