Hair loss due to over-grooming (hair nibbling, whisker-eating) has been observed at The Jackson Laboratory for many years among mice in the C57BL/6J and related strains, i.e., C57BL/10J, C58/J, C57BR/cdJ, C57L/J and the congenic histocompatibility lines based on the genetic background of C57BL/10 and C57BL/6. These include the various B10.A lines, the B10.D2 lines, B10.LP lines, B10.129, B6.C, etc. The over-grooming behavior is seen in other strains, but the frequency is usually very low.
In every case where over-grooming occurs the hair will grow back again if the mice are separated into individually occupied cages. If only one whisker-eating mouse is present in a cage, it can be readily identified by its own full set of whiskers. If there is more than one whisker eater or if the hair loss is diffuse and involves areas other than the muzzle, the whisker eater cannot be as readily identified .
The occurrence of hair loss, the size and shape of the affected area, and the frequency of a particular pattern are variable. Mice of the C57BL substrains are much more prone to hair loss than other strains and certain congenic histocompatibility strains are especially susceptible.
At The Jackson Laboratory the type of alopecia resulting from social interaction of the mice – over-grooming - is considered a normal characteristic of C57BL/6J and related mouse strains and no attempt is made to prevent distribution of such mice. In some instances mice with no evidence of hair loss at the time of shipping will arrive at the consignee's facility with alopecia on the body. In such cases the hair grows back after one or two weeks in the animal room environment.
Hair loss caused by over-grooming is not a problem in our colonies. We are aware of the situation, the cause in not clearly understood, and the method of prevention (other than isolating the mice) is not known.
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