At this point, the genetic basis of reduced-switch syndrome has not been definitively determined. It appears to be the result of a recessive allele (unlike rat-tail syndrome), and even homozygous animals may show variable degrees of expression. It does not appear to affect white hair, so white-haired animals may be homozygous for the allele and not show any signs of reduced switch or hair length (also true for the rat-tail syndrome). To date, reduced-switch syndrome has been observed mostly in herds in areas with cold winters, and so it may be expressed more strongly or simply be more obvious in areas with cold weather. In addition, limited pedigree analysis suggests that the trait appears in herds that trace back multiple times to a particular and popular Texas Longhorn bull that has been used widely for artificial insemination. (Or, possibly, to two such bulls that are themselves related). Therefore, the frequency of this trait appears to be related to inbreeding (and in particular, to linebreeding these popular bulls), although the trait may also appear in herds that have no significant inbreeding history.
