Greying*

Important: this test is only possible with 30 mane/tail hairs plucked out with the hair root (no EDTA blood!). A mutation in the gene STX17 causes the greying phenotype in horses. Horses with this mutation are born coloured but gradually lose their hair pigmentation (not skin pigmentation) until they are grey or white at an age of about 6- 8 years. The mode of inheritance is autosomal dominant. Heterozygous horses will be grey-white and, in most cases, never be completely white. Some horses show some speckling or a "flea bitten" pattern. Horses that are homozygous for the mutation will be completely white at an early age. Horses with the grey mutation show a high incidence of dermal melanomas (70- 80% of Grey horses older than 15 years have melanomas) and reduced longevity. Homozygous carriers of the grey gene as well as horses born with a black coat seam to have a higher risk to develop melanomas compared to horses born with a brown coat.