Veterinary session

The merle colour in dogs (Merle: blackbird) is caused by a retrotransposon insertion in the SILV gene, thus resulting malfunction in the eumelanin producing pigment cells. In homozygous (MM) individuals congenital auditory and ophthalmologic disorders are common, therefore the mating of two heterozygous (Mm) dogs should be avoided, also at the breeds having this trait - like the Mudi for example - it is forbidden. Some of the colours however are fully characterised by pheomelanin pigment (e. g. cream, beige, fawn), which are not affected by the merle gene, making it impossible to recognize the heterozygous individuals based on their phenotype (hidden merle). Traditionally the certain identification of hidden merle dogs can only be made based on them having merle offspring, but test mating cannot be considered as a reliable method.

Our aim was to test a fast, reliable and cost-efficient genetic method in the Mudi breed because in this breed white and fawn colours can also be found besides the merle colour - thus increasing the chance for hidden merle individuals.

In our study we used 25 hair and/or buccal swab samples collected from Hungarian and foreign dogs, then multiplied the exon 11 of the SILV gene with polymerase chain reaction (PCR) method from the purified DNA. Agarose gel electroforesis was used to detect the PCR products (M and m alleles) and separate them by size. We compared our genotype results with the dogs' phenotypic traits (colour of the eyes and the fur).

According to practical observations blue eye is solely caused by the merle gene in the Mudi breed, this observation was confirmed by our DNA test, so in these simple cases hidden merle dogs can be detected by their phenotype. Eye colour however is not always affected by the merle gene, so the genetic test is the only reliable way to identify hidden merle individuals, which is important to prevent puppies with decreased viability.