The dominant gene responsible for white coats in American Shetland ponies and miniature horses has
been identified, and is likely lethal if inherited from both sire and dam.
Dr. Elizabeth Esdaile and a research team from the University of California Davis Veterinary Genetics
Laboratory screened 19 unregistered Shetland ponies from one ranch for a variety of white pattern
markers.
The researchers found inexplicable coat colors in 14 of the ponies, and began looking for other
dominant white variants. They found that all 14 were heterozygous for the W13 gene. Prior to this
discovery, W13 had only been found in two Quarter Horses-Peruvian Paso crosses and one Australian
miniature horse family.
All ponies with the W13 allele had all-white coats with pink skin phenotype, no matter which other
white spotting variants were present.
The scientists also tested hair samples of 25 miniature horses and five Shetland ponies, each of which
their owners called “white.” Two of the miniature horses were heterozygous for the W13 gene. There
were no homozygous ponies; researchers say that homozygosity is most likely lethal.
The scientists noted that the Shetland ponies that had the W13 allele were not registered, and none of
the registered Shetland ponies had the allele. The team suggested that the unregistered Shetlands may
have some Miniature Horse breeding in their past.
The researchers said these results highlight the presence of the W13 allele in both Shetland ponies and
the American Miniature Horse, and the importance of testing for the variant since inheriting two copies
of the gene is most likely lethal.
Read the study here.
Read more at HorseTalk.
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