Last year a study was released which detailed newly discovered information about Equine Dwarfism. This study by Dr. Eberth revolutionized what we thought we knew about Equine Dwarfism. Click here to read the paper. Dr. Eberth discovered that there are at least 4 different mutations of Equine Dwarfism. Labelled D1, D2, D3 and D4. These 4 mutations have been found within the population of Miniature Horses. Dwarf Miniature Horses and Friesian horses have tested negative for these 4 mutations therefore more mutations are expected to be discovered. The amount of mutations that may be discovered is unknown at this date and time.
Horses who are heterozygous for any one Dwarfism mutation have a normal phenotype. Horses who are homozygous for any Dwarfism exhibit varying degrees of Dwarfism traits, however, D4 is homozygous lethal. Horses can have combinations of different mutations; i.e. D2/D3 or D3/D4, etc. D1 is lethal when combined with other Dwarfism Mutations.
Tawny Horse stresses the importance of DNA testing and encourages all Miniature Horse owners to DNA test their Minis for all 4 of these mutations.
Information about the Equine Dwarfism testing can be found at the Gluck Equine Research Center website.