Dwarfism in Miniatures is generally believed to be genetic. Research is still ongoing spearheaded by John Eberth at University of Kentucky. four mutations have been found in one gene (D1, D2, D3, D4), with D1 being lethal. Tests for these four are available from the University of Kentucky, Gluck Equine Research Center.
At this point it’s important to get as many Minis tested as possible, so that breeding can be planned to eliminate the potential for dwarfs. Eliminating the genes responsible for dwarfism will take many years, but proper planning and the KNOWLEDGE/EDUCATION about dwarfism is the first step.
There is a Facebook Group (Miniature Horse Dwarfism Test Results – spearheaded by Susan Corbett Oberg. Thank you Susan!!!) where breeders can share their testing results and a European database(Zwergenwuchs bei Equiden) has been established too.
It’s my personal opinion you should NEVER buy a dwarf intentionally as a pet (there are plenty of reputable people that will take them and give the an excellent care for as long as that may be) and breeders that knowningly breed dwarves and sell them as “Micro-Minis” or some other made up name are misleading the public and preying upon unsuspecting buyers. Dwarf Minis often have many health related issues that can be very expensive to manage. So if you’re undertaking the care of a dwarf for whatever reason, network with experienced care-givers (see resources below!)
Dwarfism Phenotypical Characteristics
Some Common Phenotypical Characteristics of Dwarfism in Miniature Horses
A Checklist for Miniature Horse Breeders (and Buyers)
____ Legs do not grow in length (normal bone growth does not occur and/or occurs unevenly at the epiphyses). Foals may appear “cute” at birth but as head size, body depth, length and width increase with age, the legs do not grow in length. This the adult dwarf appears to have an over-sized head and/or body for its overall height.
____ Dwarf Foals are often born with retracted tendons, club feet, buck knees, that cannot straighten at birth. Join enlargements and join deviations (epiphyseal growth irregularities) are common. Extreme cow hocks, extremely short gaskins, and severe sickly hocks all with varying degrees of visible ‘joint looseness’ and/or joint weakness are also common. Premature arthritic processess take place in most dwarfs, resulting in prorgessive ambulatory disabilities.
____ Undershot (Bulldog or monkey bite). The molars therefore are mal-aligned, requiring that teeth be floated much more frequently than for a normal Mini.
____ One type of dwarf has a large bulging forehead with extreme dish (convex) face and turned up nose. Overly large and protruding eyes (sometimes placed and uneven angles). Nostrils placed to high up on the face (brachycephalic). A second type of dwarf has a more normal shaped head and eye but the head is much to large for its body. This type of dwarf does not usually have an undershot jaw as described in #3.
____ Head obviously longer than the neck. The distance from the poll to the withers should always be at least 1.1 times the distance from the tip of the nose to the poll. (In full size horses, the neck is almost 1.5x longer than the head.) In some dwarfs, the neck is so short that the head appears to come directly from the shoulders.
____ Girth depth is greater than leg length; enlarged entrails and genitals. Pot bellies are inevitable.
____ Scoliosis, kyphosis andor lordosis (vertebral deviations) are common.
____ Often unable to rear or stand on hind legs. Odd tilting backwards gait, with shoulder markedly higher than croup.
____ Mental retardations and inactivity/depression (possibly due to pain) are often sequel to the various forms of dwarfism.
** I have this document in an MSWord form if you would like a copy email me. It was complied by Barb Naviaux and the AMHA Genetics Committee.