The first thing to mention is a miniature horse is not a dwarf horse.  
Dwarfism in our miniature horses is not something we like to publicise or talk about, but that does not make it go away. We have all gone to the circus and seen the “world’s smallest horse” and even had them paraded before us on television programs. Any breed of animal that attempts to reduce size has to accept dwarfism as an unwanted by-product.
We as breeders of miniature horses can do everything possible in our breeding program to minimise the possibility, ACAN testing is a way to minimise the risk. 


Some Common Phenotypical Characteristics of Dwarfism in Miniature Horse
A Checklist for Miniature Horse Breeders
  1. Legs do not grow in length (normal bone growth does not occur and/or occurs unevenly at the epiphyses). Foal may appear “cute” at birth but as body depth, length, and width and head size all increase with age, the legs do not grow in length. Thus, the adult dwarf appears to have an oversized head and body for its overall height.
  2. Dwarf foals are often born with retracted tendons, club feet and buck knees that cannot be straightened out at birth. Joint enlargements and joint deviations (epiphyseal growth irregularities) are common. Extreme cow hocks, extremely short gaskins and severe sickle hocks, all with varying degrees of visible “joint looseness” and/or joint weakness are also very common. Premature arthritic processes take place in most dwarfs, resulting in progressive ambulatory disabilities.
  3. Undershot jaw (“bulldog” or “monkey” bite). The molars, therefore, are also malaligned, requiring that the teeth require dentistry much more frequently than for a normal mouthed horse.
  4. 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 at uneven angles). Nostrils placed too high up on face (brachycephalic). A second type of dwarf has a more normally shaped head and eye, but the head is still much too large for its body. This type of dwarf does not usually have an undershot jaw.​
  5. Head obviously longer than 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 1.5 times longer than the head). In some dwarfs, the neck is so short that the head appears to come directly out of the shoulders.
  6. Girth depth deeper than leg length; enlarged entrails and genitals. Potbellies are inevitable.
  7. Scoliosis, kyphosis and/or lordosis (vertebral deviations) are common.
  8. Often unable to rear or stand on hind legs. Odd “tilting backward” gait, with shoulder markedly higher than croup.
  9. Mental retardation and inactivity/depression (probably due to pain) are often sequelae to the various forms of dwarfism.