A TINY CAUTIONARY TALE . . .
And What We Can Do About It
Whenever we select for small, we almost always select for dwarfism. It is seen for example in Dexter Cattle, Miniature Horses and other mini species. Dwarfism is a natural consequence of selecting for small size. The after affects of attempting to breed smaller – tiny – teeny can easily be seen by “Googling” equine dwarfism. Concerns that Miniature Horse breeders have is mirrored in their ongoing study of dwarfism. The following checklist was approved by the American Miniature Horse Association’s (AMHA) Board of Directors to assist breeders and inspectors in determining if, in fact, a given horse exhibits dwarf-like characteristics*. (The checklist appears with three columns for each listing . . . “None”, “Moderate” and “Severe”.)
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 enlargement 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 weaknesses are also 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 be floated 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 as described in #3.
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 greater than leg length; enlarged entrails and genitals. Pot bellies 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.
What to do?
Dr. Gus Cothran, Veterinary Integrative Biosciences Department, Texas A&M University, has agreed to process and archive blood samples from Miniature Donkeys free of charge in order to DNA test these animals for dwarfism markers. (Blood samples contain more of the DNA information available in blood needed by the lab than the usual hair samples required for parentage qualifications.)
All samples would, of course, be treated confidentially. The purpose of Dr. Cothran’s investigation would be to aim to identify the gene responsible for dwarfism in the Miniature Donkey so in the future a test would be able to indicate which individuals carry the dwarfism gene.
Dr. Cothran’s generous offer may help the Miniature Donkey Breed avoid future problems associated with dwarfism that other breeds have experienced. In all, 20 Miniature Donkeys bearing some if not all indicators of dwarfism** (as well as indicated in the above checklist) and 20 Miniature Donkeys who do not bear any indicators of dwarfism would be needed.
If you would like to participate:
. Determine beforehand which Miniature Donkey(s) you would like to have participate and photograph left and right sides of each to send along with their blood samples identifying each set of photos with corresponding blood samples – if not by name, by letter or number; i.e., A, B, C or 1, 2, 3.
. There is no definite deadline for submitting samples, so the next time your veterinarian makes a farm call ask him to draw two 10 ml tubes of blood from each Miniature Donkey submitted to save on an extra farm visit charge.
. When blood is drawn, chill these tubes in the refrigerator for several hours, wrap in newspaper and add a package (or two) of frozen peas. (Dr. Cothran’s iguanas will be happy!) Remember to send those photos . . .
. Ship your package by express mail (at least second day domestically) and the fastest delivery if mailing from overseas to:
Dr. Gus Cothran
Clinical Professor – VIBS
Texas A&M University
College Station, Texas 77843-4458
Dr. Cothran has been extremely generous in offering this opportunity to the Miniature Donkey community which will only help to benefit the future well being of our remarkable creatures. If you’ve any questions about this investigation please contact Ellen Dahlstet – firstname.lastname@example.org – 402-238-2738.
*Reprinted with the kind permission of the American Miniature Horse Association
**The NMDA Miniature Donkey Breed Standard defines dwarfism under Faults Not Acceptable In Breeding Animals as follows:
. A dwarfed animal has an overall stunted, thick-set appearance. They can have multiple deformities in the legs with large, coarse and knobby joints or cannons short and stumpy. They have disproportionate heavy heads, usually carried low.