Other scholars dispute this claim, pointing out that the Dartmoor Pony, while closely comparable in size to miniatures, lacks
any history of dwarfism problems. Regardless of the cause, it is all too certain that the American Miniature Horse has developed
as a breed that currently contains a significant amount of dwarfism in its genetics.
Bond Tiny Tim was a 19-inch-tall miniature registered by the AMHA, and though he reportedly suffered from a number of dwarfism-related
health issues, he was bred extensively allowing those defects to be passed on to thousands of descendants. Since 1989, however,
the AMHA has refused registration to any miniature showing two or more dwarfism characteristics in an attempt to reduce the
influence of these potentially damaging genes in the population.
There are more than 200 variations of dwarfism characteristics that have been cataloged and described in humans alone. Many
of these have been proven to be genetic. Such proof is currently lacking in horses, but the wide variation of dwarfism characteristics
is also seen in horses. Achondroplastic dwarfs unusually have short legs that often exhibit varus or valgus deformities. Deformities
of the face and jaw are common with an undershot jaw most frequently seen. Brachycephalic dwarfs have large bulging foreheads
and excess concavity or "dish" to the face. These minis have long heads and short, thick necks. All types of dwarfs can have
abnormalities to the hooves and teeth as well. An AMHA-approved grant in 1991 to the veterinary genetics laboratory at the
University of California-Davis was the first such full-scale attempt to investigate and determine the cause of dwarfism in
miniatures. This research looked at the effect of dystrophic dwarfism on various collagen genes, insulin-like growth factor,
growth hormone, and growth hormone-releasing factor and receptor. Important progress was made, but this area of research needs
more time and much more funding before the intricacies of dwarfism in the horse are fully explained.
Veterinarians often first encounter dwarfism problems during delivery as the domed forehead and enlarged skull of brachycephalic
dwarfs often causes problems as the fetus passes through the birth canal. Abnormalities of the legs and tendon contracture
can cause positioning problems that will also result in dystocias. Time spent advising owners about good breeding choices
will be well rewarded if fewer foaling problems are encountered and fewer genetic abnormalities are produced.
Overall, miniature horses require a level of care and management that often exceeds that of full-size horses, and yet, they
are most commonly owned by clients that have not yet developed a sufficient level of equine husbandry skill. Veterinarians
are in a unique position to offer advice and veterinary care to these often very motivated clients. Dental care and maintenance
should be done on a regular basis, often twice each year. Dietary consultation is important and can help to avoid many potential
medical conditions. Reproduction in the miniature horse can be a large source of potential problems, but it also can be a
new source of practice income if done properly. Ultrasound can be used effectively in miniatures and can lead to fewer problems,
more healthy foals on the ground and more satisfied clients. Ultimately, interest and expertise in miniature horse care can
be a practice builder for equine veterinarians and that, in itself, is no small thing.
Dr. Marcella, a 1983 graduate of Cornell University's veterinary college, was a professor of comparative medicine at the University
of Virginia. His interests include muscle problems in sport horses, rehabilitation and other performance issues.