|The ASD (anterior segment dysgensis) eye problem is an ophthalmic abnormality
caused by a dominant gene found in some Rocky Mountain Horses as
well as Mountain Pleasure Horses and Kentucky Mountain Saddle Horses. ASD
is NOT a degenerative eye disease, it is an inherited (genetic) defect
in the formation and development of the eye, early in embryonic development.
Of all the horses with ASD almost all of them have acceptable vision which
will not worsen with time.
One of the most popular colors among the mountain horses, the chocolate with white or flaxen mane and tail is related to the "silver dapple gene". Dr. David Ramsey's (DVM) research at Michigan State University, has shown a pattern that indicates the ASD condition is probably
linked to the color combination of chocolate with white or flaxen mane and tail. Exactly where this link occurs, of how it occurs, is currently not known for sure. It is best to treat the "suspicious" cases as if they were carriers until a genetic test is available
Research underway hopes to develop a genetic (DNA) test that will diagnos ASD horses (AA), horses with cysts (Aa) and normal horses (aa) in a simple and inexpensive test. Until a genetic test is developed, phenotype (physical appearances) of the horse, and skilled, thorough eye examinations are the only means to identify ASD horses.
The horses with ASD (anterior segment dysgensis) have problems in the anterior (front) part of the eye which did not develop normally. In some cases abnormalities found in the anterior part of the eye, also have abnormal development in the posterior (back) part of the eye. This genetic (inherited) condition (ASD) is identified in the studies by the symbol "AA" . Horses with less severe involvement, but who have eye cysts and are carriers of the condition are labeled "Aa". "Normal" eyes are identified as small "aa".
The "aa" horse exhibit no sign of eye abnormality. However, they
could be carriers of the genetic
Horses heterozygous for the trait (Aa) have cysts of the ciliary body
and peripheral retina, and
Some ASD "AA" horses will suffer no visual impairment at all; some will be born blind or go blind later in life. Of the horses examined by Dr. Ramsey, approximately 14% were ASD A veterinary ophthalmologist needs to check all breeding stock, to determine the animals status PRIOR to breeding.
The current findings are supported by a "grant" to Dr. Ramsey, he has established a research fund at Michigan State University to support RMH research. That grant money is now depleted and monies must come from other sources. All donations will be used to develop a genetic test to identify the genetic status of RMHs. All donations are fully tax-deductible. You can make a tax deductible donation to:
The University will send you a letter of receipt of your donation for your tax records. Also note: the research is under the auspices of Michigan State University and is independent of RMHA control.
The Rocky Mountain Horse Association (RMHA) have published stringent guidelines for breeding. Moreover, they have given all ASD information available to the entire membership.
This abnormality is not restricted to the Rocky Mountain Horse. David T. Ramsey, DVM, has examined found registered as either Kentucky Saddle Horses (KSH) or registered as Mountain Pleasure Horses (MPH) with eye abnormalities the same as those of Rocky Mountain Horses. Analysis of pedigrees from affected horses revealed similar lineage and ancestry compared with the RMH.
Board of Directors of the Kentucky Mountain Saddle Horse Association
met with Dr. Gus Cothran at the University of Kentucky Animal Pathology
Lab to establish their guidlines for determining the extent to which the
ASD condition affects the Kentucky Mountain Saddle Horse. The board believes
that there is a much higher percentage of normal horses within their breed
because the KMSHA accepts horses from many genetic lines and the
books remain open for mares to be registered with the association. It has
taken the Kentucky Mountain Saddle Horse Association longer in achieving
separate breed status because they continue to accept horses into the registry
from other breeding lines, and cannot become a breed until they close the
books. However they feel the Kentucky Mountain Saddle Horse and will
be less susceptible to other genetic problems caused from breeding too
closely within specific horses lines.