Some Eye Information About
Our Horses
In the past few years some concern has arisen
regarding "eye-problems" in the
Mountain Saddle horse. There are many
misconceptions and much misinformation being
passed about regarding these concerns, some of
which will be addressed below. However, in order
to put the minds of ourselves, our owners and our
breeders at rest, we have had the eye status of
the herd examined.
In 1998 all of our
broodstock was examined by a qualified
veterinary opthamologist (Dr. Melanie
Williams). Twenty-two animals, including our
stallions Tim's Choco and Northern Drifter,
had clear eyes. One mare (Choclate Flax) had
one cyst in one eye and one unregistered mare
had a detatched retina (likely due to an
unrelated injury). All 1995, 1996, 1997,
offspring had clear eyes. We will continue to
have all new broodstock and offspring
examined periodically to ensure that no
genetic eye defects are propegated through
our breeding program.
Just about every breed of horse has some
genetic abnormality; some inheritable problem.
The problem found in some Mountain Saddle horses
is an abnormality in the formation of the front
part of the eye (the anterior segment) and is
called Anterior Segment Dysgenesis (or ASD
for short.)
Dr. Ramsey, an ophthalmic researcher from
Michigan State Unversity, has been conducting
research into ASD and has been examining Mountain
Saddle horses for several years. An Eye Registry
has been established at MSU and has catalogued
data on all horses examined. His observations
about ASD can be summarized as follows:
- it is not a serious health threat
- it is not very widespread within the
population
- it is most prevalent in horses with
chocolate/flaxen colouring
- it can be corrected and all but
erradicated by responsible breeding
Below are some excerpts from two articles
published by Dr. Ramsey. These articles may be
read in their entirety at the RMH gentetics page.
"If you hear nothing else, hear
this: this problem is not that bad." And
please keep in mind that with careful
breeding we can breed this problem out or
very close to it within a few generations. In
the meantime, there is no reason that we
can't enjoy our wonderful horses. Enjoy that
puppy-dog temperament, calm demeanor, (and)
smooth gait..'
"The most common abnormal trait
that was documented was cysts that arise from
the ciliary body (inside the eye). These
cysts are never painful, do not limit vision,
and are therefore of no consequence to the
eye or the horse."
"ASD is not unique to the Rocky
Mountain Horse, it occurs in all breeds I
have examined that carry the Silver Dapple
gene.... This includes the Shetland Pony,
Miniature breeds, Rocky Mountain, Kentucky
Mountain Saddle, Mountain Pleasure, Morgan,
Bashkir-Curly, Naraganssett Pacer, and
Haflinger... The disease is probably just as
prevalent in some of the other aforementioned
breeds. It has only been studied extensively
in Rocky Mountain Horses because the breed
Association recognized it and was proactive
to determine whether the abnormality was a
severe defect."
"Over 2500 Rocky Mountain Horses
have been examined by veterinary
ophthalmologists in the United States and
Canada. Approximately 5% of Rocky Mountain
Horses that I have examined have two
"abnormal" copies of ASD. Only a
very small population of affected horses
(approximately 30 horses) have problems with
vision. All but two horses that I have
examined have had normal functional vision.
"The incidence of eye
abnormalities is highest in horses with a
chocolate coat color. Horses with a white
mane and tail color are at the greatest risk
of ASD... Selection of phenotypic
characteristics deemed most favorable
economically (coat and mane and tail color)
may have resulted in concentration of the
abnormal gene and subsequently a higher
incidence of eye abnormalities."
"Contrary to the published report
in Horse Illustrated, the Rocky Mountain
Horse eye is virtually unaffected. With the
exception of two blind horses from a
population of 2500 Rocky Mountain Horses
examined to date, vision is rarely affected
and the health of the eye is virtually normal
in Rocky Mountain Horses with ASD."
|
