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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:

  1. it is not a serious health threat
  2. it is not very widespread within the population
  3. it is most prevalent in horses with chocolate/flaxen colouring
  4. 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."