A while back, I was doing some reading on equine color genetics when I came across information about the silver dapple gene.  I’m always interested in learning new things and when I started to read about this dilution gene, I immediately perked up.  The silver dilution gene acts on black points of the body and lightens them to varying degrees.  This can be expressed as either “black silvers” (white mane/tail, seal brown body, often dappled) or “bay silvers” (chocolate body, silver mane/tail that is darker at the roots, mottled silver legs).  I believe that Tiny may have the bay silver gene, which would explain her unusually light-colored legs and the silver in her mane. 

As I continued learning about the intricacies of equine coat color genetics, I discovered that the silver dapple gene is sometimes associated with ASD – Anterior Segment Dysgenesis.  ASD is an abnormal development of the eye and can result in impaired vision.  ASD is not restricted to horses with the silver dapple gene, but it is thought that there is a connection between the two conditions.  Horses are born with ASD – it is a congenital condition with varying degrees of severity.  There are several signs that a horse has ASD:  a ”pop-eyed” appearance, cysts, cataracts, or abnormal dilation of the pupil.  The retina is also occasionally affected.    So what should you do if you suspect your horse might be affected?  First, have him examined by an equine opthalmologist that has the necessary diagnostic equipment.  It is important to remember that ASD is not progressive and does not result in blindness, and that most affected horses continue to have normal vision throughout their lives. 

Further Reading:

A missense mutation in PMEL17 is associated with the Silver coat color in the horse.  2006.   Brunberg, et al.

http://www.horse-genetics.com/silver-dapple.html

http://www.silverequine.com/

http://old.cvm.msu.edu/research/mregl/asd.htm

Image courtesy of Scott Robinson

First off, I’d like to say a GREAT BIG  “THANKS!!!” to Mugwump Chronicles for reprinting my post on the history of the Appaloosa horse.  Welcome to all of Mugwump’s readers and thanks for all the comments that were posted regarding my article.  I had no idea that there were so many Appaloosa lovers on this scene – it’s nice to see my favorite breed well represented.  Please check out Mugwump Chronicles, if you haven’t already.  It’s a great source of training tips and information. 

One of the comments that was left on Mugwump’s site regarding my post was very intriguing.  Justaplainsam included a link to a site about a registered Quarter Horse stallion that has an Appaloosa blanket!  What?!?!?  It’s true – Reminic in Spots is a fully registered Quarter Horse stallion that has been parentage verified.  There is no question that this handsome fellow is all AQHA.  This discovery shocked and fascinated me.  I’d never heard of this happening before, so I started looking into it to see what might cause such an anomaly.  The information I found surprised me.

Reminic In Spots, Courtesy of YOR Appaloosa

When I started researching this topic I quickly came across the term “cropout.”  This term refers to a horse born to solid parents in a breed that typically does not exhibit excessive white or coat patterns, such as the Quarter Horse.  The cropout horse may have Appaloosa type coloring or Paint type coloring.  It is caused when one or both parents -although potentially solid colored – contributes a gene for color.  For those of us (like me!) that need a refresher on our genetics knowledge, an Appaloosa coat pattern will be expressed in offspring if the offspring has at least one dominant color gene from at least one parent.  Make sense?  In the case of Reminic, at least one of his parents must have had a color gene which was passed on to him.  Ba-da-bing – out pops a colored QH colt!  Surprise!  However shocking this may be, the information I discovered next was even more so.  Back in the day of the newly formed American Quarter Horse Association, these spotted foals occurred but could not be registered and were commonly sold as grade horses.  The Appaloosa Horse Club and American Paint Horse Association, which were also newly forming, began to allow these “undesireable” Quarter Horses to register with the breed association that they most closely represented.  As a result, some of the most highly influential Appaloosa sires in the history of the breed are actually spotted Quarter Horses born of two QH parents.  The list includes Colida, Joker B., Bright Eyes Brother, and Wapiti.  While these horses’ colorations were a surprise, and often a disappointment to their breeders, it is no mystery how they came to have color. 

Image courtesy of bankerssilvermoon, Flickr

Appaloosa spots are controlled by the Leopard complex, or Lp gene.  This gene produces different visual characteristics depending on the number and type of gene copies a horse has, ranging from striped hooves to full leopard spots.  The Leopard complex is complicated and well beyond the scope of this article, but further information can be found through The Appaloosa Project, a genetic study being undertaken to uncover the mysteries of the many Appaloosa coat patterns.  The important thing to remember is that not all horses with the Lp gene are loudly colored – sometimes they are solid with some mottling, sometimes they are a Varnish roan (easily confused with a true roan, which is allowable in the AQHA registry).  Varnish roans tend to continue roaning over time, often until they are nearly white.  It is entirely feasible that these subtly marked horses were registered as Quarter Horses as youngsters and went on to contribute their Lp gene to the gene pool, only to have it emerge generations later in a situation like Reminic’s.  In fact, many of these horses can be traced back to the breeding program of Coke Roberds, a Quarter Horse breeder who had a number of roan horses.  This article on Wapiti gives a thorough background on the breeding program of Coke Roberds.

Now that DNA testing and parentage verification are so readily available, horses like Reminic are able to register as fully papered Quarter Horses.  This discovery does inject a great deal of spark into the already hot topic of acceptable Appaloosa characteristics and registration.  It is also interesting to note that the ApHC has headed off any potential competition from colored QH stallions by disallowing breedings to any QH stallion exhibiting excessive white or undesireable QH traits (ApHC Handbook, Rule 204.B.2.a.1).  Hmmmmm…. kind of interesting, considering that those spots originated from some of our foundation stock years and years ago. 

Image courtesy of bankerssilvermoon, Flickr