ABOUT THE SILVER DAPPLE DILUTION GENE
Hand painted resin sculptures
pictured above created by Laura Behning
What do silver dapples look like, and how is the gene inherited?
Silver dapple, sometimes simply called "silver" (Rocky Mountain Horse breeders call it "chocolate"; in Australia, it is called "taffy"), is a dilution gene that only affects black pigment, with an added affinity for lightening the mane and tail to various shades of
silver gray through platinum. The name is a bit of a misnomer, as some silvers don't have dapples, other than those "good health" dapples other colors get as well.
Since the silver gene only has an effect on black-based horses, if a
black, bay, brown, buckskin, etc. horse has the silver gene, it will be a silver. The manes and tails on silvers can vary in shade from stark white through very dark (often they darken with age), but they often retain a "core" of darker hair in the center of the tail and darker "roots" in the mane, with lighter hairs at the tips of the mane. A red silver (light bay silver) has a light mane and tail and chocolate or charcoal colored lower legs instead of the black points of a bay, and can be mistaken for flaxen chestnut. Black or brown silvers, a color which is common in the Rocky Mountain horse, can also be mistaken for flaxen liver chestnuts. Since the silver gene is not visible on true chestnuts- because they have no black pigment to dilute- silver can seemingly "skip" generations through chestnut "carriers". It is theorized that these "stealth silvers", along with actual silvers being mistaken for "chestnuts", enabled the color to
be basically unrecognized in the Morgan breed until the present day.
The silver gene is
dominant, so one parent of a silver must be silver or a chestnut carrying silver. The genetic designation for silver is "Z".
How can I tell if my horse is a silver?
Modern technology at UC Davis offers a test for silver dapple and is recommended if anyone has questions about their own "suspect silver" Morgan. Remember, chestnuts can carry the gene but don't express it, so
even if your "suspect silver" is a chestnut, it could still be carrying the silver gene, particularly if its pedigree goes back to the Dan/Nellie Skinner horses through an unbroken line of "chestnuts". Breeding a silver or silver carrying chestnut to a black or bay, particularly a homozygous black or bay, should give you silver offspring 50% of the time.
IMPORTANT NOTE: Silver dapple is not the same thing as flaxen, although the light manes and tails of silver dapple horses may have a somewhat similar appearance. Flaxen is a separate gene that only
visually affects chestnut horses (but can be carried by black based horses). I've had many questions about horses such as Book's End Trademark, Mantic Peter Frost, WHF Whistlejacket, etc. but these are all dark chestnut flaxens and not silvers. Similarly, dark palominos can look very much like silver dapples, but they are the result of the cream gene on a chestnut base in combination with a heavy sooty overlay, not the silver dapple gene.
The silver dapple test will sort these out if there are any doubts. Looking at the pedigree of a horse can give clues to help tell the difference in really difficult cases where
testing has not been performed. To see just how easily colors can be confused for something they look like but are genetically different from, visit
"Not Silver" page, as well as the Morgan Colors
Where does the silver dapple color come from in the Morgan breed?
The currently confirmed silver lines in our breed all trace back to the 1916 registered-as-chestnut stallion named Dan
(Headlight Morgan X Kate B), and were produced when he was crossed on the dark bay mare Nellie Skinner (Kansas Ranger X Lady Skinner, by Headlight Morgan) and her
daughters Dan's Baby (by Dan) and Betty Skinner (also by Dan). While there are most certainly mistakes made in color registration
(even today with our better knowledge of color genetics!),
most unrecognized silvers are registered as chestnuts, not as bays. For this reason it is less likely that Nellie Skinner, rather than Dan, was the
source of the silver gene.
Dan sired just seven registered offspring and they are all listed in the register as having a light or flaxen
mane and tail. Cavey, Dan's Bess, Dan's Betty, Betty Skinner and Dan's Baby are the five registered-as-chestnut mares by Dan that have presently confirmed (or suspected)
silver descendants. There were two other Dan offspring: Patcheco, who did not breed on, and Brady, who did. In his pictures Patcheco appears to be a silver; Brady may have been as well.
It is possible that the color is coming from Dan's sire Headlight Morgan himself. Headlight produced 169 offspring, although a
significant proportion of them did not breed on to the present day, which might explain the seeming lack of other silver descendants from him.
Headlight was chestnut (confirmed from photographs), so could have been carrying the gene. And indeed,
there could be other silvers from these lines out there, as yet unrecognized.
Dan's dam Kate B is registered as a bay,
so again, if she was the color source, it should have been visible on her.
Unconfirmed "suspect silver" descendants of Dan
Another possible silver line in our breed may be through the horses descending from the 1957 registered-as-chestnut stallion Honor (Triumph's Leader X Hondorine, by Silgal's Improver- sire of silver source mare, Broadwall Golden Girl). Honor has many "chestnut" color lines to Dan on BOTH sides of his pedigree. As an example, when the registered-as-chestnut Honor was bred to the registered-as-chestnut mare RB Sioux (Senator Allen X RB Sophie), the BAY gelding Oak Acre Starfire resulted. One of Starfire's parents must have been a silver. It is possible it was not Honor, but instead RB Sioux; her dam, RB Sophie (who was out of Cavey, by Dan) was also registered as chestnut. When RB Sophie was bred to the chestnut stallions Senator Allen and Loren Belle, she produced the BLACK RB Mary and the BROWN RB Colonel, respectively. RB Sioux has bred on through her chestnut daughter Stillwater Coalita by Dakota Joe (Honor X Mission Bell, out of Betty Dean). Honor had 82 offspring, 51 of
which were registered chestnut and 17 palomino. Many of them had the Oak Acres prefix.
Who are the currently known silver dapple Morgans?
At this time, there are less than 100 silver Morgans in the breed. They are
listed on the home page of this site.
SILVER DAPPLE TESTING
On October 9, 2006, a multi-university study on the silver
dilution in the equine was published - and Morgans played a starring role in it!
Early in 2006, Morgan breeders Laura Behning of Brookridge Morgans in Covington, GA and
Tamara Dirrim of Tamar's Ventures in Hamilton, IN were contacted by Sofia Mikko
of Uppsala University in Sweden about a study she and several other scientists
were doing on the silver dapple gene. Sofia wanted to check their results across
various breeds that had the silver dilution. Tam and Laura provided hair samples
from their silver dapple Morgans. Both the silver dapple colt Unconventional owned
at that time by Laura and the chestnut
(carrying silver) mare Amanda's Suzie Q owned by Tam are also pictured at the end of the
study, which can be downloaded
here (PDF format).
The silver dapple study has
resulted in a test for the gene, which
is now being offered by testing facilities such as UC Davis.
AN IMPORTANT NOTE ABOUT ASD AND THE SILVER DAPPLE GENE
ASD is Anterior Segment Dysgenesis, a malformation in the anterior segment of the horse's eye.
A 1999 MSU study theorized that ASD sometimes "piggybacks" along when the gene for silver is inherited. In its heterozygous form, ASD is of no consequence to the horse (this is the "cysts only" form, or Aa); it is not progressive, and does not affect vision. Homozygous ASD horses may have their vision affected (this is generally termed "ASD affected", or AA). Horses can be examined by a certified equine opthamologist to determine if the problem exists. Unfortunately, ASD is not always detected on an eye exam.
Most of the early research on ASD was done in Rocky Mountain horses, a breed
which is predominately silver (they call it "chocolate"). Responsible breeders simply do not breed silvers to other silvers to avoid getting homozygous silvers- which may be ASD
affected. It is hoped that a test for ASD will eventually be available. For more information, we recommend reading:
Michigan State University's ASD webpage
The 2006 Swedish University study on the silver gene seemed to indicate that there
was some question as to the actual existence of the ASD
disorder outside of the Mountain Horse breeds, and that its link there is
more one of bloodline than color. A more recent study (2009) found eye
abnormalities in the Icelandic Horse population, indicating that the link
between silver and ASD, now called MCOA (for Multiple Equine Congenital Abnormalities)
is most likely found across all breeds. The most up to date information on MCOA
and silver can be found here:
Equine Multiple Congenital Ocular Anomalies maps to a 4.9 megabase interval on horse chromosome 6
Multiple congenital ocular anomalies in Icelandic horses (2009)
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I would like to
thank the following people who have helped me in my research on silver
Morgans over the years and/or for their assistance with procuring photos
for this website: Kristal Homoki, Nancy Harris, Carroll Whiting, Janie and Claire
Murphy, Susan Graf, Linnea Sidi, Don Britton, Jack and Ginny Muse, Bobbie Zeulner, Joyce Urroz,
Shery Jesperson, Bobbie Zeulner, Nancy Caisse, Suzanne Edmonds, Nancy Castle, Sherry Siebenaler, Lisa Holec, Susan Motter, Melanie Pewe, Linda Erber, Lesli Kathman, Joanne Curtis, Margaret Gardiner, Sharon Harper,
Tamara Dirrim, Wendell Williams, Janine Welsh, and Susan L. Ewart.
Without all these wonderful folks offering information and photos for this project, it would not have
become a reality. Check back here often for updates and new photos which will be added as they become available!
Back to the Silver Dapple Morgans Project home page.