preciousmetal.pdf

Misidentified and misunderstood,

the silver dilution gene has been

virtually unknown in the

Paint world until now.

By IRENE

STAMATELAKYS

ave you ever seen a silver horse?

Not a shiny gray, but a rare and

intriguing silver dilute? Chances

are, you never have. If you have,

chances are you didn’t know it.

Just ask Paint Horse owner Talia Chiodo,

who first learned about them while surfing

the Internet.

“I was just browsing equine Web sites when

I stumbled upon a photo of a silver dapple

horse,” recalled Chiodo. “I thought the color

was stunning. I decided to learn more about

it. So I Googled the term ‘silver dapple.’ ”

Chiodo found the Web site of Meadow

View Farm and Champs Guthrie AQHA, a

brown silver stallion, and came across a page

that had close-up photos of silver characteris-

tics—mottled legs, flaxen-tinted mane and

striped hooves.

“As I looked at the close-up of leg mottling,

a light bulb went off,” said Chiodo. “ ‘That’s

the same type of mottling Bella has!’ She also

has the flaxen mane and striped hooves.”

Living in Des Moines, Iowa, Chiodo owns

two Paint mares—Bella, whose registered

name is Wrangled From Heaven, and Bella’s

dam, Stars Angel Too.

“I had always doubted that Bella was a

dun,” said Chiodo. “As Bella aged, her coat

got darker and darker. She is now the darkest

shade of chocolate I’ve ever seen with no dun

characteristics whatsoever.”

With a chocolate-colored coat and other

silver characteristics, Chiodo wondered if her

Paint was possibly a silver. Did they even exist

in the breed?

“I immediately called APHA and asked

them if they had any silver Paint Horses on

file,” she said. “I was told that they did not.”

Not to be discouraged, Chiodo took the

next step.

“I knew it was a long-shot, but I decided to

test Bella anyway [for the silver dilution gene],”

continued Chiodo. “I got the results in about a

Right: Brown silvers are often mistaken for

liver chestnuts. Notice the lightened mane and

tail and dapples on Champs Guthrie AQHA,

who descends from Bow Champ, one of the

two known lines of silver Quarter Horses.

PAINT HORSE JOURNAL u FEBRUARY 2009 u 107

Above: Although

not confirmed by

genetic testing,

BN Pecos Pete

certainly looks like a

black silver. With his

light mocha coat,

dapples, and a

flaxen mane and tail

with dark roots, he

displays classic

silver characteristics.

The 2004 solid

gelding is by Black

Ty Affairs Kid and

out of Magnificant

Nina Blue.

Right: Some foals

with the silver

dilution gene have

white eyelashes,

which they later

outgrow. This is

a secondary

characteristic, not

absolute proof that

your foal is silver.

week. I was floored when I saw them. Accord-

ing to Bella’s results, she was a black silver.

“I was even more shocked after I tested

‘Angel’ [also registered as dun]. Her results

came back as buckskin silver. That means she

carries both the silver dilute gene and the cream

dilute gene—a rare combination indeed!”

Like many Paint owners, Chiodo was com-

pletely unfamiliar with the silver dilution gene

and the unique colors it produces by lighten-

ing the black pigment in the hair. While silver

colors are rare, they are growing in popularity

and certainly in the future we’ll find—or

breed—more silver Paints.

will affect black, bay, brown, buckskin, dun and

grullo horses, without changing sorrel, chest-

nut, palomino and red dun horses.While those

“red” horses don’t express the gene, they are

capable of passing it to their offspring, often

with surprising results.

There isn’t just one silver color but several

that vary with the horse’s base color. In the

past, these colors were called silver dapple,

silver chocolate and red silver, among other

terms. However, to simplify and clarify the

color names, today many breeders describe

horses using the base color plus silver.

Breeder Julia Lord of North Liberty, Indi-

ana, discovered Saddlebreds with the silver

dilution gene in 2002.

Silver characteristics

Before genetic testing for the silver dilution

gene was available, silvers were usually identi-

fied by their phenotype or external appear-

ance. Primary characteristics are diluted coat,

mane and tail colors. Secondary characteris-

tics include leg webbing, striped hooves, white

eyelashes on foals and sometimes dappling.

This dilution gene is unique because it mod-

ifies only the black pigment in the hair, leaving

the red pigment untouched. As a result, silver

108 u PAINT HORSE JOURNAL u FEBRUARY 2009

“Silver on a black base color is the shade

that comes to mind first when hearing the

term ‘silver dapple,’ ” explained Lord. “The

body color is diluted to a chocolate or mocha

brown shade, sometimes light enough to

appear similar to a sooty palomino.”

Black silvers are also mistaken for flaxen

liver chestnuts.

“[In bay silvers], the red pigment on the

body is unaffected, while the black on the legs

is slightly diluted and the black of the mane

and tail is more strongly diluted,” said Lord.

“The horse is not quite bay and not quite

chestnut either. Usually the legs are the main

clue that the horse is not chestnut—they will

be much darker than a chestnut.”

Brown silvers are often difficult to distin-

guish from blacks and bays, says Lord.

“The Agouti test [as the Agouti gene

controls distribution of black pigment] may

be needed to tell apart black-based from

brown-based silvers,” she explained.

Likebays,brownsilversareoftenmistakenfor

chestnuts. The silver gene can also dilute buck-

skins,dunsandgrullos.Thesecolorsarerareand

harder to identify visually, making them easily

misclassified.Maneandtailcolorsareimportant

clues that the silver dilution gene is at work.

“The gene tends to dilute the mane and tail

much more strongly than the body, often to a

silvery-white color, although this can vary and

may darken with age,” explained Lord.

Manes can range from platinum blond, to

flaxen, to slightly diluted. In some cases, the

mane is described as “self-colored” or the same

diluted color as the body.

Silver expert Lewella Tembreull of Pierz,

Minnesota, breeds Shetland Ponies, where the

color is quite common. She explains that in a

typical silver, “the mane changes in shade from

root to tip, with the core of the mane being

the darkest part. The lower tail is the darkest

part of the tail.”

The lower leg color is also affected, says Lord.

“They tend to have lighter hair on the lower

legs, lightest close to the hooves, and the lower

legs are often dappled, which is highly unusual

in other colors,” she explained.

While it is difficult to identify a silver coat

color in newborn foals, young horses do have

other distinguishing characteristics.

“Foals often have hooves with a very

strong and distinct striping pattern and

white eyelashes,” said Lord. “These traits are

helpful for identifying silver in foals but are

gradually outgrown.

“White markings themselves commonly

cause striped hooves.The hoof stripes that we

are talking about occur on legs with no white

markings.They seem almost universal among

silver Icelandics and Minis, but pretty rare on

silvers in other breeds.”

Also, since horses with a lot of head white

frequently have white eyelashes, it is impossi-

ble to classify a Paint as a silver gene carrier

based solely on this characteristic.

Some silver horses have pronounced

dappling, while others do not.

“The term ‘silver dapple’ can be misleading

because not all horses carrying the gene are

silver in color or have dapples,” said Monique

Matson, who owns Meadow View Farm in

Gaston, Oregon, with her husband, Ken.

Not all silvers display these secondary char-

acteristics, but they are helpful in identifying

carriers when the changes in coat, mane and

tail color are very subtle.

Genetics of silver

Experts say that the silver dilution gene was

possibly present in Icelandic horse populations

more than 1,000 years ago. However, the

exact cause of the silver coat color was discov-

ered only recently.

In October 2006, an international team led

by researchers at Uppsala University in Swe-

den, in association with BMC Genetics, pub-

lished its study, “A missense mutation in

PMEL 17 is associated with the silver coat

color in the horse.”

The study revealed that a mutation in the

gene PMEL 17 on horse chromosome 6

causes one amino acid to be substituted for

another and is responsible for a dilution of

the black pigment in the hair. The team

In your mind,

compare Andretti

MVF AQHA with an

ordinary bay and

you’ll see where the

silver dilution gene

comes into play by

diluting the black in

the body, mane, tail

and lower legs.

Note how the silver

gene has lightened

the mane, tail and

legs of this buckskin.

Stars Angel Too also

carries the sooty

gene which makes

her coat darker than

most buckskin

silvers.

confirmed that the silver allele (Z) is domi-

nant and, if present, will almost always pro-

duce the silver phenotype.

“Horses that are homozygous (ZZ) for

silver seem to exhibit a more diluted coat

color compared to the heterozygous (Zz)

horses, but this indication needs to be

verified,” wrote the researchers.

The exceptions are the red-based horses.

They do not show any effects of the silver mu-

tation and are hidden carriers, capable of pro-

ducing offspring with silver coat colors when

crossed with horses carrying the black gene.

Once the silver dilution gene was mapped,

a genetic test was developed and commercial-

ized, giving breeders a definitive tool to

distinguish silvers from other similar colors

and identify red-based carriers.

When silvers are misclassified as reds, they

usually go undetected until they produce a

bay, brown or black foal with a red mate.This

raises a flag with breed registries since two red

horses can only produce a red. Before the

silver test was available, the only other option

was to test for the red factor to show the

“chestnut” was genetically black.

“Very, very few people can tell certain shades

of chestnut from certain shades of silver bay

visually,” saidTrembreull. “I have years of expe-

rience telling the two apart, and there are indi-

viduals that I will not even attempt to classify as

silvervisually.Therearehorsesthattheonlyway

to determine if they are a silver bay or a chest-

nut is by red factor and silver testing.”

Geneticists continue to study the silver dilu-

tion gene because of eye abnormalities found in

Rocky Mountain Horses, Kentucky Saddle

Horses and Mountain Pleasure Horses. For

years, these problems have been attributed to

Anterior Segment Dysgenesis (ASD), a con-

genital,inheritedbutnotprogressivediseasethat

canaffecthorsesofanybreedorcolor.ASDwas

thought to be linked to the silver gene or color.

However, in a recent studies, the eye defects

found in Rocky Mountain and Kentucky Sad-

dle Horses were not those usually associated

with ASD. Also, researchers are not certain if

the problems are linked to a specific bloodline

or to the silver gene. Other breeds have not

found ASD in their silver horses. Further

research is necessary.

Searching for silver

Like any precious metal, silver is rare.

Where did the silver dilution gene come from?

Are there many silver Paints?

According to the Swedish-led study, silver

coat colors are relatively common in Icelandic

Horses, American Miniature Horses and

Rocky Mountain Horses.They have also been

found in the Morgan Horse, American

Saddlebred and Shetland Pony.

In the Morgan breed, “evidence suggests

Headlight Morgan as the possible source of

the gene,” said Lord.

Why is this 1893 “liver chestnut” stallion

significant?

“If he truly was carrying it, it may be much

more widespread than we think, as he sired

not only many Morgan foals, but was also

used as a sire of Quarter Horses on the

Burnett Ranch,” said Lord.

110 u PAINT HORSE JOURNAL u FEBRUARY 2009

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