Success
Story - Boo Surprised Everyone
Springtime is
an exciting season for Laurie Dunham who breeds horses at her ranch
Rock Ridge Paint Horses in Palm City, Florida. When her overo mare
was ready to foal, she anxiously awaited the moment, hoping to see
the classic splashy color of her Paints. Her hopes were shattered,
however, when the foal came out all white. She had already witnessed
the fate of one lethal white filly in her breeding program and it
was with a heavy heart that she called her veterinarian to come out
and euthanize this newborn white colt.
When lethal whites
occur, their intestines are not properly formed and they usually show
signs of colic and die within 12 hours after birth. "I had another
lethal white and she became real sick very fast," Ms. Dunham explained.
"I didn't want the colt to go through any suffering."
To her surprise,
as she waited for the veterinarian to arrive, the colt kept getting
stronger and stronger, began to nurse and even passed the first stool.
"Boo," as Ms. Dunham had dubbed the white colt, "was so strong by
the time the vet arrived that we just couldn't put him down," she
said. They decided to seek the advice of experts and called the UC
Davis Veterinary Genetics Laboratory. They were told that although
most lethal whites show signs of the disease within 12 hours, it sometimes
can take up to 48 hours for the signs to develop. They decided to
wait and see how Boo did. "Two days later," Ms. Dunham said, "he was
a healthy, bouncing baby and he's been going strong ever since. When
we spoke to people about this colt, they said he must have some color
somewhere. I have searched high and low, and there are no color specks,
just pink skin." Boo also has the characteristic blue eyes of lethal
whites.
To set the record
straight, Ms. Dunham decided to test Boo's genetics to see if he was
a living lethal white or if he was a carrier of the lethal white gene.
Blood and hair samples were obtained from Boo, his sire, his dam and
his paternal grand dam. The DNA testing revealed that, even though
Boo has the outward appearance (phenotype) of a lethal white, his
genetic test matched that of his sire and he does not carry the lethal
white overo gene. Boo's sire, Heathens Shooter, is an overo but he
does not carry the lethal white overo gene. Boo's dam, Peppers Promise,
is an overo who does carry the lethal white overo gene. Boo's paternal
grand dam, Whiskey Topsy, is a bay overo who also carries the lethal
white overo gene.
Now that Ms. Dunham
knows the carrier status of these horses, she is able use this information
in her breeding program. By crossing a non-carrier (solid) to a carrier
(overo), the offspring will be 50 precent overo (lethal white carriers)
and 50 percent solid (non-carriers), but no lethal whites will occur.
When crossing two overos that each carry the lethal white gene, 25
percent of the foals will be lethal white, 50 percent will be overo
(lethal white carriers) and 25 percent will be solid. Not all overos,
however, carry the gene and in some cases, tobianos and toveros (other
spotted patterns) can also be carriers of the lethal white gene, so
coat color alone doesn't provide the best information for avoiding
lethal whites.
"I am very interested
in using genetic testing in our breeding program and Dr. Bannasch
has been so helpful," Ms. Dunham said. "The overo color pattern is
the most desirable in the Paint industry but it is also the most difficult
to get. We are limited by the number of foals we can get out of each
mare's lifetime. You may as well deduct 50 percent of the foals for
no color. If we could get a better idea of what color pattern to cross
to get a higher color production, the financial reward would be considerable.
Genetic testing could help tremendously."
Considering the
economics of the Paint breeding industry, a $50 genetic test to identify
horses that carry the lethal white gene makes good business sense.
Why take the chance of producing a lethal white when there are alternatives
for producing the desirable overos? "Ms. Dunham explained, "The average
price for the great overo mares today is $100,000. You buy one of
those, figure you will start breeding her after her show career at
age five or six, you have approximately 14 potential years for foals.
Deduct seven of those years for no color and a couple for possible
barren years, that doesn't leave many foals to try to get your money
back out of the mare and to earn a living. As I own a few of these
mares, I am very interested in what Dr. Bannasch is doing in genetics."
Boo was broke
to ride last year and then was sold to Ms. Dunham's friend Kathy Cochran
in Ocala, Florida. He is still a stallion and has bred a few mares:
two solid and one Paint. So far, all his foals have had Paint coloring.
Even though Boo's skin is pink, he appears to do well out in the sun
and lives outdoors. Only the skin around his eyes is susceptible to
sunburn and requires preventive care.
It turns out that
Boo is also deaf, another genetic trait that appears to be linked
to the overo spotting pattern. Deafness in Paints is relatively rare:
only one percent ends up deaf and it seems to occur with a random
probability. Dr. Gary Magdesian of UC Davis is currently conducting
research on the heredity of this deafness in Paints. It appears to
be similar to the deafness that occurs in Dalmatians, Australian shepherds
and some cats. As for Boo, his deafness doesn't seem to cause him
any problems.
Boo, who is now
registered as "Heza Lethal Weapon," is a rare living all white Paint
who does not carry the lethal white gene. He would have been euthanized
if his owners had not decided to wait for the disease symptoms to
occur. For white foals of questionable parentage, UC Davis now recommends
waiting for symptoms of the lethal white disease to begin before deciding
to euthanize. Genetic testing is available at the UC Davis Veterinary
Genetics Laboratory to determine if a horse is a carrier of the lethal
white gene. In theory, if carriers are never bred to each other, the
lethal white disease could be eliminated from the horse population.
The Horse Report
is Copyrighted © 2001-2002 by the Regents of the University of California.
Use of this material for re-publication is allowed only by permission
of the Center for Equine Health.
Boo's
paternal grand dam, Whiskey Topsy, is an overo that carries
the lethal white gene (left).