Also, Knight's whites are not sun sensitive, another albino trait. "We live in the desert, so they can't be," she quipped. "But I've found their skin is very cool to the touch. Because they're white, they reflect heat and they have very rapid body-heat loss."
Researchers at the University of California, Davis, have been studying horse-color genes for more than 20 years. Dr. Ann T. Bowling, who died in January 2001, was the forerunner in coat-color genetics, mapping out the possible combinations that could create different patterns and hues. Her work continues at UCD's School of Veterinary Medicine and Veterinary Genetics Laboratory.
Seven basic genes determine horse color. All non-white horses carry a recessive white gene. Only rarely does that white gene become dominant and express itself in an all-white horse. That dominant white gene prevents the unborn foal from forming pigment in its hair and skin. This differs from the gray gene, where the foal is born with pigment but gradually loses its color with age, much like the silvering of a person's hair. All gray Thoroughbreds have at least one gray parent, a fact that's often used in determining lineage.
Roaning can happen in any color horse, but these foals have a mixture of white and pigmented hairs from birth in a distinctive pattern. Roans develop more white hairs with age. The Jockey Club has registered grays and roans in the same category since 1994.
A dilution gene can fade a horse's basic genetic color coding into something totally different. When this gene takes over, bay becomes buckskin and chestnut fades to palomino. If a foal receives a dominant dilution gene from both parents, its coat can turn out a very pale cream color. Typically, this comes from breeding two palominos or buckskins. These pale offspring are called cremellos or perlinos. Their eyes are often blue, another trait of the dilution gene.
Bowling's theory on white Thoroughbreds is that the combination of two dominant white genes--one from the father, one from the mother--would be lethal.
That hasn't been proven in Thoroughbreds because no all-white stallion has been bred to an all-white mare. "Classically, you figure these things out by breeding lots of animals," said Dr. Danika Bannasch, chief of the genetics service at UCD's Veterinary Medical Teaching Hospital. "But it's not so obvious in horses. You don't have a big litter of puppies to compare."
In Paint horses, there is a lethal white gene carried by overo Paints. Foals affected by this gene die soon after birth due to intestinal tract defects.
Most of the mysteries the genetics lab tackles regard inherited diseases and defects such as this deadly gene, which occurs in several different horse breeds, including Thoroughbreds. The UCD lab offers testing for the lethal white overo gene.
Airdrie Apache, who is cross-registered as an overo Paint, has been tested and does not carry this lethal gene, said Knight.
Bannasch is currently helping the American Quarter Horse Association decide how to register an all-white foal born of two non-white parents.
Besides the presence of a dominant white gene, a white horse could result from the crossing of two patterned horses. But this, too, is mostly theory. "It's confusing--and exciting," added Bannasch. "But it will take longer in horses to determine what's really going on."
Knight, 57, has always had a passion for horses that looked different. The daughter of a fisherman, she grew up on the rugged Oregon coast in the cheese country of Tillamook.
"I got my first horse at age nine, first stallion at 14, and first registered Quarter Horse at 21," she recalled. "It's been a long, slow ladder to climb." Knight started buying and selling horses while still in grade school. "I started with ponies and never quit," she said.
In 1971, Knight moved to central Oregon and got into the horse trailer business, often driving a semi-truck packed with new equipment from Oklahoma to Oregon. "I was pretty fearless," she recalled. On the side, she continued breeding Quarter Horses, with a particular passion for unusual red duns and buckskins. She bought her "little piece of sage brush" near Redmond with the intention of starting a mare and foal operation in her retirement.
Eventually, Knight sold her trailer business and moved to Washington, where she met Irvine. In 1994, the couple retired back to Oregon, to what they dubbed Painted Desert Farm with the goal of raising colorful sport horses. They built a 1,800-square-foot log cabin plus facilities for the horses on the 50-acre ranch.
"This is our hobby," she said of the farm, "and things kind of snowballed." Her interest turned to Thoroughbreds after she lucked into the black stallion Prince Stanley, a grandson of Secretariat with almost all-white legs and white splashes on his tummy. She had advertised in The Blood-Horse for a true black stallion with excessive white markings, and Prince Stanley fit the description like a Paint portrait. One of his foals, Resistance Free, became the inspiration for a Breyer model horse.
"He's magnificent," Knight said of Prince Stanley. "He's sired quite a few of these beautiful Thoroughbreds." Painted Desert acquired Airdrie Apache soon after Prince Stanley, and Knight started dabbling with more colorful combinations. Besides his white foals, the stallion produced Painted La Riva, a filly who is getting second looks at Portland Meadows. Trained by Jim Keene, Painted La Riva is a bright red chestnut with a blond mane and tail, white socks over her knees, white stomach, and markings that "look like little white angels dancing on her neck," said Knight. "She's absolutely spectacular."
Now that Knight's focus has turned to combining speed and beauty, she and Irvine have been shopping the Kentucky sales for mares who have a lot of white as well as quality in their genes. The couple routinely looks for such sires as Marquetry, Northern Dancer, and Vice Regent, all known for bold markings in their progeny. Their broodmares include daughters of Storm Cat, Vice Regent, Relaunch, Secretariat, Riva Ridge, and Icecapade, plus a full sister to the Devil's Bag stallion Devil His Due.
And Knight intends to keep experimenting with her splashy mix of pure Thoroughbred Paints. "With few exceptions, there's no place to buy a spectacularly colored Thoroughbred," she added. "If you've got one, keep it."