Chrome. It’s something we hear frequently mentioned in horse circles but not so much elsewhere—unless we’re talking about the Google Web browser, motorcycles, or maybe classic cars. Part of the horse industry’s lexicon for generations, “chrome” has unwittingly joined the general public’s word bank with Triple Crown hopeful California Chrome’s namesake—his distinctive white markings.

California Chrome gets a bath on May 22, 2014, at Belmont. 

Photo: Chelsea Durand/NYRA

My colleagues at our sister publication, The Blood-Horse/, have followed California Chrome closely on his journey to becoming a Triple Crown contender. We haven’t seen a Triple Crown winner since Affirmed captured it in 1978. Blood-Horse has reported on everything from his pedigree to his owners to his support team; these writers and editors have really compiled rich and compelling information about this big flashy chestnut  and the feat he’ll attempt to accomplish tomorrow. But as someone who focuses on the biology behind these animals, I’m going to describe part of this racehorse that probably has little to do with speed (unless you’re superstitious), but that I find fascinating: The “why” behind his chrome.

California Chrome is a chestnut with a blaze and four white socks—a coloring that captures attention and is favored in many corners of the horse industry. I asked two equine geneticists about California Chrome’s chrome, and color in racehorses—one with extensive experience in researching inheritance of color (Samantha Brooks, PhD) and the other at the helm of important genetic research on the skeletal system and joint disease (Jamie MacLeod, VMD, PhD).

I consider Brooks, formerly of the University of Kentucky and Cornell, and now an assistant professor of equine physiology at the University of Florida, the queen of horse color. She weighed in on what dictates a foal’s markings. “White skin lacks melanin pigment, either because the cells that make pigment have malfunctioned, or are absent,” she says.

So, what lies beneath California Chrome’s red coat is black skin, and his facial markings cover white (it looks pink).

Markings land where they do for a reason. “The cells arise from the region of the spinal cord during embryonic development and travel around the embryo, arriving at the feet and the forehead last,” says Brooks. “Thus, any process that slows this cell migration down results in white socks and blaze, be it a cow, horse, mouse, or dog (or even people!). Genes causing white on a foal usually impact this migration in some pattern, resulting in patches of skin that lack melanocytes.”

(Me-la-no-cytes. [\mə-ˈla-nə-ˌsīt] Practice saying this so you can use this information at tomorrow’s Belmont Party.)

Because the face and feet are the most distant from the spinal cord in the developing foal, Brooks explains, you’ll often see white in both places.

In other words, California Chrome’s melanocytes didn’t cover ground in the womb as quickly as he does now on the track.

[pullquote source="Dr. Samantha Brooks"]When it comes to the usual blaze/socks, we have not observed any health issues. There is the old adage that four white socks is bad luck, or indicates weak feet, but physiologically that has not been proven.[/pullquote]

You won’t see the same exact markings in family members, full siblings (and even cloned horses—though it’s important to note there’s no cloning in the Thoroughbred industry). Indeed, “the migration is a race,” she says. “Some days even a fast horse won’t make it all the way to the finish line. Just the same with these cells, while the genes are telling them where to go, they may hit a speed bump or two along the way and never end up in exactly the same spot every time. Now the trends in the amount of white are highly heritable (as seen in other breeds, such as Paint Horses, known for color), but the precise placement of the pattern is all due to chance.”

As far as health itself, nothing really separates Chrome and other horses wearing white from their less flashy cousins. Mice are another story—white markings can adversely impact fertility and hearing and, in more severe mutations leading to white spotting, blood cell production. ”When it comes to the usual blaze/socks we have not observed any health issues. There is the old adage that four white socks is bad luck, or indicates weak feet, but physiologically that has not been proven.”

MacLeod, who is the John and Elizabeth Knight chair and professor of veterinary science at the University of Kentucky’s Gluck Center, and also a racing enthusiast, says he recalls “horse folks claiming that white feet, which I think simply reflects nonpigmented germinal cells in the coronary band, results in a ‘softer’ foot,” but he couldn’t think of a cell biology reason why that would be the case. I referred to my trusty Adams and Stashak’s Lameness in Horses, Sixth Edition, and indeed, it says, “Contrary to popular belief, pigmented hooves are not stronger than nonpigmented hooves,” going on to note that there are neither differences in stress-train behavior of ultimate strength properties between pigmented and nonpigmented hooves, nor are there differences in the fracture toughness of hoof keratin.

Interestingly, horses’ white markings have much to do with our relationship with horses through history. “It is a well-known phenomenon that white markings often appear during domestication of a species,” Brooks notes. “This may occur because we protect white marked animals from being singled out by predators (meaning they would otherwise be gobbled up by predators but, instead, we’ve protected them and allowed their lineage to continue), but some folks think that this may be a result of these same migration genes on the patterning of neurons (and, thus, behavior of melanocytes and nothing to do with predators) during development. Tough to prove though.”

Brooks points out that certain coat color spotting patterns predate domestication, however. These may have served as camouflage.

MacLeod is generally immersed in the world of cartilage damage and repair from a genetic standpoint (part of it involves interesting experiments on salamanders that can regenerate tissue) but has kept up with his colleagues’ genetic studies worldwide involving white skin and photosensitization (sensitivity to ultraviolet light) and gray horses and melanoma. Most other studies surrounding pigmentation have their focus in breeds other than Thoroughbreds.

I asked MacLeod if he gravitated toward certain markings in his racing picks. “In handicapping, which I do occasionally for fun and at most $2 bets, I try to assess the physical athleticism of each horse entered in the race,” he replied. “I screen the horses in the paddock, select my favorite three, and then review past racing performance and workout details in the program to select my predicted winner.”

I love this part and kind of wish I was a scientist when I read it: “Coat color does not register as a relevant variable in this process,” he continues. “That said, my hunter/jumper background from decades ago will draw my eyes to horses with interesting and ‘flashy’ white markings.”

So what about Chrome’s chances tomorrow? From a geneticist who knows the equine musculoskeletal system inside and out at the cellular level: “My primary wish, as always, is that all of the horses and riders have a safe trip,” MacLeod says. “This is far and away the most important issue, but beyond this consideration, I will be among the many people pulling for California Chrome. The horse and his connections have a great story (on a number of levels) and I certainly would love to see a new Triple Crown winner. I do believe, however, that the Belmont is shaping up to be a challenging race. I hope that California Chrome is a clear winner of the Belmont on Saturday and earns the revered status of ‘Triple Crown winner’ both honestly and unambiguously.”

I’m with the scientist. May you run a safe, honest, and stunning race, Chrome, much faster than your melanocytes ever did.

California Chrome gets a hug from Willie Delgado on May 27 at Belmont as Alan Sherman looks on.

Photo: Raisher/NYRA