"When we looked at total earnings, we found buyers were paying far too much for poor quality horses," Hill says. The better predictor for earnings, she adds, was how the horses ranked on Equinome's report card, which assigns horses to a performance class based on how its genome compares with those of elite horses in her database, with class 1 being the best and 4 the worst. Her message: Not even the experts can distinguish a 1 from a 4 if they don't know the genes. "When we did the statistics, we found class is a more accurate predictor of total earnings than yearling sale price," Hill says. "Buyers were paying just as much for class 4 as for class 1. This is a bit of a fright, really."
The classic case of all this horse sense gone wrong is the story of The Green Monkey, a handsome bay colt with top-notch bloodlines that went to auction in 2006. The colt further impressed shoppers with a fast breeze—a breeze is a test run two-year-olds make before auction. Bidding began at $2 million that day in Florida. In little more than eight minutes, the horse sold for $16 million, the highest price ever paid for a thoroughbred in public auction.
It ran only four times and never won a race.
Genes and maps
When it comes to published academic research, Hill may be champion among the geneticists engaged in the search for the secrets of equine athletic potential.
In addition to publishing the discovery of the "speed gene"—actually a gene that controls the expression of the muscle growth factor, myostatin, in a January 2010 Public Library of Science paper—she has published research on several more genes and is seeking patents for some, including myostatin (MSTN).
Despite its nickname, the gene doesn't really play a role in how fast a horse runs, but rather how far it likes to run. Horses homozygous (having two copies) of one version (allele) of the gene—the so-called CC horses—are sprinters, she says. The CC means the horse has two copies of the DNA base cytosine at a particular place on the myostatin site. Those homozygous for the DNA base, thymine, at that site (the TT horses) are endurance performers. And those with one C and one T can show up on either side of the spectrum.
Among the other genes she says play a role in thoroughbred performance are peroxisome proliferator-activated receptor-γ coactivator-1 alpha (PGC-1α), which is involved in skeletal muscle adaptation to exercise; pyruvate dehydrogenase kinase, isozyme 4 (PDK4), involved in glucose regulation, expression of which increased almost fourfold after sprints; and cytochrome c oxidase subunit 4 isoform 2 (COX 4I2), involved in respiration. Hill showed a single-nucleotide polymorphism—placed in the genome where a single nucleotide is altered—in this gene is "strongly associated" with elite sprint racing performance.
Hill's assessment of thoroughbred performance is heavily dependent on what myostatin allele it starts with, and she has often looks for performance genes in the light of a horse's myostatin status. For instance, a study in her lab suggested that PDK4, which contributes to glucose regulation, may play a role in thoroughbred performance. When a follow-up study failed to replicate the finding, she decided to look again, but this time she sorted the horses according to their myostatin allele. Her finding: PDK4 alleles affected the performance of only those horses with the long-distance TT myostatin allele.
The approach is unique to her lab. In terms of uncovering specific genes and publishing on them, she nearly has the field to herself. Few other thoroughbred geneticists have expressed interest in identifying individual genes.