Recent research indicates that endoscopic examination of yearlings can help determine their eventual racing success. However, researchers also showed certain abnormalities that in the past were considered indicators of poor performance were not predictive of actual athletic performance in the adult horse.
Veterinarians "scope" a horse's upper respiratory tract to look for any deformities of the soft palate or epiglottis, and to watch the movement of the arytenoid cartilages at rest. If not functioning properly, the laryngeal cartilages can't move out of the horse's airway, thus blocking air flow. These assessments have tremendous impact on sale recommendations and selling price.
Researchers collected information from the endoscopic exams of 427 Thoroughbred yearlings sold at the 1996 Keeneland September sale, and they followed the horses' racing careers over the next four years. Of the original group, 364 established race records.
The veterinarians involved in the study tried to determine if they were making the right pre-purchase recommendations based on a 30- to 60-second upper airway exam. "If you can't gain any prognostic information from endoscopic exams, then we shouldn't be doing them," said Dr. Jim Morehead of Equine Medical Associates in Lexington, Ky., one of the investigators in the study.
But the researchers discovered that these exams are, indeed, worthwhile.
As air moves through the larynx when the horse breathes, the arytenoid cartilages move. Some horses (coined "roarers," for the whistling sound they make) have nerve dysfunction in their larynx, preventing one of the arytenoid cartilages (usually on the left) from moving properly.
The movement of the arytenoid cartilages were graded from one to four, with conditions in each grade specifically defined: one is normal (both open maximally and concurrently); two indicates asymmetry (both open maximally, but not concurrently); three means the horse can't get the left arytenoid completely out of the airway (does not open maximally), and maintain it in the normal position; and four means the horse has one completely paralyzed arytenoid cartilage (which does not move).
Of the 427 examined, 149 were in grade one, 171 in two, 94 in three, and 13 in four.
Historically, it has been thought that horses with grade one or two would have superior performance on the racetrack in comparison to grade three and four horses. The researchers proved this theory true. Comparing purchase price with racetrack purses earned from ages two through four, the research showed yearlings found in grades one and two were more likely to recoup their purchase price than yearlings in grade three and four, by a difference of 34% to 20%.
"Our findings on arytenoid function are fairly consistent with what most already believed, and I thought it was nice that we put some hard numbers on our impressions because it gives you confidence to recommend things to clients that you've substantiated," said Dr. John Peloso, a partner in the Equine Medical Center of Ocala, Fla., and another participant in the study.
On the other hand, the research dispelled some beliefs on yearling upper airway conformation and racing performance. Veterinarians for years have thought that displacement of the soft palate, inflammation in the pharynx, and epiglottal function affected racing performance.
"Yearling throats are variable in their appearance as far as palate displacement, inflammation, and epiglottal function, and we found that those (scenarios) don't correlate with poor performance," explained a third member of the research team, Dr. John Stick, Professor and Chief of Staff at Michigan State University's Department of Large Animal Clinical Sciences. "If there's an obvious abnormality of the epiglottis or palatine (soft palate) function that's going to have a major mechanical effect on the horse, common sense prevails, because clearly there are some things that are so severe that the horse's athletic ability will be compromised. However, displacement of the palate or a juvenile-appearing throat should not necessarily be considered a problem when considering pre-purchase recommendations."
"This study should give us the confidence to perform a second examination in the horse that displaces their palate, or to give the horse the benefit of the doubt if we're on the fence," added Peloso.
The researchers hope their work will help solidify opinions at horse sales. "When people are looking at yearling Thoroughbreds, they need to be reserved in their comments on the palate and epiglottis, and rest assured that what they're seeing in the laryngeal grading will prove true and show in the horse's athletic career," said Stick.
Assisting Morehead, Peloso, and Stick in the research were Michigan State University investigators Dr. Frederik J. Derksen, chair of the Department of Large Animal Clinical Sciences, Dr. James Lloyd, and Dr. Pawin Padungtod, who worked to help extract the significance of the racing data collected. The study was published in the Oct. 1 issue of Journal of the American Veterinary Association