Recent research indicates that endoscopic examination of yearlings can help determine their eventual racing success. However, researchers also showed that certain abnormalities previously considered to be 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 (the laryngeal cartilages that if not functioning properly can’t move out of the horse’s airway, thus blocking air flow). These assessments have tremendous impact on sale recommendations and selling price.
Investigators in the study were Jim Morehead, DVM, of Equine Medical Associates in Lexington, Ky.; John Peloso, DVM, Dipl. ACVS, a partner in the Equine Medical Center of Ocala, Fla.; and John Stick, DVM, Dipl. ACVS, Professor and Chief of Staff at Michigan State University’s Department of Large Animal Clinical Sciences. Other MSU investigators were Frederik J. Derksen, DVM, PhD, Dipl. ACVIM, Chair of the Department of Large Animal Clinical Sciences; James Lloyd, DVM, PhD; and Pawin Padungtod, DVM.
The researchers collected information from the endoscopic exams of 427 Thoroughbred yearlings in 1996, 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 wondered 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 Morehead.
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 sound they make) have nerve dysfunction in their larynx, preventing one of the arytenoid cartilages (usually the left) from moving properly. The movement of the arytenoid cartilages is graded from one to four -- grade 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 doesn’t move).
Of the 427 examined, 149 were diagnosed as grade one, 171 grade two, 94 grade three, and 13 grade four.
Historically, it was thought that horses with grade one or two arytenoid function would have superior performance on the racetrack in comparison to grade three and four horses. Researchers proved this theory true by evaluating purchase price and racetrack purses earned from ages two through four. Thirty-four percent of the grade one and two yearlings recouped their purchase price, compared to only 20% of the grade three and four yearlings.
"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 Peloso.
On the other hand, the study dispelled some beliefs on yearling upper airway conformation and adult performance. Veterinarians have thought for years that displacement of the soft palate, inflammation in the pharynx, and poor 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 Stick. "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 his palate, or to give the horse the benefit of the doubt if we’re on the fence," added Peloso.
The researchers hope that their work will help solidify opinions at the 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.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.