Respiratory Tract Abnormalities and Racehorse Performance

Abnormalities in the throats of yearling racehorses will negatively impact the horses' athletic potential, making careful evaluation of these structures an important part of the prepurchase examination.

"Veterinarians routinely evaluate the throats of potential racehorses via external visual assessment and an internal endoscopic evaluation. The larynx and pharynx are highly scrutinized as abnormalities are known to adversely affect airflow and therefore athletic performance," explained Katherine S. Garrett, DVM, from Rood and Riddle Equine Hospital in Lexington, Ky.

To better determine the association between the endoscopy results and racing performance, Garrett and colleagues retrospectively reviewed the medical records of 2,954 yearling Thoroughbreds examined between 1998 and 2001. Arytenoid function (AF) was assessed using a modified Havemeyer scale (grade I, II.1, II.2, III, or IV) and the epiglottic structure (ES) was assessed using a scale from 0 to IV. The also subjectively analyzed the length of the epiglottis. The yearlings' racing performance was obtained using an online database.

For both AF and ES, the higher the scores, the more abnormal the function or structure were.

Key findings of the study were:

  • Horses with grade II.2 AF had significantly less earnings as 4-year-olds compared with horses with less than grade II.2 (grades I and II.1)
  • Grade III AF was associated with fewer starts and less earnings in horses at both 3 and 4 years of age, and
  • An ES grade more than II (grades III-IV) and a short epiglottis were associated with fewer earnings at 3 and 4 years of age.

"These data suggest that yearlings with grade I or II.1 AF, or grade 0 to II ES, have a similar athletic potential to one another," concluded Garrett.

"The definition of "abnormality" is somewhat amorphous, since resting endoscopy is not necessarily an accurate predictor of what happens during exercise," she noted.

The study, "Endoscopic evaluation of arytenoid function and epiglottic structure in Thoroughbred yearlings and association with racing performance at two to four years of age: 2,954 cases (1998-2001)," was published in the March 15, 2010 edition of the Journal of the American Veterinary Medical Association. The abstract is available on PubMed.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.