Upper Respiratory Tract Disorders Evaluated in Detail

What do you get when you "scope" 1,005 horses after 230 races, each within 24 minutes of the race, with the cooperation of 97 trainers over 28 race meets? A great deal of valuable data about the equine throat and the impact disorders of the throat can have on racing.

"Considering that upper respiratory tract abnormalities are widely thought to be a leading cause of poor performance in athletic horses, few reports exist describing the association between performance and respiratory tract disorders in natural populations of racehorses," relayed Montague Saulez, BVSc, MS, Dipl. ACVIM, PhD, MRCVS, head of the Section of Equine Medicine at the University of Pretoria, based in Onderstepoort, South Africa.

Grade 5 mucus accumulation

A tracheobronchoscopic image of a racehorse with Grade 5 mucus accumulation.

In an attempt to fill this void, Saulez and colleague Bruce Gummow, BVSc, MMedVet, PhD, Dipl. ECVPH, FACTM, MRCVS, performed endoscopic exams on the upper respiratory tracts of a large number of Thoroughbred racehorses after racing. They identified the prevalence of pharyngeal, laryngeal, and tracheal disorders in South African Thoroughbred racehorses and the impact of these disorders on athletic performance.

The investigators assessed horses for laryngeal function (LF, abduction of the arytenoid cartilages, presence/absence of left recurrent laryngeal hemiplegia, or "roaring"), pharyngeal lymphoid hyperplasia (PLH, nodules of lymphoid tissue, "pimples"), amount of tracheal mucus, and other disorders such as defects of the epiglottis. They assigned a grade to LF, PLH, and tracheal mucus (low grade refers to minimal changes, whereas a high grade, a 4 or 5, represented major changes/deviations from normal).

"Overall, we found a low prevalence of Grade 2, 3, and 4 LF, epiglottic entrapment, subepiglottic cysts, and epiglottic deformities," reported Saulez.

He and his colleagues identified a higher prevalence of the following:

  • Grade 2, 3, and 4 PLH (found in 63% of examined horses);
  • Laryngeal debris (43.5%);
  • Tracheal debris (21.9%); and
  • Tracheal mucus (99.5%).

Findings Saulez considered interesting were that Grades 2 and 3 PLH were associated with impaired performance (i.e., fewer wins) and that Grade 4 LF abnormalities did not negatively affect performance.

"The impaired performance seen in horses with Grade 2 and 3 PLH was most likely due to fewer starts," commented Saulez. "Grade 4 LF did not appear to reduce performance, which was certainly surprising as affected horses are reported to have more severe hypoxemia than unaffected horses."

Saulez and Gummow cautioned readers that upper respiratory tract conditions are multifactorial in nature and advise, "One should be cautious when attempting to infer causality to a particular disorder. This study demonstrates the varied prevalence of disorders affecting the pharynx, larynx and trachea of racehorses competing in South Africa."

The study, "Prevalence of pharyngeal, laryngeal and tracheal disorders in thoroughbred racehorses, and effect on performance," was published in the October 10, 2009, edition of the journal Veterinary Record. The abstract is available on PubMed.

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